sudoers(5) File Formats Manual sudoers(5)
NAME
sudoers - default sudo security policy plugin
DESCRIPTION
The sudoers policy plugin determines a user's sudo privileges. It is the
default sudo policy plugin. The policy is driven by the
/opt/local/etc/sudoers file or, optionally, in LDAP. The policy format
is described in detail in the SUDOERS FILE FORMAT section. For
information on storing sudoers policy information in LDAP, see
sudoers.ldap(5).
Configuring sudo.conf for sudoers
sudo consults the sudo.conf(5) file to determine which plugins to load.
If no sudo.conf(5) file is present, or if it contains no Plugin lines,
sudoers will be used for auditing, policy decisions and I/O logging. To
explicitly configure sudo.conf(5) to use the sudoers plugin, the
following configuration can be used.
Plugin sudoers_audit sudoers.so
Plugin sudoers_policy sudoers.so
Plugin sudoers_io sudoers.so
Starting with sudo 1.8.5, it is possible to specify optional arguments to
the sudoers plugin in the sudo.conf(5) file. Plugin arguments, if any,
should be listed after the path to the plugin (i.e., after sudoers.so).
The arguments are only effective for the plugin that opens (and parses)
the sudoers file.
For sudo version 1.9.1 and higher, this is the sudoers_audit plugin. For
older versions, it is the sudoers_policy plugin. Multiple arguments may
be specified, separated by white space. For example:
Plugin sudoers_audit sudoers.so sudoers_mode=0400 error_recovery=false
The following plugin arguments are supported:
error_recovery=bool
The error_recovery argument can be used to control whether sudoers
should attempt to recover from syntax errors in the sudoers file.
If set to true (the default), sudoers will try to recover from a
syntax error by discarding the portion of the line that contains
the error until the end of the line. A value of false will disable
error recovery. Prior to version 1.9.3, no error recovery was
performed.
ignore_perms=bool
The ignore_perms argument can be used to disable security checks
when loading the sudoers file. If enabled, the sudoers file will
be loaded regardless of the owner or file mode. This argument is
intended to be used for testing purposes and should not be enabled
on production systems.
ldap_conf=pathname
The ldap_conf argument can be used to override the default path to
the ldap.conf file.
ldap_secret=pathname
The ldap_secret argument can be used to override the default path
to the ldap.secret file.
sudoers_file=pathname
The sudoers_file argument can be used to override the default path
to the sudoers file.
sudoers_uid=user-ID
The sudoers_uid argument can be used to override the default owner
of the sudoers file. It should be specified as a numeric user-ID.
sudoers_gid=group-ID
The sudoers_gid argument can be used to override the default group
of the sudoers file. It must be specified as a numeric group-ID
(not a group name).
sudoers_mode=mode
The sudoers_mode argument can be used to override the default file
mode for the sudoers file. It should be specified as an octal
value.
For more information on configuring sudo.conf(5), refer to its manual.
User Authentication
The sudoers security policy requires that most users authenticate
themselves before they can use sudo. A password is not required if the
invoking user is root, if the target user is the same as the invoking
user, or if the policy has disabled authentication for the user or
command. Unlike su(1), when sudoers requires authentication, it
validates the invoking user's credentials, not the target user's (or
root's) credentials. This can be changed via the rootpw, targetpw and
runaspw flags, described later.
If a user who is not listed in the policy tries to run a command via
sudo, mail is sent to the proper authorities. The address used for such
mail is configurable via the mailto Defaults entry (described later) and
defaults to root.
No mail will be sent if an unauthorized user tries to run sudo with the
-l or -v option unless there is an authentication error and either the
mail_always or mail_badpass flags are enabled. This allows users to
determine for themselves whether or not they are allowed to use sudo. By
default, all attempts to run sudo (successful or not) are logged,
regardless of whether or not mail is sent.
If sudo is run by root and the SUDO_USER environment variable is set, the
sudoers policy will use this value to determine who the actual user is.
This can be used by a user to log commands through sudo even when a root
shell has been invoked. It also allows the -e option to remain useful
even when invoked via a sudo-run script or program. Note, however, that
the sudoers file lookup is still done for root, not the user specified by
SUDO_USER.
sudoers uses per-user time stamp files for credential caching. Once a
user has been authenticated, a record is written containing the user-ID
that was used to authenticate, the terminal session ID, the start time of
the session leader (or parent process) and a time stamp (using a
monotonic clock if one is available). The user may then use sudo without
a password for a short period of time (5 minutes unless overridden by the
timestamp_timeout option). By default, sudoers uses a separate record
for each terminal, which means that a user's login sessions are
authenticated separately. The timestamp_type option can be used to
select the type of time stamp record sudoers will use.
The tsdump utility, included with the sudo source distribution, can be
used to display the contents of a time stamp file. See
sudoers_timestamp(5) for details of the time stamp file format.
Logging
By default, sudoers logs both successful and unsuccessful attempts (as
well as errors). The log_allowed and log_denied flags can be used to
control this behavior. Messages can be logged to syslog(3), a log file,
or both. The default is to log to syslog(3) but this is configurable via
the syslog and logfile settings. See EVENT LOGGING for a description of
the log file format.
sudoers is also capable of running a command in a pseudo-terminal and
logging input and/or output. The standard input, standard output, and
standard error can be logged even when not associated with a terminal.
For more information about I/O logging, see the I/O LOGGING section.
Starting with version 1.9, the log_servers setting may be used to send
event and I/O log data to a remote server running sudo_logsrvd or another
service that implements the protocol described by sudo_logsrv.proto(5).
Command environment
Since environment variables can influence program behavior, sudoers
provides a means to restrict which variables from the user's environment
are inherited by the command to be run. There are two distinct ways
sudoers can deal with environment variables.
By default, the env_reset flag is enabled. This causes commands to be
executed with a new, minimal environment. On AIX (and Linux systems
without PAM), the environment is initialized with the contents of the
/etc/environment file. The HOME, MAIL, SHELL, LOGNAME and USER
environment variables are initialized based on the target user and the
SUDO_* variables are set based on the invoking user. Additional
variables, such as DISPLAY, PATH and TERM, are preserved from the
invoking user's environment if permitted by the env_check, or env_keep
options. A few environment variables are treated specially. If the PATH
and TERM variables are not preserved from the user's environment, they
will be set to default values. The LOGNAME and USER are handled as a
single entity. If one of them is preserved (or removed) from the user's
environment, the other will be as well. If LOGNAME and USER are to be
preserved but only one of them is present in the user's environment, the
other will be set to the same value. This avoids an inconsistent
environment where one of the variables describing the user name is set to
the invoking user and one is set to the target user. Environment
variables with a value beginning with `()' are removed unless both the
name and value parts are matched by env_keep or env_check, as they may be
interpreted as functions by the bash shell. Prior to version 1.8.11,
such variables were always removed.
If, however, the env_reset flag is disabled, any variables not explicitly
denied by the env_check and env_delete options are allowed and their
values are inherited from the invoking process. Prior to version 1.8.21,
environment variables with a value beginning with `()' were always
removed. Beginning with version 1.8.21, a pattern in env_delete is used
to match bash shell functions instead. Since it is not possible to block
all potentially dangerous environment variables, use of the default
env_reset behavior is encouraged.
Environment variables specified by env_check, env_delete, or env_keep may
include one or more `*' characters which will match zero or more
characters. No other wildcard characters are supported.
By default, environment variables are matched by name. However, if the
pattern includes an equal sign (`='), both the variables name and value
must match. For example, a bash shell function could be matched as
follows:
env_keep += "BASH_FUNC_my_func%%=()*"
Without the `=()*' suffix, this would not match, as bash shell functions
are not preserved by default.
The complete list of environment variables that are preserved or removed,
as modified by global Defaults parameters in sudoers, is displayed when
sudo is run by root with the -V option. The list of environment
variables to remove varies based on the operating system sudo is running
on.
Other settings may influence the command environment:
o sudoers options such as always_set_home, secure_path, set_logname,
set_home, and setenv.
o Command tags, such as SETENV and NOSETENV. Note that SETENV is
implied if the command matched is ALL.
o sudo options, such as -E and -i.
On systems that support PAM where the pam_env module is enabled for sudo,
variables in the PAM environment may be merged in to the environment. If
a variable in the PAM environment is already present in the user's
environment, the value will only be overridden if the variable was not
preserved by sudoers. When env_reset is enabled, variables preserved
from the invoking user's environment by the env_keep list take precedence
over those in the PAM environment. When env_reset is disabled, variables
present the invoking user's environment take precedence over those in the
PAM environment unless they match a pattern in the env_delete list.
The dynamic linker on most operating systems will remove variables that
can control dynamic linking from the environment of set-user-ID
executables, including sudo. Depending on the operating system this may
include _RLD*, DYLD_*, LD_*, LDR_*, LIBPATH, SHLIB_PATH, and others.
These type of variables are removed from the environment before sudo even
begins execution and, as such, it is not possible for sudo to preserve
them.
As a special case, if the -i option (initial login) is specified, sudoers
will initialize the environment regardless of the value of env_reset.
The DISPLAY, PATH and TERM variables remain unchanged; HOME, MAIL, SHELL,
USER, and LOGNAME are set based on the target user. On AIX (and Linux
systems without PAM), the contents of /etc/environment are also included.
All other environment variables are removed unless permitted by env_keep
or env_check, described above.
Finally, the restricted_env_file and env_file files are applied, if
present. The variables in restricted_env_file are applied first and are
subject to the same restrictions as the invoking user's environment, as
detailed above. The variables in env_file are applied last and are not
subject to these restrictions. In both cases, variables present in the
files will only be set to their specified values if they would not
conflict with an existing environment variable.
SUDOERS FILE FORMAT
The sudoers file is composed of two types of entries: aliases (basically
variables) and user specifications (which specify who may run what).
When multiple entries match for a user, they are applied in order. Where
there are multiple matches, the last match is used (which is not
necessarily the most specific match).
The sudoers file grammar will be described below in Extended Backus-Naur
Form (EBNF). Don't despair if you are unfamiliar with EBNF; it is fairly
simple, and the definitions below are annotated.
Resource limits
By default, sudoers uses the operating system's native method of setting
resource limits for the target user. On Linux systems, resource limits
are usually set by the pam_limits.so PAM module. On some BSD systems,
the /etc/login.conf file specifies resource limits for the user. On AIX
systems, resource limits are configured in the /etc/security/limits file.
If there is no system mechanism to set per-user resource limits, the
command will run with the same limits as the invoking user. The one
exception to this is the core dump file size, which is set by sudoers to
0 by default. Disabling core dumps by default makes it possible to avoid
potential security problems where the core file is treated as trusted
input.
Resource limits may also be set in the sudoers file itself, in which case
they override those set by the system. See the rlimit_as, rlimit_core,
rlimit_cpu, rlimit_data, rlimit_fsize, rlimit_locks, rlimit_memlock,
rlimit_nofile, rlimit_nproc, rlimit_rss, rlimit_stack options described
below. Resource limits in sudoers may be specified in one of the
following formats:
"value"
Both the soft and hard resource limits are set to the same value.
The special value "infinity" can be used to indicate that the
value is unlimited.
"soft,hard"
Two comma-separated values. The soft limit is set to the first
value and the hard limit is set to the second. Both values must
either be enclosed in a set of double quotes, or the comma must
be escaped with a backslash (`\'). The special value "infinity"
may be used in place of either value.
"default"
The default resource limit for the user will be used. This may
be a user-specific value (see above) or the value of the resource
limit when sudo was invoked for systems that don't support per-
user limits.
"user" The invoking user's resource limits will be preserved when
running the command.
For example, to restore the historic core dump file size behavior, a line
like the following may be used.
Defaults rlimit_core=default
Resource limits in sudoers are only supported by version 1.8.7 or higher.
Quick guide to EBNF
EBNF is a concise and exact way of describing the grammar of a language.
Each EBNF definition is made up of production rules. For example:
symbol ::= definition | alternate1 | alternate2 ...
Each production rule references others and thus makes up a grammar for
the language. EBNF also contains the following operators, which many
readers will recognize from regular expressions. Do not, however,
confuse them with "wildcard" characters, which have different meanings.
? Means that the preceding symbol (or group of symbols) is optional.
That is, it may appear once or not at all.
* Means that the preceding symbol (or group of symbols) may appear
zero or more times.
+ Means that the preceding symbol (or group of symbols) may appear
one or more times.
Parentheses may be used to group symbols together. For clarity, we will
use single quotes ('') to designate what is a verbatim character string
(as opposed to a symbol name).
Aliases
There are four kinds of aliases: User_Alias, Runas_Alias, Host_Alias and
Cmnd_Alias. Beginning with sudo 1.9.0, Cmd_Alias may be used in place of
Cmnd_Alias if desired.
Alias ::= 'User_Alias' User_Alias_Spec (':' User_Alias_Spec)* |
'Runas_Alias' Runas_Alias_Spec (':' Runas_Alias_Spec)* |
'Host_Alias' Host_Alias_Spec (':' Host_Alias_Spec)* |
'Cmnd_Alias' Cmnd_Alias_Spec (':' Cmnd_Alias_Spec)* |
'Cmd_Alias' Cmnd_Alias_Spec (':' Cmnd_Alias_Spec)*
User_Alias ::= NAME
User_Alias_Spec ::= User_Alias '=' User_List
Runas_Alias ::= NAME
Runas_Alias_Spec ::= Runas_Alias '=' Runas_List
Host_Alias ::= NAME
Host_Alias_Spec ::= Host_Alias '=' Host_List
Cmnd_Alias ::= NAME
Cmnd_Alias_Spec ::= Cmnd_Alias '=' Cmnd_List
NAME ::= [A-Z]([A-Z][0-9]_)*
Each alias definition is of the form
Alias_Type NAME = item1, item2, ...
where Alias_Type is one of User_Alias, Runas_Alias, Host_Alias, or
Cmnd_Alias. A NAME is a string of uppercase letters, numbers, and
underscore characters (`_'). A NAME must start with an uppercase letter.
It is possible to put several alias definitions of the same type on a
single line, joined by a colon (`:'). For example:
Alias_Type NAME = item1, item2, item3 : NAME = item4, item5
It is a syntax error to redefine an existing alias. It is possible to
use the same name for aliases of different types, but this is not
recommended.
The definitions of what constitutes a valid alias member follow.
User_List ::= User |
User ',' User_List
User ::= '!'* user name |
'!'* #user-ID |
'!'* %group |
'!'* %#group-ID |
'!'* +netgroup |
'!'* %:nonunix_group |
'!'* %:#nonunix_gid |
'!'* User_Alias
A User_List is made up of one or more user names, user-IDs (prefixed with
`#'), system group names and IDs (prefixed with `%' and `%#'
respectively), netgroups (prefixed with `+'), non-Unix group names and
IDs (prefixed with `%:' and `%:#' respectively), and User_Aliases. Each
list item may be prefixed with zero or more `!' operators. An odd number
of `!' operators negate the value of the item; an even number just cancel
each other out. User netgroups are matched using the user and domain
members only; the host member is not used when matching.
A user name, user-ID, group, group-ID, netgroup, nonunix_group or
nonunix_gid may be enclosed in double quotes to avoid the need for
escaping special characters. Alternately, special characters may be
specified in escaped hex mode, e.g., \x20 for space. When using double
quotes, any prefix characters must be included inside the quotes.
The actual nonunix_group and nonunix_gid syntax depends on the underlying
group provider plugin. For instance, the QAS AD plugin supports the
following formats:
o Group in the same domain: "%:Group Name"
o Group in any domain: "%:Group Name@FULLY.QUALIFIED.DOMAIN"
o Group SID: "%:S-1-2-34-5678901234-5678901234-5678901234-567"
See GROUP PROVIDER PLUGINS for more information.
Quotes around group names are optional. Unquoted strings must use a
backslash (`\') to escape spaces and special characters. See Other
special characters and reserved words for a list of characters that need
to be escaped.
Runas_List ::= Runas_Member |
Runas_Member ',' Runas_List
Runas_Member ::= '!'* user name |
'!'* #user-ID |
'!'* %group |
'!'* %#group-ID |
'!'* %:nonunix_group |
'!'* %:#nonunix_gid |
'!'* +netgroup |
'!'* Runas_Alias |
'!'* ALL
A Runas_List is similar to a User_List except that instead of
User_Aliases it can contain Runas_Aliases. User names and groups are
matched as strings. In other words, two users (groups) with the same
user (group) ID are considered to be distinct. If you wish to match all
user names with the same user-ID (e.g., root and toor), you can use a
user-ID instead of a name (#0 in the example given). The user-ID or
group-ID specified in a Runas_Member need not be listed in the password
or group database.
