chmod(1) User Commands chmod(1)
NAME
chmod - change file mode bits
SYNOPSIS
chmod [OPTION]... MODE[,MODE]... FILE...
chmod [OPTION]... OCTAL-MODE FILE...
chmod [OPTION]... --reference=RFILE FILE...
DESCRIPTION
This manual page documents the GNU version of chmod. chmod changes the
file mode bits of each given file according to mode, which can be either
a symbolic representation of changes to make, or an octal number
representing the bit pattern for the new mode bits.
The format