Host_List ::= Host |
Host ',' Host_List
Host ::= '!'* host name |
'!'* ip_addr |
'!'* network(/netmask)? |
'!'* +netgroup |
'!'* Host_Alias |
'!'* ALL
A Host_List is made up of one or more host names, IP addresses, network
numbers, netgroups (prefixed with `+'), and other aliases. Again, the
value of an item may be negated with the `!' operator. Host netgroups
are matched using the host (both qualified and unqualified) and domain
members only; the user member is not used when matching. If you specify
a network number without a netmask, sudo will query each of the local
host's network interfaces and, if the network number corresponds to one
of the hosts's network interfaces, will use the netmask of that
interface. The netmask may be specified either in standard IP address
notation (e.g., 255.255.255.0 or ffff:ffff:ffff:ffff::), or CIDR notation
(number of bits, e.g., 24 or 64). A host name may include shell-style
wildcards (see the Wildcards section below), but unless the hostname
command on your machine returns the fully qualified host name, you'll
need to use the fqdn flag for wildcards to be useful. sudo only inspects
actual network interfaces; this means that IP address 127.0.0.1
(localhost) will never match. Also, the host name "localhost" will only
match if that is the actual host name, which is usually only the case for
non-networked systems.
digest ::= [A-Fa-f0-9]+ |
[A-Za-z0-9\+/=]+
Digest_Spec ::= "sha224" ':' digest |
"sha256" ':' digest |
"sha384" ':' digest |
"sha512" ':' digest
Digest_List ::= Digest_Spec |
Digest_Spec ',' Digest_List
Cmnd_List ::= Cmnd |
Cmnd ',' Cmnd_List
command name ::= regex |
file name
command ::= command name |
command name args |
command name regex |
command name '""' |
ALL
Edit_Spec ::= "sudoedit" file name+ |
"sudoedit" regex |
"sudoedit"
List_Spec ::= "list"
Cmnd ::= Digest_List? '!'* command |
'!'* directory |
'!'* Edit_Spec |
'!'* List_Spec |
'!'* Cmnd_Alias
A Cmnd_List is a list of one or more commands, directories, or aliases.
A command is a fully qualified file name, which may include shell-style
wildcards (see the Wildcards section below), or a regular expression that
starts with `^' and ends with `$' (see the Regular expressions section
below). A directory is a fully qualified path name ending in a `/'.
When you specify a directory in a Cmnd_List, the user will be able to run
any file within that directory (but not in any sub-directories therein).
If no command line arguments are specified, the user may run the command
with any arguments they choose. Command line arguments can include
wildcards or be a regular expression that starts with `^' and ends with
`$'. If the command line arguments consist of `""', the command may only
be run with no arguments.
If a Cmnd has associated command line arguments, the arguments in the
Cmnd must match those given by the user on the command line. If the
arguments in a Cmnd begin with the `^' character, they will be
interpreted as a regular expression and matched accordingly. Otherwise,
shell-style wildcards are used when matching. Unless a regular
expression is specified, the following characters must be escaped with a
`\' if they are used in command arguments: `,', `:', `=', `\'. To
prevent arguments in a Cmnd that begin with a `^' character from being
interpreted as a regular expression, the `^' must be escaped with a `\'.
There are two commands built into sudo itself: "list" and "sudoedit".
Unlike other commands, these two must be specified in the sudoers file
without a leading path.
The "list" built-in can be used to permit a user to list another user's
privileges with sudo's -U option. For example, "sudo -l -U otheruser".
A user with the "list" privilege is able to list another user's
privileges even if they don't have permission to run commands as that
user. By default, only root or a user with the ability to run any
command as either root or the specified user on the current host may use
the -U option. No command line arguments may be specified with the
"list" built-in.
The "sudoedit" built-in is used to permit a user to run sudo with the -e
option (or as sudoedit). It may take command line arguments just as a
normal command does. Unlike other commands, "sudoedit" is built into
sudo itself and must be specified in the sudoers file without a leading
path. If a leading path is present, for example /usr/bin/sudoedit, the
path name will be silently converted to "sudoedit". A fully-qualified
path for sudoedit is treated as an error by visudo.
A command may be preceded by a Digest_List, a comma-separated list of one
or more Digest_Spec entries. If a Digest_List is present, the command
will only match successfully if it can be verified using one of the SHA-2
digests in the list. Starting with version 1.9.0, the ALL reserved word
can be used in conjunction with a Digest_List. The following digest
formats are supported: sha224, sha256, sha384, and sha512. The string
may be specified in either hex or base64 format (base64 is more compact).
There are several utilities capable of generating SHA-2 digests in hex
format such as openssl, shasum, sha224sum, sha256sum, sha384sum,
sha512sum.
For example, using openssl:
$ openssl dgst -sha224 /bin/ls
SHA224(/bin/ls)= 118187da8364d490b4a7debbf483004e8f3e053ec954309de2c41a25
It is also possible to use openssl to generate base64 output:
$ openssl dgst -binary -sha224 /bin/ls | openssl base64
EYGH2oNk1JC0p9679IMATo8+BT7JVDCd4sQaJQ==
Warning, if the user has write access to the command itself (directly or
via a sudo command), it may be possible for the user to replace the
command after the digest check has been performed but before the command
is executed. A similar race condition exists on systems that lack the
fexecve(2) system call when the directory in which the command is located
is writable by the user. See the description of the fdexec setting for
more information on how sudo executes commands that have an associated
digest.
Command digests are only supported by version 1.8.7 or higher.
Defaults
Certain configuration options may be changed from their default values at
run-time via one or more Default_Entry lines. These may affect all users
on any host (`Defaults'), all users on a specific host (`Defaults@host'),
a specific user (`Defaults:user'), a specific command (`Defaults!cmnd'),
or commands being run as a specific user (`Defaults>runasuser').
White space is not permitted between `Defaults' and the `@', `:', `!', or
`>' characters. While a comma-separated list may be used in place of a
single value after the `@', `:', `!', or `>' character, using an alias
instead of a list is often improve readability. Per-command entries may
not include command line arguments. If you need to specify arguments,
define a Cmnd_Alias and reference that instead.
Default_Type ::= 'Defaults' |
'Defaults@' Host_List |
'Defaults:' User_List |
'Defaults!' Cmnd_List |
'Defaults>' Runas_List
Default_Entry ::= Default_Type Parameter_List
Parameter_List ::= Parameter |
Parameter ',' Parameter_List
Parameter ::= Parameter '=' Value |
Parameter '+=' Value |
Parameter '-=' Value |
'!'* Parameter
Parameters may be flags, integer values, strings, or lists. Flags are
implicitly boolean and can be turned off via the `!' operator. Some
integer, string and list parameters may also be used in a boolean context
to disable them. Values may be enclosed in double quotes ("") when they
contain multiple words. Special characters may be escaped with a
backslash (`\').
To include a literal backslash character in a command line argument you
must escape the backslash twice. For example, to match `\n' as part of a
command line argument, you must use `\\\\n' in the sudoers file. This is
due to there being two levels of escaping, one in the sudoers parser
itself and another when command line arguments are matched by the
fnmatch(3) or regexec(3) function.
Lists have two additional assignment operators, `+=' and `-='. These
operators are used to add to and delete from a list respectively. It is
not an error to use the `-=' operator to remove an element that does not
exist in a list.
Defaults entries are parsed in the following order: global, host, user,
and runas Defaults first, then command defaults. If there are multiple
Defaults settings of the same type, the last matching setting is used.
The following Defaults settings are parsed before all others since they
may affect subsequent entries: fqdn, group_plugin, runas_default,
sudoers_locale.
See SUDOERS OPTIONS for a list of supported Defaults parameters.
User specification
User_Spec ::= User_List Host_List '=' Cmnd_Spec_List \
(':' Host_List '=' Cmnd_Spec_List)*
Cmnd_Spec_List ::= Cmnd_Spec |
Cmnd_Spec ',' Cmnd_Spec_List
Cmnd_Spec ::= Runas_Spec? Option_Spec* (Tag_Spec ':')* Cmnd
Runas_Spec ::= '(' Runas_List? (':' Runas_List)? ')'
Option_Spec ::= (Date_Spec | Timeout_Spec | Chdir_Spec | Chroot_Spec)
Date_Spec ::= ('NOTBEFORE=timestamp' | 'NOTAFTER=timestamp')
Timeout_Spec ::= 'TIMEOUT=timeout'
Chdir_Spec ::= 'CWD=directory'
Chroot_Spec ::= 'CHROOT=directory'
Tag_Spec ::= ('EXEC' | 'NOEXEC' | 'FOLLOW' | 'NOFOLLOW' |
'LOG_INPUT' | 'NOLOG_INPUT' | 'LOG_OUTPUT' |
'NOLOG_OUTPUT' | 'MAIL' | 'NOMAIL' | 'INTERCEPT' |
'NOINTERCEPT' | 'PASSWD' | 'NOPASSWD' | 'SETENV' |
'NOSETENV')
A user specification determines which commands a user may run (and as
what user) on specified hosts. By default, commands are run as root
(unless runas_default has been set to a different value) but this can
also be changed on a per-command basis.
The basic structure of a user specification is "who where = (as_whom)
what". Let's break that down into its constituent parts:
Runas_Spec
A Runas_Spec determines the user and/or the group that a command may be
run as. A fully-specified Runas_Spec consists of two Runas_Lists (as
defined above) separated by a colon (`:') and enclosed in a set of
parentheses. The first Runas_List indicates which users the command may
be run as via the -u option. The second defines a list of groups that
may be specified via the -g option (in addition to any of the target
user's groups). If both Runas_Lists are specified, the command may be
run with any combination of users and groups listed in their respective
Runas_Lists. If only the first is specified, the command may be run as
any user in the list and, optionally, with any group the target user
belongs to. If the first Runas_List is empty but the second is
specified, the command may be run as the invoking user with the group set
to any listed in the Runas_List. If both Runas_Lists are empty, the
command may only be run as the invoking user and the group, if specified,
must be one that the invoking user is a member of. If no Runas_Spec is
specified, the command may only be run as the runas_default user (root by
default) and the group, if specified, must be one that the runas_default
user is a member of.
A Runas_Spec sets the default for the commands that follow it. What this
means is that for the entry:
dgb boulder = (operator) /bin/ls, /bin/kill, /usr/bin/lprm
The user dgb may run /bin/ls, /bin/kill, and /usr/bin/lprm on the host
boulder--but only as operator. For example:
$ sudo -u operator /bin/ls
It is also possible to override a Runas_Spec later on in an entry. If we
modify the entry like so:
dgb boulder = (operator) /bin/ls, (root) /bin/kill, /usr/bin/lprm
Then user dgb is now allowed to run /bin/ls as operator, but /bin/kill
and /usr/bin/lprm as root.
We can extend this to allow dgb to run /bin/ls with either the user or
group set to operator:
dgb boulder = (operator : operator) /bin/ls, (root) /bin/kill,\
/usr/bin/lprm
While the group portion of the Runas_Spec permits the user to run as
command with that group, it does not force the user to do so. If no
group is specified on the command line, the command will run with the
group listed in the target user's password database entry. The following
would all be permitted by the sudoers entry above:
$ sudo -u operator /bin/ls
$ sudo -u operator -g operator /bin/ls
$ sudo -g operator /bin/ls
In the following example, user tcm may run commands that access a modem
device file with the dialer group.
tcm boulder = (:dialer) /usr/bin/tip, /usr/bin/cu,\
/usr/local/bin/minicom
In this example only the group will be set, the command still runs as
user tcm. For example:
$ sudo -g dialer /usr/bin/cu
Multiple users and groups may be present in a Runas_Spec, in which case
the user may select any combination of users and groups via the -u and -g
options. In this example:
alan ALL = (root, bin : operator, system) ALL
user alan may run any command as either user root or bin, optionally
setting the group to operator or system.
Option_Spec
A Cmnd may have zero or more options associated with it. Options may
consist of start and/or end dates and command timeouts. Once an option
is set for a Cmnd, subsequent Cmnds in the Cmnd_Spec_List, inherit that
option unless it is overridden by another option. Option names are
reserved words in sudoers. This means that none of the valid option
names (see below) can be used when declaring an alias.
Date_Spec
sudoers rules can be specified with a start and end date via the
NOTBEFORE and NOTAFTER settings. The time stamp must be specified in
"Generalized Time" as defined by RFC 4517. The format is effectively
`yyyymmddHHMMSSZ' where the minutes and seconds are optional. The `Z'
suffix indicates that the time stamp is in Coordinated Universal Time
(UTC). It is also possible to specify a timezone offset from UTC in
hours and minutes instead of a `Z'. For example, `-0500' would
correspond to Eastern Standard time in the US. As an extension, if no
`Z' or timezone offset is specified, local time will be used.
The following are all valid time stamps:
20170214083000Z
2017021408Z
20160315220000-0500
20151201235900
Timeout_Spec
A command may have a timeout associated with it. If the timeout expires
before the command has exited, the command will be terminated. The
timeout may be specified in combinations of days, hours, minutes, and
seconds with a single-letter case-insensitive suffix that indicates the
unit of time. For example, a timeout of 7 days, 8 hours, 30 minutes, and
10 seconds would be written as `7d8h30m10s'. If a number is specified
without a unit, seconds are assumed. Any of the days, minutes, hours, or
seconds may be omitted. The order must be from largest to smallest unit
and a unit may not be specified more than once.
The following are all valid timeout values: `7d8h30m10s', `14d', `8h30m',
`600s', `3600'. The following are invalid timeout values: `12m2w1d',
`30s10m4h', `1d2d3h'.
This setting is only supported by version 1.8.20 or higher.
Chdir_Spec
The working directory that the command will be run in can be specified
using the CWD setting. The directory must be a fully-qualified path name
beginning with a `/' or `~' character, or the special value "*". A value
of "*" indicates that the user may specify the working directory by
running sudo with the -D option. By default, commands are run from the
invoking user's current working directory, unless the -i option is given.
Path names of the form ~user/path/name are interpreted as being relative
to the named user's home directory. If the user name is omitted, the
path will be relative to the runas user's home directory.
This setting is only supported by version 1.9.3 or higher.
Chroot_Spec
The root directory that the command will be run in can be specified using
the CHROOT setting. The directory must be a fully-qualified path name
beginning with a `/' or `~' character, or the special value "*". A value
of "*" indicates that the user may specify the root directory by running
sudo with the -R option. This setting can be used to run the command in
a chroot(2) "sandbox" similar to the chroot(8) utility. Path names of
the form ~user/path/name are interpreted as being relative to the named
user's home directory. If the user name is omitted, the path will be
relative to the runas user's home directory.
This setting is only supported by version 1.9.3 or higher.
Tag_Spec
A command may have zero or more tags associated with it. The following
tag values are supported: EXEC, NOEXEC, FOLLOW, NOFOLLOW, LOG_INPUT,
NOLOG_INPUT, LOG_OUTPUT, NOLOG_OUTPUT, MAIL, NOMAIL, INTERCEPT,
NOINTERCEPT, PASSWD, NOPASSWD, SETENV, and NOSETENV. Once a tag is set
on a Cmnd, subsequent Cmnds in the Cmnd_Spec_List, inherit the tag unless
it is overridden by the opposite tag (in other words, PASSWD overrides
NOPASSWD and NOEXEC overrides EXEC).
EXEC and NOEXEC
If sudo has been compiled with noexec support and the underlying
operating system supports it, the NOEXEC tag can be used to prevent a
dynamically-linked executable from running further commands itself.
In the following example, user aaron may run /usr/bin/more and
/usr/bin/vi on the host shanty, but shell escapes will be disabled.
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
See the Preventing shell escapes section below for more details on how
NOEXEC works and whether or not it will work on your system.
FOLLOW and NOFOLLOW
Starting with version 1.8.15, sudoedit will not open a file that is a
symbolic link unless the sudoedit_follow flag is enabled. The FOLLOW
and NOFOLLOW tags override the value of sudoedit_follow and can be used
to permit (or deny) the editing of symbolic links on a per-command
basis. These tags are only effective for the sudoedit command and are
ignored for all other commands.
LOG_INPUT and NOLOG_INPUT
These tags override the value of the log_input flag on a per-command
basis. For more information, see I/O LOGGING.
LOG_OUTPUT and NOLOG_OUTPUT
These tags override the value of the log_output flag on a per-command
basis. For more information, see I/O LOGGING.
MAIL and NOMAIL
These tags provide fine-grained control over whether mail will be sent
when a user runs a command by overriding the value of the
mail_all_cmnds flag on a per-command basis. They have no effect when
sudo is run with the -l or -v options. A NOMAIL tag will also override
the mail_always and mail_no_perms options. For more information, see
the descriptions of mail_all_cmnds, mail_always, and mail_no_perms in
the SUDOERS OPTIONS section below.
PASSWD and NOPASSWD
By default, sudo requires that a user authenticate before running a
command. This behavior can be modified via the NOPASSWD tag. Like a
Runas_Spec, the NOPASSWD tag sets a default for the commands that
follow it in the Cmnd_Spec_List. Conversely, the PASSWD tag can be
used to reverse things. For example:
ray rushmore = NOPASSWD: /bin/kill, /bin/ls, /usr/bin/lprm
would allow the user ray to run /bin/kill, /bin/ls, and /usr/bin/lprm
as root on the machine "rushmore" without authenticating himself. If
we only want ray to be able to run /bin/kill without a password the
entry would be:
ray rushmore = NOPASSWD: /bin/kill, PASSWD: /bin/ls, /usr/bin/lprm
Note, however, that the PASSWD tag has no effect on users who are in
the group specified by the exempt_group setting.
By default, if the NOPASSWD tag is applied to any of a user's entries
for the current host, the user will be able to run `sudo -l' without a
password. Additionally, a user may only run `sudo -v' without a
password if all of the user's entries for the current host have the
NOPASSWD tag. This behavior may be overridden via the verifypw and
listpw options.
SETENV and NOSETENV
These tags override the value of the setenv flag on a per-command
basis. If SETENV has been set for a command, the user may disable the
env_reset flag from the command line via the -E option. Additionally,
environment variables set on the command line are not subject to the
restrictions imposed by env_check, env_delete, or env_keep. As such,
only trusted users should be allowed to set variables in this manner.
If the command matched is ALL, the SETENV tag is implied for that
command; this default may be overridden by use of the NOSETENV tag.
INTERCEPT and NOINTERCEPT
If sudo has been compiled with intercept support and the underlying
operating system supports it, the INTERCEPT tag can be used to cause
programs spawned by a command to be validated against sudoers and
logged just like they would be if run through sudo directly. This is
useful in conjunction with commands that allow shell escapes such as
editors, shells, and paginators. There is additional overhead due to
the policy check that may add latency when running commands such as
shell scripts that execute a large number of sub-commands. For
interactive commands, such as a shell or editor, the overhead is not
usually noticeable.
In the following example, user chuck may run any command on the machine
"research" in intercept mode.
chuck research = INTERCEPT: ALL
See the Preventing shell escapes section below for more details on how
INTERCEPT works and whether or not it will work on your system.
Wildcards
sudo allows shell-style wildcards (aka meta or glob characters) to be
used in host names, path names, and command line arguments in the sudoers
file. Wildcard matching is done via the glob(3) and fnmatch(3) functions
as specified by IEEE Std 1003.1 ("POSIX.1").
* Matches any set of zero or more characters (including white
space).
? Matches any single character (including white space).
[...] Matches any character in the specified range.
[!...] Matches any character not in the specified range.
\x For any character `x', evaluates to `x'. This is used to escape
special characters such as: `*', `?', `[', and `]'.
These are not regular expressions. Unlike a regular expression there is
no way to match one or more characters within a range.
Character classes may be used if your system's glob(3) and fnmatch(3)
functions support them. However, because the `:' character has special
meaning in sudoers, it must be escaped. For example:
/bin/ls [[\:alpha\:]]*
Would match any file name beginning with a letter.
A forward slash (`/') will not be matched by wildcards used in the file
name portion of the command. This is to make a path like:
/usr/bin/*
match /usr/bin/who but not /usr/bin/X11/xterm.
When matching the command line arguments, however, a slash does get
matched by wildcards since command line arguments may contain arbitrary
strings and not just path names.
Wildcards in command line arguments should be used with care.
Wildcards can match any character, including white space. In most cases,
it is safer to use a regular expression to match command line arguments.
For more information, see Wildcards in command arguments below.
Exceptions to wildcard rules
The following exceptions apply to the above rules:
"" If the empty string `""' is the only command line argument in
the sudoers file entry it means that command is not allowed to
be run with any arguments.
sudoedit Command line arguments to the sudoedit built-in command should
always be path names, so a forward slash (`/') will not be
matched by a wildcard.
Regular expressions
Starting with version 1.9.10, it is possible to use regular expressions
for path names and command line arguments. Regular expressions are more
expressive than shell-style wildcards and are usually safer because they
provide a greater degree of control when matching. The type of regular
expressions supported by sudoers are POSIX extended regular expressions,
similar to those used by the egrep(1) utility. They are usually
documented in the regex(7) or re_format(7) manual, depending on the
system. As an extension, if the regular expression begins with "(?i)",
it will be matched in a case-insensitive manner.
In sudoers, regular expressions must start with a `^' character and end
with a `$'. This makes it explicit what is, or is not, a regular
expression. Either the path name, the command line arguments or both may
be regular expressions. Because the path name and arguments are matched
separately, it is even possible to use wildcards for the path name and
regular expressions for the arguments. It is not possible to use a
single regular expression to match both the command and its arguments.
Regular expressions in sudoers are limited to 1024 characters.
There is no need to escape sudoers special characters in a regular
expression other than the pound sign (`#').
In the following example, user john can run the passwd(1) command as root
on any host but is not allowed to change root's password. This kind of
rule is impossible to express safely using wildcards.
john ALL = /usr/bin/passwd ^[a-zA-Z0-9_]+$,\
!/usr/bin/passwd root
It is also possible to use a regular expression in conjunction with
sudoedit rules. The following rule would give user bob the ability to
edit the /etc/motd, /etc/issue, and /etc/hosts files only.
bob ALL = sudoedit ^/etc/(motd|issue|hosts)$
Regular expressions may also be used to match the command itself. In
this example, a regular expression is used to allow user sid to run the
/usr/sbin/groupadd, /usr/sbin/groupmod, /usr/sbin/groupdel,
/usr/sbin/useradd, /usr/sbin/usermod, and /usr/sbin/userdel commands as
root.
sid ALL = ^/usr/sbin/(group|user)(add|mod|del)$
One disadvantage of using a regular expression to match the command name
is that it is not possible to match relative paths such as ./useradd or
../sbin/useradd. This has security implications when a regular
expression is used for the command name in conjunction with the negation
operator, `!', as such rules can be trivially bypassed. Because of this,
using a negated regular expression for the command name is strongly
discouraged. This does not apply to negated commands that only use a
regular expression to match the command arguments. See Regular
expressions in command names below for more information.
Including other files from within sudoers
It is possible to include other sudoers files from within the sudoers
file currently being parsed using the @include and @includedir
directives. For compatibility with sudo versions prior to 1.9.1,
#include and #includedir are also accepted.
An include file can be used, for example, to keep a site-wide sudoers
file in addition to a local, per-machine file. For the sake of this
example the site-wide sudoers file will be /etc/sudoers and the per-
machine one will be /etc/sudoers.local. To include /etc/sudoers.local
from within /etc/sudoers one would use the following line in
/etc/sudoers:
@include /etc/sudoers.local
When sudo reaches this line it will suspend processing of the current
file (/etc/sudoers) and switch to /etc/sudoers.local. Upon reaching the
end of /etc/sudoers.local, the rest of /etc/sudoers will be processed.
Files that are included may themselves include other files. A hard limit
of 128 nested include files is enforced to prevent include file loops.
Starting with version 1.9.1, the path to the include file may contain
white space if it is escaped with a backslash (`\'). Alternately, the
entire path may be enclosed in double quotes (""), in which case no
escaping is necessary. To include a literal backslash in the path, `\\'
should be used.
If the path to the include file is not fully-qualified (does not begin
with a `/'), it must be located in the same directory as the sudoers file
it was included from. For example, if /etc/sudoers contains the line:
@include sudoers.local
the file that will be included is /etc/sudoers.local.
The file name may also include the `%h' escape, signifying the short form
of the host name. In other words, if the machine's host name is
"xerxes", then
@include /etc/sudoers.%h
will cause sudo to include the file /etc/sudoers.xerxes. Any path name
separator characters (`/') present in the host name will be replaced with
an underbar (`_') during expansion.
The @includedir directive can be used to create a sudoers.d directory
that the system package manager can drop sudoers file rules into as part
of package installation. For example, given:
@includedir /etc/sudoers.d
sudo will suspend processing of the current file and read each file in
/etc/sudoers.d, skipping file names that end in `~' or contain a `.'
character to avoid causing problems with package manager or editor
temporary/backup files.
Files are parsed in sorted lexical order. That is,
/etc/sudoers.d/01_first will be parsed before /etc/sudoers.d/10_second.
Be aware that because the sorting is lexical, not numeric,
/etc/sudoers.d/1_whoops would be loaded after /etc/sudoers.d/10_second.
Using a consistent number of leading zeroes in the file names can be used
to avoid such problems. After parsing the files in the directory,
control returns to the file that contained the @includedir directive.
Unlike files included via @include, visudo will not edit the files in a
@includedir directory unless one of them contains a syntax error. It is
still possible to run visudo with the -f flag to edit the files directly,
but this will not catch the redefinition of an alias that is also present
in a different file.
Other special characters and reserved words
The pound sign (`#') is used to indicate a comment (unless it is part of
a #include directive or unless it occurs in the context of a user name
and is followed by one or more digits, in which case it is treated as a
user-ID). Both the comment character and any text after it, up to the
end of the line, are ignored.
The reserved word ALL is a built-in alias that always causes a match to
succeed. It can be used wherever one might otherwise use a Cmnd_Alias,
User_Alias, Runas_Alias, or Host_Alias. Attempting to define an alias
named ALL will result in a syntax error. Using ALL can be dangerous
since in a command context, it allows the user to run any command on the
system.
The following option names permitted in an Option_Spec are also
considered reserved words: CHROOT, TIMEOUT, CWD, NOTBEFORE and NOTAFTER.
Attempting to define an alias with the same name as one of the options
will result in a syntax error.
An exclamation point (`!') can be used as a logical not operator in a
list or alias as well as in front of a Cmnd. This allows one to exclude
certain values. For the `!' operator to be effective, there must be
something for it to exclude. For example, to match all users except for
root one would use:
ALL, !root
If the ALL, is omitted, as in:
!root
it would explicitly deny root but not match any other users. This is
different from a true "negation" operator.
Note, however, that using a `!' in conjunction with the built-in ALL
alias to allow a user to run "all but a few" commands rarely works as
intended (see SECURITY NOTES below).
Long lines can be continued with a backslash (`\') as the last character
on the line.
White space between elements in a list as well as special syntactic
characters in a User Specification (`=', `:', `(', `)') is optional.
The following characters must be escaped with a backslash (`\') when used
as part of a word (e.g., a user name or host name): `!', `=', `:', `,',
`(', `)', `\'.
SUDOERS OPTIONS
sudo's behavior can be modified by Default_Entry lines, as explained
earlier. A list of all supported Defaults parameters, grouped by type,
are listed below.
Boolean Flags:
always_query_group_plugin
If a group_plugin is configured, use it to resolve
groups of the form `%group' as long as there is not
also a system group of the same name. Normally, only
groups of the form `%:group' are passed to the
group_plugin. This flag is off by default.
always_set_home If enabled, sudo will set the HOME environment variable
to the home directory of the target user (which is the
runas_default user unless the -u option is used). This
flag is largely obsolete and has no effect unless the
env_reset flag has been disabled or HOME is present in
the env_keep list, both of which are strongly
discouraged. This flag is off by default.
authenticate If set, users must authenticate themselves via a
password (or other means of authentication) before they
may run commands. This default may be overridden via
the PASSWD and NOPASSWD tags. This flag is on by
default.
case_insensitive_group
If enabled, group names in sudoers will be matched in a
case insensitive manner. This may be necessary when
users are stored in LDAP or AD. This flag is on by
default.
case_insensitive_user
If enabled, user names in sudoers will be matched in a
case insensitive manner. This may be necessary when
groups are stored in LDAP or AD. This flag is on by
default.
closefrom_override
If set, the user may use the -C option which overrides
the default starting point at which sudo begins closing
open file descriptors. This flag is off by default.
compress_io If set, and sudo is configured to log a command's input
or output, the I/O logs will be compressed using zlib.
This flag is on by default when sudo is compiled with
zlib support.
exec_background By default, sudo runs a command as the foreground
process as long as sudo itself is running in the
foreground. When the exec_background flag is enabled
and the command is being run in a pseudo-terminal (due
to I/O logging or the use_pty flag), the command will
be run as a background process. Attempts to read from
the controlling terminal (or to change terminal
settings) will result in the command being suspended
with the SIGTTIN signal (or SIGTTOU in the case of
terminal settings). If this happens when sudo is a
foreground process, the command will be granted the
controlling terminal and resumed in the foreground with
no user intervention required. The advantage of
initially running the command in the background is that
sudo need not read from the terminal unless the command
explicitly requests it. Otherwise, any terminal input
must be passed to the command, whether it has required
it or not (the kernel buffers terminals so it is not
possible to tell whether the command really wants the
input). This is different from historic sudo behavior
or when the command is not being run in a pseudo-
terminal.
For this to work seamlessly, the operating system must
support the automatic restarting of system calls.
Unfortunately, not all operating systems do this by
default, and even those that do may have bugs. For
example, macOS fails to restart the tcgetattr(3) and
tcsetattr(3) functions (this is a bug in macOS).
Furthermore, because this behavior depends on the
command stopping with the SIGTTIN or SIGTTOU signals,
programs that catch these signals and suspend
themselves with a different signal (usually SIGTOP)
will not be automatically foregrounded. Some versions
of the linux su(1) command behave this way. This flag
is off by default.
This setting is only supported by version 1.8.7 or
higher. It has no effect unless I/O logging is enabled
or the use_pty flag is enabled.
env_editor If set, visudo will use the value of the SUDO_EDITOR,
VISUAL or EDITOR environment variables before falling
back on the default editor list. visudo is typically
run as root so this flag may allow a user with visudo
privileges to run arbitrary commands as root without
logging. An alternative is to place a colon-separated
list of "safe" editors int the editor setting. visudo
will then only use SUDO_EDITOR, VISUAL or EDITOR if
they match a value specified in editor. If the
env_reset flag is enabled, the SUDO_EDITOR, VISUAL
and/or EDITOR environment variables must be present in
the env_keep list for the env_editor flag to function
when visudo is invoked via sudo. This flag is on by
default.
env_reset If set, sudo will run the command in a minimal
environment containing the TERM, PATH, HOME, MAIL,
SHELL, LOGNAME, USER and SUDO_* variables. Any
variables in the caller's environment or in the file
specified by the restricted_env_file setting that match
the env_keep and env_check lists are then added,
followed by any variables present in the file specified
by the env_file setting (if any). The contents of the
env_keep and env_check lists, as modified by global
Defaults parameters in sudoers, are displayed when sudo
is run by root with the -V option. If the secure_path
setting is enabled, its value will be used for the PATH
environment variable. This flag is on by default.
fast_glob Normally, sudo uses the glob(3) function to do shell-
style globbing when matching path names. However,
since it accesses the file system, glob(3) can take a
long time to complete for some patterns, especially
when the pattern references a network file system that
is mounted on demand (auto mounted). The fast_glob
flag causes sudo to use the fnmatch(3) function, which
does not access the file system to do its matching.
The disadvantage of fast_glob is that it is unable to
match relative paths such as ./ls or ../bin/ls. This
has security implications when path names that include
globbing characters are used with the negation
operator, `!', as such rules can be trivially bypassed.
As such, this flag should not be used when the sudoers
file contains rules that contain negated path names
which include globbing characters. This flag is off by
default.
log_passwords Most programs that require a user's password will
disable echo before reading the password to avoid
displaying the plaintext password on the screen.
However, if terminal input is being logged (see I/O
LOGGING), the password will still be present in the I/O
log. If the log_passwords option is disabled, sudoers
will attempt to prevent passwords from being logged.
It does this by using the regular expressions in
passprompt_regex to match a password prompt in the
terminal output buffer. When a match is found, input
characters in the I/O log will be replaced with `*'
until either a line feed or carriage return is found in
the terminal input or a new terminal output buffer is
received. If, however, a program displays characters
as the user types (such as sudo when pwfeedback is
set), only the first character of the password will be
replaced in the I/O log. This option has no effect
unless log_input or log_ttyin are also set. This flag
is on by default.
This setting is only supported by version 1.9.10 or
higher.
fqdn Set this flag if you want to put fully qualified host
names in the sudoers file when the local host name (as
returned by the `hostname' command) does not contain
the domain name. In other words, instead of myhost you
would use myhost.mydomain.edu. You may still use the
short form if you wish (and even mix the two). This
flag is only effective when the "canonical" host name,
as returned by the getaddrinfo(3) or gethostbyname(3)
function, is a fully-qualified domain name. This is
usually the case when the system is configured to use
DNS for host name resolution.
If the system is configured to use the /etc/hosts file
in preference to DNS, the "canonical" host name may not
be fully-qualified. The order that sources are queried
for host name resolution is usually specified in the
/etc/nsswitch.conf, /etc/netsvc.conf, /etc/host.conf,
or, in some cases, /etc/resolv.conf file. In the
/etc/hosts file, the first host name of the entry is
considered to be the "canonical" name; subsequent names
are aliases that are not used by sudoers. For example,
the following hosts file line for the machine "xyzzy"
has the fully-qualified domain name as the "canonical"
host name, and the short version as an alias.
192.168.1.1 xyzzy.sudo.ws xyzzy
If the machine's hosts file entry is not formatted
properly, the fqdn flag will not be effective if it is
queried before DNS.
Beware that when using DNS for host name resolution,
turning on fqdn requires sudoers to make DNS lookups
which renders sudo unusable if DNS stops working (for
example if the machine is disconnected from the
network). Just like with the hosts file, you must use
the "canonical" name as DNS knows it. That is, you may
not use a host alias (CNAME entry) due to performance
issues and the fact that there is no way to get all
aliases from DNS.
This flag is off by default.
ignore_audit_errors
Allow commands to be run even if sudoers cannot write
to the audit log. If enabled, an audit log write
failure is not treated as a fatal error. If disabled,
a command may only be run after the audit event is
successfully written. This flag is only effective on
systems for which sudoers supports audit logging,
including FreeBSD, Linux, macOS, and Solaris. This
flag is on by default.
ignore_dot If set, sudo will ignore "." or "" (both denoting the
current directory) in the PATH environment variable;
the PATH itself is not modified. This flag is on by
default.
ignore_iolog_errors
Allow commands to be run even if sudoers cannot write
to the I/O log (local or remote). If enabled, an I/O
log write failure is not treated as a fatal error. If
disabled, the command will be terminated if the I/O log
cannot be written to. This flag is off by default.
ignore_logfile_errors
Allow commands to be run even if sudoers cannot write
to the log file. If enabled, a log file write failure
is not treated as a fatal error. If disabled, a
command may only be run after the log file entry is
successfully written. This flag only has an effect
when sudoers is configured to use file-based logging
via the logfile setting. This flag is on by default.
ignore_local_sudoers
If set via LDAP, parsing of /opt/local/etc/sudoers will
be skipped. This is intended for sites that wish to
prevent the usage of local sudoers files so that only
LDAP is used. This thwarts the efforts of rogue
operators who would attempt to add roles to
/opt/local/etc/sudoers. When this flag is enabled,
/opt/local/etc/sudoers does not even need to exist.
Since this flag tells sudo how to behave when no
specific LDAP entries have been matched, this
sudoOption is only meaningful for the `cn=defaults'
section. This flag is off by default.
ignore_unknown_defaults
If set, sudo will not produce a warning if it
encounters an unknown Defaults entry in the sudoers
file or an unknown sudoOption in LDAP. This flag is
off by default.
insults If set, sudo will insult users when they enter an
incorrect password. This flag is off by default.
log_allowed If set, sudoers will log commands allowed by the policy
to the system audit log (where supported) as well as to
syslog and/or a log file. This flag is on by default.
This setting is only supported by version 1.8.29 or
higher.
log_denied If set, sudoers will log commands denied by the policy
to the system audit log (where supported) as well as to
syslog and/or a log file. This flag is on by default.
This setting is only supported by version 1.8.29 or
higher.
log_exit_status If set, sudoers will log the exit value of commands
that are run to syslog and/or a log file. If a command
was terminated by a signal, the signal name is logged
as well. This flag is off by default.
This setting is only supported by version 1.9.8 or
higher.
log_host If set, the host name will be included in log entries
written to the file configured by the logfile setting.
This flag is off by default.
log_input If set, sudo will run the command in a pseudo-terminal
(if sudo was run from a terminal) and log all user
input. If the standard input is not connected to the
user's terminal, due to I/O redirection or because the
command is part of a pipeline, that input is also
logged. For more information about I/O logging, see
the I/O LOGGING section. This flag is off by default.
log_output If set, sudo will run the command in a pseudo-terminal
(if sudo was run from a terminal) and log all output
that is sent to the user's terminal, the standard
output or the standard error. If the standard output
or standard error is not connected to the user's
terminal, due to I/O redirection or because the command
is part of a pipeline, that output is also logged. For
more information about I/O logging, see the I/O LOGGING
section. This flag is off by default.
log_server_keepalive
If set, sudo will enable the TCP keepalive socket
option on the connection to the log server. This
enables the periodic transmission of keepalive messages
to the server. If the server does not respond to a
message, the connection will be closed and the running
command will be terminated unless the
ignore_iolog_errors flag (I/O logging enabled) or the
ignore_log_errors flag (I/O logging disabled) is set.
This flag is on by default.
This setting is only supported by version 1.9.0 or
higher.
log_server_verify
If set, the server certificate received during the TLS
handshake must be valid and it must contain either the
server name (from log_servers) or its IP address. If
either of these conditions is not met, the TLS
handshake will fail. This flag is on by default.
This setting is only supported by version 1.9.0 or
higher.
log_stderr If set, sudo will log the standard error if it is not
connected to the user's terminal. This can be used to
log output to a pipe or redirected to a file. This
flag is off by default but is enabled when either the
log_output flag or the LOG_OUTPUT command tag is set.
log_stdin If set, sudo will log the standard input if it is not
connected to the user's terminal. This can be used to
log input from a pipe or redirected from a file. This
flag is off by default but is enabled when either the
log_input flag or the LOG_INPUT command tag is set.
log_stdout If set, sudo will log the standard output if it is not
connected to the user's terminal. This can be used to
log output to a pipe or redirected to a file. This
flag is off by default but is enabled when either the
log_output flag or the LOG_OUTPUT command tag is set.
log_subcmds If set, sudoers will log when a command spawns a child
process and executes a program using the execve(2),
execl(3), execle(3), execlp(3), execv(3), execvp(3),
execvpe(3), or system(3) library functions. For
example, if a shell is run by sudo, the individual
commands run via the shell will be logged. This flag
is off by default.
The log_subcmds flag uses the same underlying mechanism
as the intercept setting. Some commands may not work
properly when log_subcmds is enabled, due to the way it
intercepts sub-commands. See Preventing shell escapes
for more information on what systems support this
option and its limitations. This setting is only
supported by version 1.9.8 or higher and is
incompatible with SELinux RBAC support unless the
system supports seccomp(2) filter mode.
log_ttyin If set, sudo will run the command in a pseudo-terminal
and log user keystrokes sent to the user's terminal, if
one is present. This flag is off by default but is
enabled when either the log_input flag or the LOG_INPUT
command tag is set. If no terminal is present, for
example when running a remote command using ssh(1),
this flag will have no effect.
log_ttyout If set, sudo will run the command in a pseudo-terminal
and log all output displayed on the user's terminal, if
one is present. This flag is off by default but is
enabled when either the log_output flag or the
LOG_OUTPUT command tag is set. If no terminal is
present, for example when running a remote command
using ssh(1), this flag will have no effect.
log_year If set, the four-digit year will be logged in the (non-
syslog) sudo log file. This flag is off by default.
long_otp_prompt When validating with a One Time Password (OTP) scheme
such as S/Key or OPIE, a two-line prompt is used to
make it easier to cut and paste the challenge to a
local window. It's not as pretty as the default but
some people find it more convenient. This flag is off
by default.
mail_all_cmnds Send mail to the mailto user every time a user attempts
to run a command via sudo (this includes sudoedit). No
mail will be sent if the user runs sudo with the -l or
-v option unless there is an authentication error and
the mail_badpass flag is also set. This flag is off by
default.
mail_always Send mail to the mailto user every time a user runs
sudo. This flag is off by default.
mail_badpass Send mail to the mailto user if the user running sudo
does not enter the correct password. If the command
the user is attempting to run is not permitted by
sudoers and one of the mail_all_cmnds, mail_always,
mail_no_host, mail_no_perms or mail_no_user flags are
set, this flag will have no effect. This flag is off
by default.
mail_no_host If set, mail will be sent to the mailto user if the
invoking user exists in the sudoers file, but is not
allowed to run commands on the current host. This flag
is off by default.
mail_no_perms If set, mail will be sent to the mailto user if the
invoking user is allowed to use sudo but the command
they are trying is not listed in their sudoers file
entry or is explicitly denied. This flag is off by
default.
mail_no_user If set, mail will be sent to the mailto user if the
invoking user is not in the sudoers file. This flag is
on by default.
match_group_by_gid
By default, sudoers will look up each group the user is
a member of by group-ID to determine the group name
(this is only done once). The resulting list of the
user's group names is used when matching groups listed
in the sudoers file. This works well on systems where
the number of groups listed in the sudoers file is
larger than the number of groups a typical user belongs
to. On systems where group lookups are slow, where
users may belong to a large number of groups, or where
the number of groups listed in the sudoers file is
relatively small, it may be prohibitively expensive and
running commands via sudo may take longer than normal.
On such systems it may be faster to use the
match_group_by_gid flag to avoid resolving the user's
group-IDs to group names. In this case, sudoers must
look up any group name listed in the sudoers file and
use the group-ID instead of the group name when
determining whether the user is a member of the group.
If match_group_by_gid is enabled, group database
lookups performed by sudoers will be keyed by group
name as opposed to group-ID. On systems where there
are multiple sources for the group database, it is
possible to have conflicting group names or group-IDs
in the local /etc/group file and the remote group
database. On such systems, enabling or disabling
match_group_by_gid can be used to choose whether group
database queries are performed by name (enabled) or ID
(disabled), which may aid in working around group entry
conflicts.
The match_group_by_gid flag has no effect when sudoers
data is stored in LDAP. This flag is off by default.
This setting is only supported by version 1.8.18 or
higher.
intercept If set, all commands run via sudo will behave as if the
INTERCEPT tag has been set, unless overridden by an
NOINTERCEPT tag. Some commands may not work properly
when intercept is enabled, due to the way it intercept
sub-commands. See the description of INTERCEPT and
NOINTERCEPT above as well as the Preventing shell
escapes section at the end of this manual. This flag
is off by default.
This setting is only supported by version 1.9.8 or
higher and is incompatible with SELinux RBAC support
unless the system supports seccomp(2) filter mode.
intercept_allow_setid
On most systems, the dynamic loader will ignore
LD_PRELOAD (or the equivalent) when running set-user-ID
and set-group-ID programs, effectively disabling
intercept mode. To prevent this from happening,
sudoers will not permit a set-user-ID or set-group-ID
program to be run in intercept mode unless
intercept_allow_setid is enable. This flag has no
effect unless the intercept flag is enabled or the
INTERCEPT tag has been set for the command. This flag
is on by default when the intercept_type option is set
to trace, otherwise it default to off.
This setting is only supported by version 1.9.8 or
higher.
intercept_authenticate
If set, commands run by an intercepted process must be
authenticated when the user's time stamp is not
current. For example, if a shell is run with intercept
enabled, as soon as the invoking user's time stamp is
out of date, subsequent commands will need to be
authenticated. This flag has no effect unless the
intercept flag is enabled or the INTERCEPT tag has been
set for the command. This flag is off by default.
This setting is only supported by version 1.9.8 or
higher.
intercept_verify If set, sudo will attempt to verify that a command run
in intercept mode has the expected path name, command
line arguments and environment.
The process will be stopped after execve(2) has
completed but before the new command has had a chance
to run. To verify the command, sudo will read the
command's path from /proc/PID/exe, the command line
arguments and environment from the process's memory,
and compare them against the arguments that were passed
to execve(2). In the event of a mismatch, the command
will be sent a SIGKILL signal and terminated.
This can help prevent a time of check versus time of
use issue with intercept mode where the execve(2)
arguments could be altered after the sudoers policy
check. The checks can only be performed if the proc(5)
file system is available. This flag has no effect
unless the intercept flag is enabled or the INTERCEPT
tag has been set for the command and the intercept_type
option is set to trace.
This setting is incompatible with programs that change
their root directory via chroot(2). If a program
changes its root directory, path names will no longer
match those seen by the sudo parent process and sub-
commands will be terminated before they have a chance
to run. This flag is on by default.
This setting is only supported by version 1.9.12 or
higher.
netgroup_tuple If set, netgroup lookups will be performed using the
full netgroup tuple: host name, user name, and domain
(if one is set). Historically, sudo only matched the
user name and domain for netgroups used in a User_List
and only matched the host name and domain for netgroups
used in a Host_List. This flag is off by default.
noexec If set, all commands run via sudo will behave as if the
NOEXEC tag has been set, unless overridden by an EXEC
tag. See the description of EXEC and NOEXEC above as
well as the Preventing shell escapes section at the end
of this manual. This flag is off by default.
noninteractive_auth
If set, authentication will be attempted even in non-
interactive mode (when sudo's -n option is specified).
This allows authentication methods that don't require
user interaction to succeed. Authentication methods
that require input from the user's terminal will still
fail. If disabled, authentication will not be
attempted in non-interactive mode. This flag is off by
default.
This setting is only supported by version 1.9.10 or
higher.
pam_acct_mgmt On systems that use PAM for authentication, sudo will
perform PAM account validation for the invoking user by
default. The actual checks performed depend on which
PAM modules are configured. If enabled, account
validation will be performed regardless of whether or
not a password is required. This flag is on by
default.
This setting is only supported by version 1.8.28 or
higher.
pam_rhost On systems that use PAM for authentication, sudo will
set the PAM remote host value to the name of the local
host when the pam_rhost flag is enabled. On Linux
systems, enabling pam_rhost may result in DNS lookups
of the local host name when PAM is initialized. On
Solaris versions prior to Solaris 8, pam_rhost must be
enabled if pam_ruser is also enabled to avoid a crash
in the Solaris PAM implementation.
This flag is off by default on systems other than
Solaris.
This setting is only supported by version 1.9.0 or
higher.
pam_ruser On systems that use PAM for authentication, sudo will
set the PAM remote user value to the name of the user
that invoked sudo when the pam_ruser flag is enabled.
This flag is on by default.
This setting is only supported by version 1.9.0 or
higher.
pam_session On systems that use PAM for authentication, sudo will
create a new PAM session for the command to be run in.
Unless sudo is given the -i or -s options, PAM session
modules are run with the "silent" flag enabled. This
prevents last login information from being displayed
for every command on some systems. Disabling
pam_session may be needed on older PAM implementations
or on operating systems where opening a PAM session
changes the utmp or wtmp files. If PAM session support
is disabled, resource limits may not be updated for the
command being run. If pam_session, pam_setcred, and
use_pty are disabled, log_servers has not been set and
I/O logging has not been configured, sudo will execute
the command directly instead of running it as a child
process. This flag is on by default.
This setting is only supported by version 1.8.7 or
higher.
pam_setcred On systems that use PAM for authentication, sudo will
attempt to establish credentials for the target user by
default, if supported by the underlying authentication
system. One example of a credential is a Kerberos
ticket. If pam_session, pam_setcred, and use_pty are
disabled, log_servers has not been set and I/O logging
has not been configured, sudo will execute the command
directly instead of running it as a child process.
This flag is on by default.
This setting is only supported by version 1.8.8 or
higher.
pam_silent If set, PAM authentication will be performed in silent
mode. This prevents PAM authentication modules from
generating output. In some cases, this may suppress
important information about why authentication failed.
For example, PAM modules such as pam_faillock will only
display a warning if pam_silent is disabled. This flag
is on by default.
This setting is only supported by version 1.8.16 or
higher.
passprompt_override
If set, the prompt specified by passprompt or the
SUDO_PROMPT environment variable will always be used
and will replace the prompt provided by a PAM module or
other authentication method. This flag is off by
default.
path_info Normally, sudo will tell the user when a command could
not be found in their PATH environment variable. Some
sites may wish to disable this as it could be used to
gather information on the location of executables that
the normal user does not have access to. The
disadvantage is that if the executable is simply not in
the user's PATH, sudo will tell the user that they are
not allowed to run it, which can be confusing. This
flag is on by default.
preserve_groups By default, sudo will initialize the group vector to
the list of groups the target user is in. When
preserve_groups is set, the user's existing group
vector is left unaltered. The real and effective
group-IDs, however, are still set to match the target
user. This flag is off by default.
pwfeedback By default, sudo reads the password like most other
Unix programs, by turning off echo until the user hits
the return (or enter) key. Some users become confused
by this as it appears to them that sudo has hung at
this point. When pwfeedback is set, sudo will provide
visual feedback when the user presses a key. This does
have a security impact as an onlooker may be able to
determine the length of the password being entered.
This flag is off by default.
requiretty If set, sudo will only run when the user is logged in
to a real tty. When this flag is set, sudo can only be
run from a login session and not via other means such
as cron(8) or cgi-bin scripts. This flag is off by
default.
root_sudo If set, root is allowed to run sudo too. Disabling
this prevents users from "chaining" sudo commands to
get a root shell by doing something like `sudo sudo
/bin/sh'. Note, however, that turning off root_sudo
will also prevent root from running sudoedit.
Disabling root_sudo provides no real additional
security; it exists purely for historical reasons.
This flag is on by default.
rootpw If set, sudo will prompt for the root password instead
of the password of the invoking user when running a
command or editing a file. This flag is off by
default.
runas_allow_unknown_id
If enabled, allow matching of runas user and group IDs
that are not present in the password or group
databases. In addition to explicitly matching unknown
user or group IDs in a Runas_List, this option also
allows the ALL alias to match unknown IDs. This flag
is off by default.
This setting is only supported by version 1.8.30 or
higher. Older versions of sudo always allowed matching
of unknown user and group IDs.
runas_check_shell
If enabled, sudo will only run commands as a user whose
shell appears in the /etc/shells file, even if the
invoking user's Runas_List would otherwise permit it.
If no /etc/shells file is present, a system-dependent
list of built-in default shells is used. On many
operating systems, system users such as "bin", do not
have a valid shell and this flag can be used to prevent
commands from being run as those users. This flag is
off by default.
This setting is only supported by version 1.8.30 or
higher.
runaspw If set, sudo will prompt for the password of the user
defined by the runas_default option (defaults to root)
instead of the password of the invoking user when
running a command or editing a file. This flag is off
by default.
set_home If enabled and sudo is invoked with the -s option, the
HOME environment variable will be set to the home
directory of the target user (which is the
runas_default user unless the -u option is used). This
flag is largely obsolete and has no effect unless the
env_reset flag has been disabled or HOME is present in
the env_keep list, both of which are strongly
discouraged. This flag is off by default.
set_logname Normally, sudo will set the LOGNAME and USER
environment variables to the name of the target user
(the user specified by runas_default unless the -u
option is given). However, since some programs
(including the RCS revision control system) use LOGNAME
to determine the real identity of the user, it may be
desirable to change this behavior. This can be done by
negating the set_logname option. The set_logname
option will have no effect if the env_reset option has
not been disabled and the env_keep list contains
LOGNAME or USER. This flag is on by default.
set_utmp When enabled, sudo will create an entry in the utmp (or
utmpx) file when a pseudo-terminal is allocated. A
pseudo-terminal is allocated by sudo when it is running
in a terminal and one or more of the log_input,
log_output, log_stdin, log_stdout, log_stderr,
log_ttyin, log_ttyout, or use_pty flags is enabled. By
default, the new entry will be a copy of the user's
existing utmp entry (if any), with the tty, time, type,
and pid fields updated. This flag is on by default.
setenv Allow the user to disable the env_reset option from the
command line via the -E option. Additionally,
environment variables set via the command line are not
subject to the restrictions imposed by env_check,
env_delete, or env_keep. As such, only trusted users
should be allowed to set variables in this manner.
This flag is off by default.
shell_noargs If set and sudo is invoked with no arguments it acts as
if the -s option had been given. That is, it runs a
shell as root (the shell is determined by the SHELL
environment variable if it is set, falling back on the
shell listed in the invoking user's /etc/passwd entry
if not). This flag is off by default.
stay_setuid Normally, when sudo executes a command the real and
effective user-IDs are set to the target user (root by
default). This option changes that behavior such that
the real user-ID is left as the invoking user's user-
ID. In other words, this makes sudo act as a set-user-
ID wrapper. This can be useful on systems that disable
some potentially dangerous functionality when a program
is run set-user-ID. This option is only effective on
systems that support either the setreuid(2) or
setresuid(2) system call. This flag is off by default.
sudoedit_checkdir
If set, sudoedit will check all directory components of
the path to be edited for writability by the invoking
user. Symbolic links will not be followed in writable
directories and sudoedit will refuse to edit a file
located in a writable directory. These restrictions
are not enforced when sudoedit is run by root. On some
systems, if all directory components of the path to be
edited are not readable by the target user, sudoedit
will be unable to edit the file. This flag is on by
default.
This setting was first introduced in version 1.8.15 but
initially suffered from a race condition. The check
for symbolic links in writable intermediate directories
was added in version 1.8.16.
sudoedit_follow By default, sudoedit will not follow symbolic links
when opening files. The sudoedit_follow option can be
enabled to allow sudoedit to open symbolic links. It
may be overridden on a per-command basis by the FOLLOW
and NOFOLLOW tags. This flag is off by default.
This setting is only supported by version 1.8.15 or
higher.
syslog_pid When logging via syslog(3), include the process ID in
the log entry. This flag is off by default.
This setting is only supported by version 1.8.21 or
higher.
targetpw If set, sudo will prompt for the password of the user
specified by the -u option (defaults to the value of
runas_default) instead of the password of the invoking
user when running a command or editing a file. This
flag precludes the use of a user-ID not listed in the
passwd database as an argument to the -u option. This
flag is off by default.
tty_tickets If set, users must authenticate on a per-tty basis.
With this flag enabled, sudo will use a separate record
in the time stamp file for each terminal. If disabled,
a single record is used for all login sessions.
This option has been superseded by the timestamp_type
option.
umask_override If set, sudo will set the umask as specified in the
sudoers file without modification. This makes it
possible to specify a umask in the sudoers file that is
more permissive than the user's own umask and matches
historical behavior. If umask_override is not set,
sudo will set the umask to be the union of the user's
umask and what is specified in sudoers. This flag is
off by default.
use_netgroups If set, netgroups (prefixed with `+'), may be used in
place of a user or host. For LDAP-based sudoers,
netgroup support requires an expensive sub-string match
on the server unless the NETGROUP_BASE directive is
present in the /etc/ldap.conf file. If netgroups are
not needed, this option can be disabled to reduce the
load on the LDAP server. This flag is on by default.
use_pty If set, and sudo is running in a terminal, the command
will be run in a new pseudo-terminal. If the sudo
process is not attached to a terminal, use_pty has no
effect.
A malicious program run under sudo may be capable of
injecting commands into the user's terminal or running
a background process that retains access to the user's
terminal device even after the main program has
finished executing. By running the command in a
separate pseudo-terminal, this attack is no longer
possible.
A side effect of running the command in a new pseudo-
terminal is that input will be passed to the command
even if it is non-interactive. This means that, for
example, keys pressed while a non-interactive command
is running will be consumed by sudo instead of being
passed to the shell after the command exits.
This flag is on by default for sudo 1.9.14 and above.
user_command_timeouts
If set, the user may specify a timeout on the command
line. If the timeout expires before the command has
exited, the command will be terminated. If a timeout
is specified both in the sudoers file and on the
command line, the smaller of the two timeouts will be
used. See the Timeout_Spec section for a description
of the timeout syntax. This flag is off by default.
This setting is only supported by version 1.8.20 or
higher.
utmp_runas If set, sudo will store the name of the runas user when
updating the utmp (or utmpx) file. By default, sudo
stores the name of the invoking user. This flag is off
by default.
visiblepw By default, sudo will refuse to run if the user must
enter a password but it is not possible to disable echo
on the terminal. If the visiblepw flag is set, sudo
will prompt for a password even when it would be
visible on the screen. This makes it possible to run
things like `ssh somehost sudo ls' since by default,
ssh(1) does not allocate a tty when running a command.
This flag is off by default.
Integers:
closefrom Before it executes a command, sudo will close all open
file descriptors other than standard input, standard
output, and standard error (file descriptors 0-2). The
closefrom option can be used to specify a different
file descriptor at which to start closing. The default
is 3.
command_timeout The maximum amount of time a command is allowed to run
before it is terminated. See the Timeout_Spec section
for a description of the timeout syntax.
This setting is only supported by version 1.8.20 or
higher.
log_server_timeout
The maximum amount of time to wait when connecting to a
log server or waiting for a server response. See the
Timeout_Spec section for a description of the timeout
syntax. The default value is 30 seconds.
This setting is only supported by version 1.9.0 or
higher.
maxseq The maximum sequence number that will be substituted
for the `%{seq}' escape in the I/O log file (see the
iolog_dir description below for more information).
While the value substituted for `%{seq}' is in base 36,
maxseq itself should be expressed in decimal. Values
larger than 2176782336 (which corresponds to the base
36 sequence number "ZZZZZZ") will be silently truncated
to 2176782336. The default value is 2176782336.
Once the local sequence number reaches the value of
maxseq, it will "roll over" to zero, after which
sudoers will truncate and reuse any existing I/O log
path names.
This setting is only supported by version 1.8.7 or
higher.
passwd_tries The number of tries a user gets to enter his/her
password before sudo logs the failure and exits. The
default is 3.
syslog_maxlen On many systems, syslog(3) has a relatively small log
buffer. IETF RFC 5424 states that syslog servers must
support messages of at least 480 bytes and should
support messages up to 2048 bytes. By default, sudoers
creates log messages up to 980 bytes which corresponds
to the historic BSD syslog implementation which used a
1024 byte buffer to store the message, date, hostname,
and program name. To prevent syslog messages from
being truncated, sudoers will split up log messages
that are larger than syslog_maxlen bytes. When a
message is split, additional parts will include the
string "(command continued)" after the user name and
before the continued command line arguments.
This setting is only supported by version 1.8.19 or
higher.
Integers that can be used in a boolean context:
loglinelen Number of characters per line for the file log. This
value is used to decide when to wrap lines for nicer
log files. This has no effect on the syslog log file,
only the file log. The default is 80 (use 0 or negate
the option to disable word wrap).
passwd_timeout Number of minutes before the sudo password prompt times
out, or 0 for no timeout. The timeout may include a
fractional component if minute granularity is
insufficient, for example 2.5. The default is 0.
timestamp_timeout
Number of minutes that can elapse before sudo will ask
for a password again. The timeout may include a
fractional component if minute granularity is
insufficient, for example 2.5. The default is 5. Set
this to 0 to always prompt for a password. If set to a
value less than 0 the user's time stamp will not expire
until the system is rebooted. This can be used to
allow users to create or delete their own time stamps
via `sudo -v' and `sudo -k' respectively.
umask File mode creation mask to use when running the
command. Negate this option or set it to 0777 to
prevent sudoers from changing the umask. Unless the
umask_override flag is set, the actual umask will be
the union of the user's umask and the value of the
umask setting, which defaults to 0022. This guarantees
that sudo never lowers the umask when running a
command.
If umask is explicitly set in sudoers, it will override
any umask setting in PAM or login.conf. If umask is
not set in sudoers, the umask specified by PAM or
login.conf will take precedence. The umask setting in
PAM is not used for sudoedit, which does not create a
new PAM session.
Strings:
cmddenial_message
It set, sudo will display this message when a user is
denied access to run the specified command, but is
listed in the sudoers file for the host. This can be
used to provide additional, site-specific information
to the user when a command is denied by the security
policy. It does not override the standard warning the
user receives when a command is denied.
authfail_message Message that is displayed after a user fails to
authenticate. The message may include the `%d' escape
which will expand to the number of failed password
attempts. If set, it overrides the default message,
"%d incorrect password attempt(s)".
badpass_message Message that is displayed if a user enters an incorrect
password. The default is "Sorry, try again." unless
insults are enabled.
editor A colon (`:') separated list of editor path names used
by sudoedit and visudo. For sudoedit, this list is
used to find an editor when none of the SUDO_EDITOR,
VISUAL or EDITOR environment variables are set to an
editor that exists and is executable. For visudo, it
is used as a white list of allowed editors; visudo will
choose the editor that matches the user's SUDO_EDITOR,
VISUAL or EDITOR environment variable if possible, or
the first editor in the list that exists and is
executable if not. Unless invoked as sudoedit, sudo
does not preserve the SUDO_EDITOR, VISUAL or EDITOR
environment variables unless they are present in the
env_keep list or the env_reset option is disabled. The
default is /usr/bin/vi.
intercept_type The underlying mechanism used by the intercept and
log_subcmds options. It has the following possible
values:
dso Preload a dynamic shared object (shared
library) that intercepts the execve(2),
execl(3), execle(3), execlp(3), execv(3),
execvp(3), execvpe(3), and system(3) library
functions. A value of dso is incompatible with
sudo's SELinux RBAC support.
trace Use ptrace(2) to intercept the execve(2) system
call. This is only supported on Linux systems
where seccomp(2) filtering is enabled. If the
/proc/sys/kernel/seccomp/actions_avail file is
missing or does not contain a "trap" element,
setting intercept_type to trace will have no
effect and dso will be used instead.
The default is to use trace if it is supported by the
system and dso if it is not.
iolog_dir The top-level directory to use when constructing the
path name for the input/output log directory. Only
used if the log_input or log_output options are enabled
or when the LOG_INPUT or LOG_OUTPUT tags are present
for a command. The session sequence number, if any, is
stored in the directory. The default is
/var/log/sudo-io.
The following percent (`%') escape sequences are
supported:
%{seq}
expanded to a monotonically increasing base-36
sequence number, such as 0100A5, where every two
digits are used to form a new directory, e.g.,
01/00/A5
%{user}
expanded to the invoking user's login name
%{group}
expanded to the name of the invoking user's real
group-ID
%{runas_user}
expanded to the login name of the user the
command will be run as (e.g., root)
%{runas_group}
expanded to the group name of the user the
command will be run as (e.g., wheel)
%{hostname}
expanded to the local host name without the
domain name
%{command}
expanded to the base name of the command being
run
In addition, any escape sequences supported by the
system's strftime(3) function will be expanded.
To include a literal `%' character, the string `%%'
should be used.
Any path name separator characters (`/') present in the
user, group or host name will be replaced with an
underbar (`_') during expansion.
iolog_file The path name, relative to iolog_dir, in which to store
input/output logs when the log_input or log_output
options are enabled or when the LOG_INPUT or LOG_OUTPUT
tags are present for a command. iolog_file may contain
directory components. The default is `%{seq}'.
See the iolog_dir option above for a list of supported
percent (`%') escape sequences.
In addition to the escape sequences, path names that
end in six or more Xs will have the Xs replaced with a
unique combination of digits and letters, similar to
the mktemp(3) function.
If the path created by concatenating iolog_dir and
iolog_file already exists, the existing I/O log file
will be truncated and overwritten unless iolog_file
ends in six or more Xs.
iolog_flush If set, sudo will flush I/O log data to disk after each
write instead of buffering it. This makes it possible
to view the logs in real-time as the program is
executing but may significantly reduce the
effectiveness of I/O log compression. This flag is off
by default.
This setting is only supported by version 1.8.20 or
higher.
iolog_group The group name to look up when setting the group-ID on
new I/O log files and directories. If iolog_group is
not set, the primary group-ID of the user specified by
iolog_user is used. If neither iolog_group nor
iolog_user are set, I/O log files and directories are
created with group-ID 0.
This setting is only supported by version 1.8.19 or
higher.
iolog_mode The file mode to use when creating I/O log files. Mode
bits for read and write permissions for owner, group,
or other are honored, everything else is ignored. The
file permissions will always include the owner read and
write bits, even if they are not present in the
specified mode. When creating I/O log directories,
search (execute) bits are added to match the read and
write bits specified by iolog_mode. Defaults to 0600
(read and write by user only).
This setting is only supported by version 1.8.19 or
higher.
iolog_user The user name to look up when setting the user and
group-IDs on new I/O log files and directories. If
iolog_group is set, it will be used instead of the
user's primary group-ID. By default, I/O log files and
directories are created with user and group-ID 0.
This setting can be useful when the I/O logs are stored
on a Network File System (NFS) share. Having a
dedicated user own the I/O log files means that sudoers
does not write to the log files as user-ID 0, which is
usually not permitted by NFS.
This setting is only supported by version 1.8.19 or
higher.
lecture_status_dir
The directory in which sudo stores per-user lecture
status files. Once a user has received the lecture, a
zero-length file is created in this directory so that
sudo will not lecture the user again. This directory
should not be cleared when the system reboots. The
default is /var/db/sudo/lectured.
log_server_cabundle
The path to a certificate authority bundle file, in PEM
format, to use instead of the system's default
certificate authority database when authenticating the
log server. The default is to use the system's default
certificate authority database. This setting has no
effect unless log_servers is set and the remote log
server is secured with TLS.
This setting is only supported by version 1.9.0 or
higher.
log_server_peer_cert
The path to the sudo client's certificate file, in PEM
format. This setting is required when the remote log
server is secured with TLS and client certificate
validation is enabled. For sudo_logsrvd, client
certificate validation is controlled by the
tls_checkpeer option, which defaults to false.
This setting is only supported by version 1.9.0 or
higher.
log_server_peer_key
The path to the sudo client's private key file, in PEM
format. This setting is required when the remote log
server is secured with TLS and client certificate
validation is enabled. For sudo_logsrvd, client
certificate validation is controlled by the
tls_checkpeer flag, which defaults to false.
This setting is only supported by version 1.9.0 or
higher.
mailsub Subject of the mail sent to the mailto user. The
escape `%h' will expand to the host name of the
machine. Default is "*** SECURITY information for %h
***".
noexec_file As of sudo version 1.8.1 this option is no longer
supported. The path to the noexec file should now be
set in the sudo.conf(5) file.
pam_askpass_service
On systems that use PAM for authentication, this is the
service name used when the -A option is specified. The
default value is either `sudo' or `sudo', depending on
whether or not the -i option is also specified. See
the description of pam_service for more information.
This setting is only supported by version 1.9.9 or
higher.
pam_login_service
On systems that use PAM for authentication, this is the
service name used when the -i option is specified. The
default value is `sudo'. See the description of
pam_service for more information.
This setting is only supported by version 1.8.8 or
higher.
pam_service On systems that use PAM for authentication, the service
name specifies the PAM policy to apply. This usually
corresponds to an entry in the pam.conf file or a file
in the /etc/pam.d directory. The default value is
`sudo'.
This setting is only supported by version 1.8.8 or
higher.
passprompt The default prompt to use when asking for a password;
can be overridden via the -p option or the SUDO_PROMPT
environment variable. The following percent (`%')
escape sequences are supported:
%H expanded to the local host name including the
domain name (only if the machine's host name is
fully qualified or the fqdn option is set)
%h expanded to the local host name without the
domain name
%p expanded to the user whose password is being
asked for (respects the rootpw, targetpw and
runaspw flags in sudoers)
%U expanded to the login name of the user the
command will be run as (defaults to root)
%u expanded to the invoking user's login name
%% two consecutive `%' characters are collapsed into
a single `%' character
On systems that use PAM for authentication, passprompt
will only be used if the prompt provided by the PAM
module matches the string "Password: " or "username's
Password: ". This ensures that the passprompt setting
does not interfere with challenge-response style
authentication. The passprompt_override flag can be
used to change this behavior.
The default value is `Password: '.
runas_default The default user to run commands as if the -u option is
not specified on the command line. This defaults to
root.
sudoers_locale Locale to use when parsing the sudoers file, logging
commands, and sending email. Changing the locale may
affect how sudoers is interpreted. Defaults to `C'.
timestamp_type sudoers uses per-user time stamp files for credential
caching. The timestamp_type option can be used to
specify the type of time stamp record used. It has the
following possible values:
global A single time stamp record is used for all of a
user's login sessions, regardless of the
terminal or parent process ID. An additional
record is used to serialize password prompts
when sudo is used multiple times in a pipeline,
but this does not affect authentication.
ppid A single time stamp record is used for all
processes with the same parent process ID
(usually the shell). Commands run from the
same shell (or other common parent process)
will not require a password for
timestamp_timeout minutes (5 by default).
Commands run via sudo with a different parent
process ID, for example from a shell script,
will be authenticated separately.
tty One time stamp record is used for each
terminal, which means that a user's login
sessions are authenticated separately. If no
terminal is present, the behavior is the same
as ppid. Commands run from the same terminal
will not require a password for
timestamp_timeout minutes (5 by default).
kernel The time stamp is stored in the kernel as an
attribute of the terminal device. If no
terminal is present, the behavior is the same
as ppid. Negative timestamp_timeout values are
not supported and positive values are limited
to a maximum of 60 minutes. This is currently
only supported on OpenBSD.
The default value is tty.
This setting is only supported by version 1.8.21 or
higher.
timestampdir The directory in which sudo stores its time stamp
files. This directory should be cleared when the
system reboots. The default is
/opt/local/var/run/sudo/ts.
timestampowner The owner of the lecture status directory, time stamp
directory and all files stored therein. The default is
root.
Strings that can be used in a boolean context:
admin_flag The admin_flag option specifies the path to a file that is
created the first time a user that is a member of the sudo
or admin groups runs sudo. Only available if sudo is
configured with the --enable-admin-flag option. The
default value is ~/.sudo_as_admin_successful.
env_file The env_file option specifies the fully qualified path to a
file containing variables to be set in the environment of
the program being run. Entries in this file should either
be of the form `VARIABLE=value' or `export VARIABLE=value'.
The value may optionally be enclosed in single or double
quotes. Variables in this file are only added if the
variable does not already exist in the environment. This
file is considered to be part of the security policy, its
contents are not subject to other sudo environment
restrictions such as env_keep and env_check.
exempt_group Users in this group are exempt from password and PATH
requirements. The group name specified should not include
a `%' prefix. This is not set by default.
fdexec Determines whether sudo will execute a command by its path
or by an open file descriptor. It has the following
possible values:
always Always execute by file descriptor.
never Never execute by file descriptor.
digest_only
Only execute by file descriptor if the command has
an associated digest in the sudoers file.
The default value is digest_only. This avoids a time of
check versus time of use race condition when the command is
located in a directory writable by the invoking user.
fdexec will change the first element of the argument vector
for scripts ($0 in the shell) due to the way the kernel
runs script interpreters. Instead of being a normal path,
it will refer to a file descriptor. For example, /dev/fd/4
on Solaris and /proc/self/fd/4 on Linux. A workaround is
to use the SUDO_COMMAND environment variable instead.
The fdexec setting is only used when the command is matched
by path name. It has no effect if the command is matched
by the built-in ALL alias.
This setting is only supported by version 1.8.20 or higher.
If the operating system does not support the fexecve(2)
system call, this setting has no effect.
group_plugin A string containing a sudoers group plugin with optional
arguments. The string should consist of the plugin path,
either fully-qualified or relative to the
/opt/local/libexec/sudo directory, followed by any
configuration arguments the plugin requires. These
arguments (if any) will be passed to the plugin's
initialization function. If arguments are present, the
string must be enclosed in double quotes ("").
On 64-bit systems, if the plugin is present but cannot be
loaded, sudoers will look for a 64-bit version and, if it
exists, load that as a fallback. The exact rules for this
vary by system. On Solaris, if the plugin is stored in a
directory ending in "lib", sudoers will create a fallback
path by appending "/64" to the directory name;
/opt/local/lib/group_plugin.so becomes
/opt/local/lib/64/group_plugin.so. On Linux, a directory
ending in "lib" will be transformed to "lib64" as the
fallback path; /opt/local/lib/group_plugin.so becomes
/opt/local/lib64/group_plugin.so. On all other systems,
the fallback path is generated by adding a "64" before the
file extension; group_plugin.so becomes group_plugin64.so.
On AIX systems, the plugin may be either a shared object
ending in `.so' or an archive file containing a shared
object ending in `.a' with the name of the shared object in
parentheses at the end.
For more information see GROUP PROVIDER PLUGINS.
lecture This option controls when a short lecture will be printed
along with the password prompt. It has the following
possible values:
always Always lecture the user.
never Never lecture the user.
once Only lecture the user the first time they run sudo.
If no value is specified, a value of once is implied.
Negating the option results in a value of never being used.
The default value is once.
lecture_file Path to a file containing an alternate sudo lecture that
will be used in place of the standard lecture if the named
file exists. By default, sudo uses a built-in lecture.
listpw This option controls when a password will be required when
a user runs sudo with the -l option. It has the following
possible values:
all All the user's sudoers file entries for the current
host must have the NOPASSWD flag set to avoid
entering a password.
always
The user must always enter a password to use the -l
option.
any At least one of the user's sudoers file entries for
the current host must have the NOPASSWD flag set to
avoid entering a password.
never
The user need never enter a password to use the -l
option.
If no value is specified, a value of any is implied.
Negating the option results in a value of never being used.
The default value is any.
log_format The event log format. Supported log formats are:
json Currently, this is an alias for json_pretty. In a
future version of sudo, json will be equivalent to
json_compact. JSON log entries contain the full user
details as well as the execution environment if the
command was allowed.
json_compact
Log events in "compact" (minified) JSON format. Each
event is written as a separate JSON object on single
line without extraneous white space. Due to
limitations of the protocol, JSON events sent via
syslog may be truncated.
json_pretty
Log events in "pretty" JSON format. When logging to
a file, the entire file is treated as a single JSON
object consisting of multiple events, each event
spanning multiple lines. When logging via syslog,
there is no difference between the json_pretty and
json_compact formats.
sudo Log events in traditional sudo-style format, see
EVENT LOGGING for details.
This setting affects logs sent via syslog(3) as well as the
file specified by the logfile setting, if any. The default
value is sudo.
logfile Path to the sudo log file (not the syslog log file).
Setting a path turns on logging to a file; negating this
option turns it off. By default, sudo logs via syslog.
mailerflags Flags to use when invoking mailer. Defaults to -t.
mailerpath Path to mail program used to send warning mail (negate to
prevent sudo from sending mail). Defaults to the path to
sendmail found at configure time.
mailfrom Address to use for the "from" address when sending warning
and error mail. The address should be enclosed in double
quotes ("") to protect against sudo interpreting the `@'
sign. Defaults to the name of the user running sudo.
mailto Address to send warning and error mail to (negate to
prevent sudo from sending mail). The address should be
enclosed in double quotes ("") to protect against sudo
interpreting the `@' sign. Defaults to root.
rlimit_as The maximum size to which the process's address space may
grow (in bytes), if supported by the operating system. See
Resource limits for more information.
rlimit_core The largest size core dump file that may be created (in
bytes). See Resource limits for more information.
Defaults to 0 (no core dump created).
rlimit_cpu The maximum amount of CPU time that the process may use (in
seconds). See Resource limits for more information.
rlimit_data The maximum size of the data segment for the process (in
bytes). See Resource limits for more information.
rlimit_fsize The largest size file that the process may create (in
bytes). See Resource limits for more information.
rlimit_locks The maximum number of locks that the process may establish,
if supported by the operating system. See Resource limits
for more information.
rlimit_memlock
The maximum size that the process may lock in memory (in
bytes), if supported by the operating system. See Resource
limits for more information.
rlimit_nofile
The maximum number of files that the process may have open.
See Resource limits for more information.
rlimit_nproc The maximum number of processes that the user may run
simultaneously. See Resource limits for more information.
rlimit_rss The maximum size to which the process's resident set size
may grow (in bytes). See Resource limits for more
information.
rlimit_stack The maximum size to which the process's stack may grow (in
bytes). See Resource limits for more information.
restricted_env_file
The restricted_env_file option specifies the fully
qualified path to a file containing variables to be set in
the environment of the program being run. Entries in this
file should either be of the form `VARIABLE=value' or
`export VARIABLE=value'. The value may optionally be
enclosed in single or double quotes. Variables in this
file are only added if the variable does not already exist
in the environment. Unlike env_file, the file's contents
are not trusted and are processed in a manner similar to
that of the invoking user's environment. If env_reset is
enabled, variables in the file will only be added if they
are matched by either the env_check or env_keep list. If
env_reset is disabled, variables in the file are added as
long as they are not matched by the env_delete list. In
either case, the contents of restricted_env_file are
processed before the contents of env_file.
runchroot If set, sudo will use this value for the root directory
when running a command. The special value "*" will allow
the user to specify the root directory via sudo's -R
option. See the Chroot_Spec section for more details.
It is only possible to use runchroot as a command-specific
Defaults setting if the command exists with the same path
both inside and outside the chroot jail. This restriction
does not apply to global, host, or user-based Defaults
settings or to a Cmnd_Spec that includes a Chroot_Spec.
This setting is only supported by version 1.9.3 or higher.
runcwd If set, sudo will use this value for the working directory
when running a command. The special value "*" will allow
the user to specify the working directory via sudo's -D
option. See the Chdir_Spec section for more details.
This setting is only supported by version 1.9.3 or higher.
secure_path If set, sudo will use this value in place of the user's
PATH environment variable. There are two basic use cases
for secure_path:
1. To make it possible for sudo to find system
administrator commands located in directories that may
not be in the default user path, such as /usr/sbin.
2. To help protect scripts and programs that execute other
commands without first setting PATH to a safe value.
Otherwise, a user with limited privileges may be able to
run arbitrary commands by manipulating the PATH if the
command being run executes other commands without using
a fully-qualified path name.
Users in the group specified by the exempt_group option are
not affected by secure_path. This option is disabled by
default.
syslog Syslog facility if syslog is being used for logging (negate
to disable syslog logging). Defaults to authpriv.
The following syslog facilities are supported: authpriv (if
your OS supports it), auth, daemon, user, local0, local1,
local2, local3, local4, local5, local6, and local7.
syslog_badpri
Syslog priority to use when the user is not allowed to run
a command or when authentication is unsuccessful. Defaults
to alert.
The following syslog priorities are supported: alert, crit,
debug, emerg, err, info, notice, warning, and none.
Negating the option or setting it to a value of none will
disable logging of unsuccessful commands.
syslog_goodpri
Syslog priority to use when the user is allowed to run a
command and authentication is successful. Defaults to
notice.
See syslog_badpri for the list of supported syslog
priorities. Negating the option or setting it to a value
of none will disable logging of successful commands.
verifypw This option controls when a password will be required when
a user runs sudo with the -v option. It has the following
possible values:
all All the user's sudoers file entries for the current
host must have the NOPASSWD flag set to avoid
entering a password.
always The user must always enter a password to use the -v
option.
any At least one of the user's sudoers file entries for
the current host must have the NOPASSWD flag set to
avoid entering a password.
never The user need never enter a password to use the -v
option.
If no value is specified, a value of all is implied.
Negating the option results in a value of never being used.
The default value is all.
Lists that can be used in a boolean context:
env_check Environment variables to be removed from the user's
environment unless they are considered "safe". For all
variables except TZ, "safe" means that the variable's
value does not contain any `%' or `/' characters. This
can be used to guard against printf-style format
vulnerabilities in poorly-written programs. The TZ
variable is considered unsafe if any of the following
are true:
o It consists of a fully-qualified path name,
optionally prefixed with a colon (`:'), that does
not match the location of the zoneinfo directory.
o It contains a .. path element.
o It contains white space or non-printable characters.
o It is longer than the value of PATH_MAX.
The argument may be a double-quoted, space-separated
list or a single value without double-quotes. The list
can be replaced, added to, deleted from, or disabled by
using the `=', `+=', `-=', and `!' operators
respectively. Regardless of whether the env_reset
option is enabled or disabled, variables specified by
env_check will be preserved in the environment if they
pass the aforementioned check. The global list of
environment variables to check is displayed when sudo
is run by root with the -V option.
env_delete Environment variables to be removed from the user's
environment when the env_reset option is not in effect.
The argument may be a double-quoted, space-separated
list or a single value without double-quotes. The list
can be replaced, added to, deleted from, or disabled by
using the `=', `+=', `-=', and `!' operators
respectively. The global list of environment variables
to remove is displayed when sudo is run by root with
the -V option. Many operating systems will remove
potentially dangerous variables from the environment of
any set-user-ID process (such as sudo).
env_keep Environment variables to be preserved in the user's
environment when the env_reset option is in effect.
This allows fine-grained control over the environment
sudo-spawned processes will receive. The argument may
be a double-quoted, space-separated list or a single
value without double-quotes. The list can be replaced,
added to, deleted from, or disabled by using the `=',
`+=', `-=', and `!' operators respectively. The global
list of variables to keep is displayed when sudo is run
by root with the -V option.
Preserving the HOME environment variable has security
implications since many programs use it when searching
for configuration or data files. Adding HOME to
env_keep may enable a user to run unrestricted commands
via sudo and is strongly discouraged. Users wishing to
edit files with sudo should run sudoedit (or sudo -e)
to get their accustomed editor configuration instead of
invoking the editor directly.
log_servers A list of one or more servers to use for remote event
and I/O log storage, separated by white space. Log
servers must be running sudo_logsrvd or another service
that implements the protocol described by
sudo_logsrv.proto(5).
Server addresses should be of the form
"host[:port][(tls)]". The host portion may be a host
name, an IPv4 address, or an IPv6 address in square
brackets.
If the optional tls flag is present, the connection
will be secured with Transport Layer Security (TLS)
version 1.2 or 1.3. Versions of TLS prior to 1.2 are
not supported.
If a port is specified, it may either be a port number
or a well-known service name as defined by the system
service name database. If no port is specified, port
30343 will be used for plaintext connections and port
30344 will be used for TLS connections.
When log_servers is set, event log data will be logged
both locally (see the syslog and log_file settings) as
well as remotely, but I/O log data will only be logged
remotely. If multiple hosts are specified, they will
be attempted in reverse order. If no log servers are
available, the user will not be able to run a command
unless either the ignore_iolog_errors flag (I/O logging
enabled) or the ignore_log_errors flag (I/O logging
disabled) is set. Likewise, if the connection to the
log server is interrupted while sudo is running, the
command will be terminated unless the
ignore_iolog_errors flag (I/O logging enabled) or the
ignore_log_errors flag (I/O logging disabled) is set.
This setting is only supported by version 1.9.0 or
higher.
passprompt_regex A list of POSIX extended regular expressions used to
match password prompts in the terminal output. As an
extension, if the regular expression begins with
"(?i)", it will be matched in a case-insensitive
manner. Each regular expression is limited to 1024
characters. This option is only used when
log_passwords has been disabled. The default value is
"[Pp]assword[: ]*"
This setting is only supported by version 1.9.10 or
higher.
GROUP PROVIDER PLUGINS
The sudoers plugin supports its own plugin interface to allow non-Unix
group lookups which can query a group source other than the standard Unix
group database. This can be used to implement support for the
nonunix_group syntax described earlier.
Group provider plugins are specified via the group_plugin setting. The
argument to group_plugin should consist of the plugin path, either fully-
qualified or relative to the /opt/local/libexec/sudo directory, followed
by any configuration options the plugin requires. These options (if
specified) will be passed to the plugin's initialization function. If
options are present, the string must be enclosed in double quotes ("").
The following group provider plugins are installed by default:
group_file
The group_file plugin supports an alternate group file that uses
the same syntax as the /etc/group file. The path to the group file
should be specified as an option to the plugin. For example, if
the group file to be used is /etc/sudo-group:
Defaults group_plugin="group_file.so /etc/sudo-group"
system_group
The system_group plugin supports group lookups via the standard C
library functions getgrnam(3) and getgrid(3). This plugin can be
used in instances where the user belongs to groups not present in
the user's supplemental group vector. This plugin takes no
options:
Defaults group_plugin=system_group.so
The group provider plugin API is described in detail in sudo_plugin(5).
EVENT LOGGING
sudoers can log events in either JSON or sudo format, this section
describes the sudo log format. Depending on sudoers configuration,
sudoers can log events via syslog(3), to a local log file, or both. The
log format is almost identical in both cases. Any control characters
present in the log data are formatted in octal with a leading `#'
character. For example, a horizontal tab is stored as `#011' and an
embedded carriage return is stored as `#015'. In addition, space
characters in the command path are stored as `#040'. Command line
arguments that contain spaces are enclosed in single quotes (''). This
makes it possible to distinguish multiple command line arguments from a
single argument that contains spaces. Literal single quotes and
backslash characters (`\') in command line arguments are escaped with a
backslash.
Accepted command log entries
Commands that sudo runs are logged using the following format (split into
multiple lines for readability):
date hostname progname: username : TTY=ttyname ; CHROOT=chroot ; \
PWD=cwd ; USER=runasuser ; GROUP=runasgroup ; TSID=logid ; \
ENV=env_vars COMMAND=command
Where the fields are as follows:
date The date the command was run. Typically, this is in the
format "MMM, DD, HH:MM:SS". If logging via syslog(3), the
actual date format is controlled by the syslog daemon. If
logging to a file and the log_year option is enabled, the
date will also include the year.
hostname The name of the host sudo was run on. This field is only
present when logging via syslog(3).
progname The name of the program, usually sudo or sudoedit. This
field is only present when logging via syslog(3).
username The login name of the user who ran sudo.
ttyname The short name of the terminal (e.g., "console", "tty01",
or "pts/0") sudo was run on, or "unknown" if there was no
terminal present.
chroot The root directory that the command was run in, if one was
specified.
cwd The current working directory that sudo was run in.
runasuser The user the command was run as.
runasgroup The group the command was run as if one was specified on
the command line.
logid An I/O log identifier that can be used to replay the
command's output. This is only present when the log_input
or log_output option is enabled.
env_vars A list of environment variables specified on the command
line, if specified.
command The actual command that was executed, including any command
line arguments.
Messages are logged using the locale specified by sudoers_locale, which
defaults to the `C' locale.
Denied command log entries
If the user is not allowed to run the command, the reason for the denial
will follow the user name. Possible reasons include:
user NOT in sudoers
The user is not listed in the sudoers file.
user NOT authorized on host
The user is listed in the sudoers file but is not allowed to run
commands on the host.
command not allowed
The user is listed in the sudoers file for the host but they are not
allowed to run the specified command.
3 incorrect password attempts
The user failed to enter their password after 3 tries. The actual
number of tries will vary based on the number of failed attempts and
the value of the passwd_tries option.
a password is required
The -n option was specified but a password was required.
sorry, you are not allowed to set the following environment variables
The user specified environment variables on the command line that were
not allowed by sudoers.
Error log entries
If an error occurs, sudoers will log a message and, in most cases, send a
message to the administrator via email. Possible errors include:
parse error in /opt/local/etc/sudoers near line N
sudoers encountered an error when parsing the specified file. In some
cases, the actual error may be one line above or below the line number
listed, depending on the type of error.
problem with defaults entries
The sudoers file contains one or more unknown Defaults settings. This
does not prevent sudo from running, but the sudoers file should be
checked using visudo.
timestamp owner (username): No such user
The time stamp directory owner, as specified by the timestampowner
setting, could not be found in the password database.
unable to open/read /opt/local/etc/sudoers
The sudoers file could not be opened for reading. This can happen
when the sudoers file is located on a remote file system that maps
user-ID 0 to a different value. Normally, sudoers tries to open the
sudoers file using group permissions to avoid this problem. Consider
either changing the ownership of /opt/local/etc/sudoers or adding an
argument like "sudoers_uid=N" (where `N' is the user-ID that owns the
sudoers file) to the end of the sudoers Plugin line in the
sudo.conf(5) file.
unable to open /opt/local/etc/sudoers
The /opt/local/etc/sudoers file is missing.
/opt/local/etc/sudoers is not a regular file
The /opt/local/etc/sudoers file exists but is not a regular file or
symbolic link.
/opt/local/etc/sudoers is owned by uid N, should be 0
The sudoers file has the wrong owner. If you wish to change the
sudoers file owner, add "sudoers_uid=N" (where `N' is the user-ID that
owns the sudoers file) to the sudoers Plugin line in the sudo.conf(5)
file.
/opt/local/etc/sudoers is world writable
The permissions on the sudoers file allow all users to write to it.
The sudoers file must not be world-writable, the default file mode is
0440 (readable by owner and group, writable by none). The default
mode may be changed via the "sudoers_mode" option to the sudoers
Plugin line in the sudo.conf(5) file.
/opt/local/etc/sudoers is owned by gid N, should be 1
The sudoers file has the wrong group ownership. If you wish to change
the sudoers file group ownership, add "sudoers_gid=N" (where `N' is
the group-ID that owns the sudoers file) to the sudoers Plugin line in
the sudo.conf(5) file.
unable to open /opt/local/var/run/sudo/ts/user-ID
sudoers was unable to read or create the user's time stamp file. This
can happen when timestampowner is set to a user other than root and
the mode on /opt/local/var/run/sudo is not searchable by group or
other. The default mode for /opt/local/var/run/sudo is 0711.
unable to write to /opt/local/var/run/sudo/ts/user-ID
sudoers was unable to write to the user's time stamp file.
/opt/local/var/run/sudo/ts is owned by uid X, should be Y
The time stamp directory is owned by a user other than timestampowner.
This can occur when the value of timestampowner has been changed.
sudoers will ignore the time stamp directory until the owner is
corrected.
/opt/local/var/run/sudo/ts is group writable
The time stamp directory is group-writable; it should be writable only
by timestampowner. The default mode for the time stamp directory is
0700. sudoers will ignore the time stamp directory until the mode is
corrected.
Notes on logging via syslog
By default, sudoers logs messages via syslog(3). The date, hostname, and
progname fields are added by the system's syslog(3) function, not sudoers
itself. As such, they may vary in format on different systems.
The maximum size of syslog messages varies from system to system. The
syslog_maxlen setting can be used to change the maximum syslog message
size from the default value of 980 bytes. For more information, see the
description of syslog_maxlen.
Notes on logging to a file
If the logfile option is set, sudoers will log to a local file, such as
/var/log/sudo. When logging to a file, sudoers uses a format similar to
syslog(3), with a few important differences:
1. The progname field is not present.
2. The hostname is only logged if the log_host option is enabled.
3. The date does not include the year unless the log_year option is
enabled.
4. Lines that are longer than loglinelen characters (80 by default) are
word-wrapped and continued on the next line with a four character
indent. This makes entries easier to read for a human being, but
makes it more difficult to use grep(1) on the log files. If the
loglinelen option is set to 0 (or negated with a `!'), word wrap
will be disabled.
I/O LOGGING
When I/O logging is enabled, sudo will runs the command in a pseudo-
terminal, logging user input and/or output, depending on which sudoers
flags are enabled. There are five distinct types of I/O that can be
logged, each with a corresponding sudoers flag.
Type Flag Description
terminal input log_ttyin keystrokes entered by the user
terminal output log_ttyout command output displayed to the screen
standard input log_stdin input from a pipe or a file
standard output log_stdout output to a pipe or a file
standard error log_stderr output to a pipe or a file
In addition to flags described the above, the log_input flag and
LOG_INPUT command tag set both log_ttyin and log_stdin. The log_output
flag and LOG_OUTPUT command tag set log_ttyout, log_stdout, and
log_stderr.
To capture terminal input and output, sudo run the command in a pseudo-
terminal, logging the input and output before passing it on to the user.
To capture the standard input, standard output or standard error, sudo
uses a pipe to interpose itself between the input or output stream,
logging the I/O before passing it to the other end of the pipe.
I/O can be logged either to the local machine or to a remote log server.
For local logs, I/O is logged to the directory specified by the iolog_dir
option (/var/log/sudo-io by default) using a unique session ID that is
included in the sudo log line, prefixed with `TSID='. The iolog_file
option may be used to control the format of the session ID. For remote
logs, the log_servers setting is used to specify one or more log servers
running sudo_logsrvd or another server that implements the protocol
described by sudo_logsrv.proto(5).
I/O logging pitfals
When logging standard input, anything sent to the standard input will be
consumed, regardless of whether or not the command run via sudo is
actively reading the standard input. This may have unexpected results
when using sudo in a shell script that expects to process the standard
input. For example, given the following shell script:
#!/bin/sh
sudo echo testing
echo done
It will behave as expected when the script is passed to the shell as a an
argument:
$ sh test.sh
testing
done
However, if the script is passed to the shell on the standard input, the
`sudo echo testing' command will consume the rest of the script. This
means that the `echo done' statement is never executed.
$ sh -s < test.sh
testing
There are several ways to work around this problem:
1. Redirect the standard input from /dev/null when running a command
via sudo that does not need to read the standard input.
sudo echo testing < /dev/null
2. Pass the script to the shell by path name instead of via the
standard input.
sh test.sh
3. Disable logging the standard input for commands that do not need to
read the standard input.
Defaults!/bin/echo !log_stdin
Depending on the command, it may not be desirable to log the standard
input or standard output. For example, I/O logging of commands that send
or receive large amount of data via the standard output or standard input
such as rsync(1) and tar(1) could fill up the log file system with
superfluous data. It is possible to disable logging of the standard
input and standard output for such commands as follows:
Cmnd_Alias COPY_CMDS = /usr/bin/tar, /usr/bin/cpio, /usr/bin/rsync
# Log input and output but omit stdin and stdout when copying files.
Defaults log_input, log_output
Defaults!COPY_CMDS !log_stdin, !log_stdout
However, be aware that using the log_input flag or the LOG_INPUT command
tag will also enable log_stdin. Likewise, the log_ouput flag or the
LOG_OUTPUT command tag will enable log_stdout and log_stderr. Careful
ordering of rules may be necessary to achieve the results that you
expect.
I/O log format
For both local and remote I/O logs, each log is stored in a separate
directory that contains the following files:
log A text file containing information about the command. The
first line consists of the following colon-delimited fields:
the time the command was run, the name of the user who ran
sudo, the name of the target user, the name of the target group
(optional), the terminal that sudo was run from, and the number
of lines and columns of the terminal. The second and third
lines contain the working directory the command was run from
and the path name of the command itself (with arguments if
present).
log.json A JSON-formatted file containing information about the command.
This is similar to the log file but contains additional
information and is easily extensible. The log.json file will
be used by sudoreplay(8) in preference to the log file if it
exists. The file may contain the following elements:
timestamp
A JSON object containing time the command was run. It
consists of two values, seconds and nanoseconds.
columns
The number of columns of the terminal the command ran on,
or zero if no terminal was present.
command
The fully-qualified path of the command that was run.
lines
The number of lines of the terminal the command ran on,
or zero if no terminal was present.
runargv
A JSON array representing the command's argument vector
as passed to the execve(2) system call.
runenv
A JSON array representing the command's environment as
passed to the execve(2) system call.
rungid
The group ID the command ran as. This element is only
present when the user specifies a group on the command
line.
rungroup
The name of the group the command ran as. This element
is only present when the user specifies a group on the
command line.
runuid
The user ID the command ran as.
runuser
The name of the user the command ran as.
submitcwd
The current working directory at the time sudo was run.
submithost
The name of the host the command was run on.
submituser
The name of the user who ran the command via sudo.
ttyname
The path name of the terminal the user invoked sudo from.
If the command was run in a pseudo-terminal, ttyname will
be different from the terminal the command actually ran
in.
timing Timing information used to replay the session. Each line
consists of the I/O log entry type and amount of time since the
last entry, followed by type-specific data. The I/O log entry
types and their corresponding type-specific data are:
0 standard input, number of bytes in the entry
1 standard output, number of bytes in the entry
2 standard error, number of bytes in the entry
3 terminal input, number of bytes in the entry
4 terminal output, number of bytes in the entry
5 window change, new number lines and columns
6 bug compatibility for sudo 1.8.7 terminal output
7 command suspend or resume, signal received
ttyin Raw input from the user's terminal, exactly as it was received.
This file is only present if the log_input or log_ttyin flags
are set and sudo was run from a terminal. No post-processing
is performed. For manual viewing, you may wish to convert
carriage return characters in the log to line feeds. For
example: `gunzip -c ttyin | tr "\r" "\n"'
stdin The standard input when no terminal is present, or input
redirected from a pipe or file. This file is only present if
the log_input or log_stdin flags are set and the standard input
is not connected to a terminal.
ttyout Output from the pseudo-terminal (what the command writes to the
screen). Terminal-specific post-processing is performed before
the data is logged. This means that, for example, line feeds
are usually converted to line feed/carriage return pairs and
tabs may be expanded to spaces. This file is only present if
the log_output or log_ttyout flags are set and sudo was run
from a terminal.
stdout The standard output when no terminal is present, or output
redirected to a pipe or file. This file is only present if the
log_output or log_stdout flags are set and the standard output
is not connected to a terminal.
stderr The standard error when no terminal is present, or output
redirected to a pipe or file. This file is only present if the
log_output or log_stderr flags are set and the standard error
is not connected to a terminal.
All files other than log are compressed in gzip format unless the
compress_io flag has been disabled. Due to buffering, it is not normally
possible to display the I/O logs in real-time as the program is
executing. The I/O log data will not be complete until the program run
by sudo has exited or has been terminated by a signal. The iolog_flush
flag can be used to disable buffering, in which case I/O log data is
written to disk as soon as it is available. The output portion of an I/O
log file can be viewed with the sudoreplay(8) utility, which can also be
used to list or search the available logs.
User input may contain sensitive information such as passwords (even if
they are not echoed to the screen), which will be stored in the log file
unencrypted. In most cases, logging the command output via log_output or
LOG_OUTPUT is all that is required. When logging input, consider
disabling the log_passwords flag.
Since each session's I/O logs are stored in a separate directory,
traditional log rotation utilities cannot be used to limit the number of
I/O logs. The simplest way to limit the number of I/O is by setting the
maxseq option to the maximum number of logs you wish to store. Once the
I/O log sequence number reaches maxseq, it will be reset to zero and
sudoers will truncate and reuse any existing I/O logs.
FILES
/opt/local/etc/sudo.conf Sudo front-end configuration
/opt/local/etc/sudoers List of who can run what
/etc/group Local groups file
/etc/netgroup List of network groups
/var/log/sudo-io I/O log files
/opt/local/var/run/sudo/ts
Directory containing time stamps for the
sudoers security policy
/var/db/sudo/lectured Directory containing lecture status files for
the sudoers security policy
/etc/environment Initial environment for -i mode on AIX and
Linux systems
EXAMPLES
Below are example sudoers file entries. Admittedly, some of these are a
bit contrived. First, we allow a few environment variables to pass and
then define our aliases:
# Run X applications through sudo; HOME is used to find the
# .Xauthority file. Other programs use HOME to locate configuration
# files and this may lead to privilege escalation!
Defaults env_keep += "DISPLAY HOME"
# User alias specification
User_Alias FULLTIMERS = millert, mikef, dowdy
User_Alias PARTTIMERS = bostley, jwfox, crawl
User_Alias WEBADMIN = will, wendy, wim
# Runas alias specification
Runas_Alias OP = root, operator
Runas_Alias DB = oracle, sybase
Runas_Alias ADMINGRP = adm, oper
# Host alias specification
Host_Alias SPARC = bigtime, eclipse, moet, anchor :\
SGI = grolsch, dandelion, black :\
ALPHA = widget, thalamus, foobar :\
HPPA = boa, nag, python
Host_Alias CUNETS = 128.138.0.0/255.255.0.0
Host_Alias CSNETS = 128.138.243.0, 128.138.204.0/24, 128.138.242.0
Host_Alias SERVERS = primary, mail, www, ns
Host_Alias CDROM = orion, perseus, hercules
# Cmnd alias specification
Cmnd_Alias DUMPS = /usr/bin/mt, /usr/sbin/dump, /usr/sbin/rdump,\
/usr/sbin/restore, /usr/sbin/rrestore,\
sha224:0GomF8mNN3wlDt1HD9XldjJ3SNgpFdbjO1+NsQ== \
/home/operator/bin/start_backups
Cmnd_Alias KILL = /usr/bin/kill
Cmnd_Alias PRINTING = /usr/sbin/lpc, /usr/bin/lprm
Cmnd_Alias SHUTDOWN = /usr/sbin/shutdown
Cmnd_Alias HALT = /usr/sbin/halt
Cmnd_Alias REBOOT = /usr/sbin/reboot
Cmnd_Alias SHELLS = /usr/bin/sh, /usr/bin/csh, /usr/bin/ksh,\
/usr/local/bin/tcsh, /usr/bin/rsh,\
/usr/local/bin/zsh
Cmnd_Alias SU = /usr/bin/su
Cmnd_Alias PAGERS = /usr/bin/more, /usr/bin/pg, /usr/bin/less
Here we override some of the compiled in default values. We want sudo to
log via syslog(3) using the auth facility in all cases and for commands
to be run with the target user's home directory as the working directory.
We don't want to subject the full time staff to the sudo lecture and we
want to allow them to run commands in a chroot(2) "sandbox" via the -R
option. User millert need not provide a password and we don't want to
reset the LOGNAME or USER environment variables when running commands as
root. Additionally, on the machines in the SERVERS Host_Alias, we keep
an additional local log file and make sure we log the year in each log
line since the log entries will be kept around for several years.
Lastly, we disable shell escapes for the commands in the PAGERS
Cmnd_Alias (/usr/bin/more, /usr/bin/pg and /usr/bin/less). This will not
effectively constrain users with sudo ALL privileges.
# Override built-in defaults
Defaults syslog=auth,runcwd=~
Defaults>root !set_logname
Defaults:FULLTIMERS !lecture,runchroot=*
Defaults:millert !authenticate
Defaults@SERVERS log_year, logfile=/var/log/sudo.log
Defaults!PAGERS noexec
The User specification is the part that actually determines who may run
what.
root ALL = (ALL) ALL
%wheel ALL = (ALL) ALL
We let root and any user in group wheel run any command on any host as
any user.
FULLTIMERS ALL = NOPASSWD: ALL
Full time sysadmins (millert, mikef, and dowdy) may run any command on
any host without authenticating themselves.
PARTTIMERS ALL = ALL
Part time sysadmins bostley, jwfox, and crawl) may run any command on any
host but they must authenticate themselves first (since the entry lacks
the NOPASSWD tag).
jack CSNETS = ALL
The user jack may run any command on the machines in the CSNETS alias
(the networks 128.138.243.0, 128.138.204.0, and 128.138.242.0). Of those
networks, only 128.138.204.0 has an explicit netmask (in CIDR notation)
indicating it is a class C network. For the other networks in CSNETS,
the local machine's netmask will be used during matching.
lisa CUNETS = ALL
The user lisa may run any command on any host in the CUNETS alias (the
class B network 128.138.0.0).
operator ALL = DUMPS, KILL, SHUTDOWN, HALT, REBOOT, PRINTING,\
sudoedit /etc/printcap, /usr/oper/bin/
The operator user may run commands limited to simple maintenance. Here,
those are commands related to backups, killing processes, the printing
system, shutting down the system, and any commands in the directory
/usr/oper/bin/. One command in the DUMPS Cmnd_Alias includes a sha224
digest, /home/operator/bin/start_backups. This is because the directory
containing the script is writable by the operator user. If the script is
modified (resulting in a digest mismatch) it will no longer be possible
to run it via sudo.
joe ALL = /usr/bin/su operator
The user joe may only su(1) to operator.
pete HPPA = /usr/bin/passwd [A-Za-z]*, !/usr/bin/passwd *root*
%opers ALL = (: ADMINGRP) /usr/sbin/
Users in the opers group may run commands in /usr/sbin/ as themselves
with any group in the ADMINGRP Runas_Alias (the adm and oper groups).
The user pete is allowed to change anyone's password except for root on
the HPPA machines. Because command line arguments are matched as a
single, concatenated string, the `*' wildcard will match multiple words.
This example assumes that passwd(1) does not take multiple user names on
the command line. On systems with GNU getopt(3), options to passwd(1)
may be specified after the user argument. As a result, this rule will
also allow:
passwd username --expire
which may not be desirable.
bob SPARC = (OP) ALL : SGI = (OP) ALL
The user bob may run anything on the SPARC and SGI machines as any user
listed in the OP Runas_Alias (root and operator.)
jim +biglab = ALL
The user jim may run any command on machines in the biglab netgroup.
sudo knows that "biglab" is a netgroup due to the `+' prefix.
+secretaries ALL = PRINTING, /usr/bin/adduser, /usr/bin/rmuser
Users in the secretaries netgroup need to help manage the printers as
well as add and remove users, so they are allowed to run those commands
on all machines.
fred ALL = (DB) NOPASSWD: ALL
The user fred can run commands as any user in the DB Runas_Alias (oracle
or sybase) without giving a password.
john ALPHA = /usr/bin/su [!-]*, !/usr/bin/su *root*
On the ALPHA machines, user john may su to anyone except root but he is
not allowed to specify any options to the su(1) command.
jen ALL, !SERVERS = ALL
The user jen may run any command on any machine except for those in the
SERVERS Host_Alias (primary, mail, www, and ns).
jill SERVERS = /usr/bin/, !SU, !SHELLS
For any machine in the SERVERS Host_Alias, jill may run any commands in
the directory /usr/bin/ except for those commands belonging to the SU and
SHELLS Cmnd_Aliases. While not specifically mentioned in the rule, the
commands in the PAGERS Cmnd_Alias all reside in /usr/bin and have the
noexec option set.
steve CSNETS = (operator) /usr/local/op_commands/
The user steve may run any command in the directory
/usr/local/op_commands/ but only as user operator.
matt valkyrie = KILL
On his personal workstation, valkyrie, matt needs to be able to kill hung
processes.
WEBADMIN www = (www) ALL, (root) /usr/bin/su www
On the host www, any user in the WEBADMIN User_Alias (will, wendy, and
wim), may run any command as user www (which owns the web pages) or
simply su(1) to www.
ALL CDROM = NOPASSWD: /sbin/umount /CDROM,\
/sbin/mount -o nosuid\,nodev /dev/cd0a /CDROM
Any user may mount or unmount a CD-ROM on the machines in the CDROM
Host_Alias (orion, perseus, hercules) without entering a password. This
is a bit tedious for users to type, so it is a prime candidate for
encapsulating in a shell script.
SECURITY NOTES
Limitations of the `!' operator
It is generally not effective to "subtract" commands from ALL using the
`!' operator. A user can trivially circumvent this by copying the
desired command to a different name and then executing that. For
example:
bill ALL = ALL, !SU, !SHELLS
Doesn't really prevent bill from running the commands listed in SU or
SHELLS since he can simply copy those commands to a different name, or
use a shell escape from an editor or other program. Therefore, these
kind of restrictions should be considered advisory at best (and
reinforced by policy).
In general, if a user has sudo ALL there is nothing to prevent them from
creating their own program that gives them a root shell (or making their
own copy of a shell) regardless of any `!' elements in the user
specification.
Security implications of fast_glob
If the fast_glob option is in use, it is not possible to reliably negate
commands where the path name includes globbing (aka wildcard) characters.
This is because the C library's fnmatch(3) function cannot resolve
relative paths. While this is typically only an inconvenience for rules
that grant privileges, it can result in a security issue for rules that
subtract or revoke privileges.
For example, given the following sudoers file entry:
john ALL = /usr/bin/passwd [a-zA-Z0-9]*, /usr/bin/chsh [a-zA-Z0-9]*,\
/usr/bin/chfn [a-zA-Z0-9]*, !/usr/bin/* root
User john can still run `/usr/bin/passwd root' if fast_glob is enabled by
changing to /usr/bin and running `./passwd root' instead.
Another potential issue is that when sudo executes the command, it must
use the command or path specified by the user instead of a path listed in
the sudoers file. This may lead to a time of check versus time of use
race condition.
Wildcards in command arguments
Command line arguments are matched as a single, concatenated string.
This mean a wildcard character such as `?' or `*' will match across word
boundaries, which may be unexpected. For example, while a sudoers entry
like:
%operator ALL = /bin/cat /var/log/messages*
will allow command like:
$ sudo cat /var/log/messages.1
It will also allow:
$ sudo cat /var/log/messages /etc/shadow
which is probably not what was intended. A safer alternative is to use a
regular expression for matching command line arguments. The above
example can be rewritten as a regular expression:
%operator ALL = /bin/cat ^/var/log/messages[^[:space:]]*$
The regular expression will only match a single file with a name that
begins with /var/log/messages and does not include any white space in the
name. It is often better to do command line processing outside of the
sudoers file in a scripting language for anything non-trivial.
Regular expressions in command names
Using a regular expression to match a command name has the same security
implications as using the fast_glob option:
o It is not possible to reliably negate commands when the path name is a
regular expression.
o When sudo executes the command, it must use the command or path
specified by the user instead of a path listed in the sudoers file.
This may lead to a time of check versus time of use race condition.
These issues do not apply to rules where only the command line options
are matched using a regular expression.
Preventing shell escapes
Once sudo executes a program, that program is free to do whatever it
pleases, including run other programs. This can be a security issue
since it is not uncommon for a program to allow shell escapes, which lets
a user bypass sudo's access control and logging. Common programs that
permit shell escapes include shells (obviously), editors, paginators,
mail, and terminal programs.
There are four basic approaches to this problem:
restrict Avoid giving users access to commands that allow the user to
run arbitrary commands. Many editors have a restricted mode
where shell escapes are disabled, though sudoedit is a better
solution to running editors via sudo. Due to the large number
of programs that offer shell escapes, restricting users to the
set of programs that do not is often unworkable.
intercept On most systems, sudo's intercept functionality can be used to
transparently intercept an attempt to run a new command, allow
or deny it based on sudoers rules, and log the result. For
example, this can be used to restrict the commands run from
within a privileged shell or editor. However, not all
programs operate correctly when intercept is enabled.
There are two underlying mechanisms that may be used to
implement intercept mode: dso and trace. The intercept_type
setting can be used to select between them.
The first mechanism, dso, overrides the standard C library
functions that are used to execute a command. It does this by
setting an environment variable (usually LD_PRELOAD) to the
path of a dynamic shared object, or shared library, containing
custom versions of the execve(2), execl(3), execle(3),
execlp(3), execv(3), execvp(3), execvpe(3), and system(3)
library functions that connect back to sudo for a policy
decision. Note, however, that this applies only to
dynamically-linked executables. It is not possible to
intercept commands for statically-linked executables or
executables that run under binary emulation this way. Because
most dynamic loaders ignore LD_PRELOAD (or the equivalent)
when running set-user-ID and set-group-ID programs, sudoers
will not permit such programs to be run in intercept mode by
default. The dso mechanism is incompatible with sudo's
SELinux RBAC support (but see below). SELinux disables
LD_PRELOAD by default and interferes with file descriptor
inheritance, which sudo relies on.
The second mechanism, trace, is available on Linux systems
that support seccomp(2) filtering. It uses ptrace(2) and
seccomp(2) to intercept the execve(2) system call instead of
pre-loading a dynamic shared object. Both static and dynamic
executables are supported and it is compatible with sudo's
SELinux RBAC mode. Functions utilizing the execveat(2) system
call, such as fexecve(3), are not currently intercepted.
Programs that rely on ptrace(2) themselves, such as debuggers
and system call tracers (such as strace(1) and truss(1)) will
be unable to function if intercept is enabled in trace mode.
This same restriction applies to the log_subcmds sudoers
option.
The intercept feature is known to work on Solaris, *BSD,
Linux, macOS, HP-UX 11.x and AIX 5.3 and above. It should be
supported on most operating systems that support the
LD_PRELOAD environment variable or an equivalent. It is not
possible to intercept shell built-in commands or restrict the
ability to read or write sensitive files from within a shell.
To enable intercept mode on a per-command basis, use the
INTERCEPT tag as documented in the User Specification section
above. Here is that example again:
chuck research = INTERCEPT: ALL
This allows user chuck to run any command on the machine
"research" in intercept mode. Any commands run via shell
escapes will be validated and logged by sudo. If you are
unsure whether or not your system is capable of supporting
intercept, you can always just try it out and check whether or
not external commands run via a shell are logged when
intercept is enabled.
There is an inherent race condition between when a command is
checked against sudoers rules and when it is actually
executed. If a user is allowed to run arbitrary commands,
they may be able to change the execve(2) arguments in the
program after the sudoers policy check has completed but
before the new command is executed. Starting with version
1.9.12, the trace method will verify that the command and its
arguments have not changed after execve(2) has completed but
before execution of the new program has had a chance to run.
This is not the case with the dso method. See the description
of the intercept_verify setting for more information.
log There are two separate but related ways to log additional
commands. The first is to enable I/O logging using the
log_output flag. This will log the command's output but will
not create an event log entry when the additional command is
run. The second is to enable the log_subcmds flag in sudoers
which will create an event log entry every time a new command
is run. If I/O logging is also enabled, the log entry will
include a time offset into the I/O log to indicate when the
command was run. This offset can be passed to the
sudoreplay(8) utility to replay the I/O log at the exact
moment when the command was run. The log_subcmds flag uses
the same mechanism as intercept (see above) and has the same
limitations.
noexec sudo's noexec functionality can be used to prevent a program
run by sudo from executing any other programs. On most
systems, it uses the same LD_PRELOAD mechanism as intercept
(see above) and thus the same caveats apply. The noexec
functionality is capable of blocking execution of commands run
via the execve(2), execl(3), execle(3), execlp(3), exect(3),
execv(3), execveat(3), execvP(3), execvp(3), execvpe(3),
fexecve(3), popen(3), posix_spawn(3), posix_spawnp(3),
system(3), and wordexp(3) functions. On Linux, a seccomp(2)
filter is used to implement noexec. On Solaris 10 and higher,
noexec uses Solaris privileges instead of the LD_PRELOAD
environment variable.
To enable noexec for a command, use the NOEXEC tag as
documented in the User Specification section above. Here is
that example again:
aaron shanty = NOEXEC: /usr/bin/more, /usr/bin/vi
This allows user aaron to run /usr/bin/more and /usr/bin/vi
with noexec enabled. This will prevent those two commands
from executing other commands (such as a shell). If you are
unsure whether or not your system is capable of supporting
noexec you can always just try it out and check whether shell
escapes work when noexec is enabled.
Restricting shell escapes is not a panacea. Programs running as root are
still capable of many potentially hazardous operations (such as changing
or overwriting files) that could lead to unintended privilege escalation.
In the specific case of an editor, a safer approach is to give the user
permission to run sudoedit (see below).
Secure editing
The sudoers plugin includes sudoedit support which allows users to
securely edit files with the editor of their choice. As sudoedit is a
built-in command, it must be specified in the sudoers file without a
leading path. However, it may take command line arguments just as a
normal command does. Wildcards used in sudoedit command line arguments
are expected to be path names, so a forward slash (`/') will not be
matched by a wildcard.
Unlike other sudo commands, the editor is run with the permissions of the
invoking user and with the environment unmodified. More information may
be found in the description of the -e option in sudo(8).
For example, to allow user operator to edit the "message of the day" file
on any machine:
operator ALL = sudoedit /etc/motd
The operator user then runs sudoedit as follows:
$ sudoedit /etc/motd
The editor will run as the operator user, not root, on a temporary copy
of /etc/motd. After the file has been edited, /etc/motd will be updated
with the contents of the temporary copy.
Users should never be granted sudoedit permission to edit a file that
resides in a directory the user has write access to, either directly or
via a wildcard. If the user has write access to the directory it is
possible to replace the legitimate file with a link to another file,
allowing the editing of arbitrary files. To prevent this, starting with
version 1.8.16, symbolic links will not be followed in writable
directories and sudoedit will refuse to edit a file located in a writable
directory unless the sudoedit_checkdir option has been disabled or the
invoking user is root. Additionally, in version 1.8.15 and higher,
sudoedit will refuse to open a symbolic link unless either the
sudoedit_follow option is enabled or the sudoedit command is prefixed
with the FOLLOW tag in the sudoers file.
Time stamp file checks
sudoers will check the ownership of its time stamp directory
(/opt/local/var/run/sudo/ts by default) and ignore the directory's
contents if it is not owned by root or if it is writable by a user other
than root. Older versions of sudo stored time stamp files in /tmp; this
is no longer recommended as it may be possible for a user to create the
time stamp themselves on systems that allow unprivileged users to change
the ownership of files they create.
While the time stamp directory should be cleared at reboot time, not all
systems contain a /run or /var/run directory. To avoid potential
problems, sudoers will ignore time stamp files that date from before the
machine booted on systems where the boot time is available.
Some systems with graphical desktop environments allow unprivileged users
to change the system clock. Since sudoers relies on the system clock for
time stamp validation, it may be possible on such systems for a user to
run sudo for longer than timestamp_timeout by setting the clock back. To
combat this, sudoers uses a monotonic clock (which never moves backwards)
for its time stamps if the system supports it.
sudoers will not honor time stamps set far in the future. Time stamps
with a date greater than current_time + 2 * TIMEOUT will be ignored and
sudoers will log and complain.
If the timestamp_type option is set to "tty", the time stamp record
includes the device number of the terminal the user authenticated with.
This provides per-terminal granularity but time stamp records may still
outlive the user's session.
Unless the timestamp_type option is set to "global", the time stamp
record also includes the session ID of the process that last
authenticated. This prevents processes in different terminal sessions
from using the same time stamp record. On systems where a process's
start time can be queried, the start time of the session leader is
recorded in the time stamp record. If no terminal is present or the
timestamp_type option is set to "ppid", the start time of the parent
process is used instead. In most cases this will prevent a time stamp
record from being reused without the user entering a password when
logging out and back in again.
DEBUGGING
Versions 1.8.4 and higher of the sudoers plugin support a flexible
debugging framework that can help track down what the plugin is doing
internally if there is a problem. This can be configured in the
sudo.conf(5) file.
The sudoers plugin uses the same debug flag format as the sudo front-end:
subsystem@priority.
The priorities used by sudoers, in order of decreasing severity, are:
crit, err, warn, notice, diag, info, trace, and debug. Each priority,
when specified, also includes all priorities higher than it. For
example, a priority of notice would include debug messages logged at
notice and higher.
The following subsystems are used by the sudoers plugin:
alias User_Alias, Runas_Alias, Host_Alias and Cmnd_Alias processing
all matches every subsystem
audit BSM and Linux audit code
auth user authentication
defaults sudoers file Defaults settings
env environment handling
ldap LDAP-based sudoers
logging logging support
match matching of users, groups, hosts, and netgroups in the sudoers
file
netif network interface handling
nss network service switch handling in sudoers
parser sudoers file parsing
perms permission setting
plugin The equivalent of main for the plugin.
pty pseudo-terminal related code
rbtree redblack tree internals
sssd SSSD-based sudoers
util utility functions
For example:
Debug sudoers.so /var/log/sudoers_debug match@info,nss@info
For more information, see the sudo.conf(5) manual.
SEE ALSO
ssh(1), su(1), fnmatch(3), glob(3), mktemp(3), strftime(3), sudo.conf(5),
sudo_logsrv.proto(5), sudo_plugin(5), sudoers.ldap(5),
sudoers_timestamp(5), sudo(8), sudo_logsrvd(8), visudo(8)
AUTHORS
Many people have worked on sudo over the years; this version consists of
code written primarily by:
Todd C. Miller
See the CONTRIBUTORS.md file in the sudo distribution
(https://www.sudo.ws/about/contributors/) for an exhaustive list of
people who have contributed to sudo.
CAVEATS
The sudoers file should always be edited by the visudo utility which
locks the file and checks for syntax errors. If sudoers contains syntax
errors, sudo may refuse to run, which is a serious problem if sudo is
your only method of obtaining superuser privileges. Recent versions of
sudoers will attempt to recover after a syntax error by ignoring the rest
of the line after encountering an error. Older versions of sudo will not
run if sudoers contains a syntax error.
When using netgroups of machines (as opposed to users), if you store
fully qualified host name in the netgroup (as is usually the case), you
either need to have the machine's host name be fully qualified as
returned by the hostname command or use the fqdn option in sudoers.
BUGS
If you believe you have found a bug in sudoers, you can either file a bug
report in the sudo bug database, https://bugzilla.sudo.ws/, or open an
issue at https://github.com/sudo-project/sudo/issues. If you would
prefer to use email, messages may be sent to the sudo-workers mailing
list, https://www.sudo.ws/mailman/listinfo/sudo-workers (public) or
<sudo@sudo.ws> (private).
Please not report security vulnerabilities through public GitHub issues,
Bugzilla or mailing lists. Instead, report them via email to
<Todd.Miller@sudo.ws>. You may encrypt your message with PGP if you
would like, using the key found at https://www.sudo.ws/dist/PGPKEYS.
SUPPORT
Limited free support is available via the sudo-users mailing list, see
https://www.sudo.ws/mailman/listinfo/sudo-users to subscribe or search
the archives.
DISCLAIMER
sudo is provided "AS IS" and any express or implied warranties,
including, but not limited to, the implied warranties of merchantability
and fitness for a particular purpose are disclaimed. See the LICENSE.md
file distributed with sudo or https://www.sudo.ws/about/license/ for
complete details.
Sudo 1.9.16 July 14, 2024 Sudo 1.9.16
sudo 1.9.16 - Generated Mon Sep 2 15:31:53 CDT 2024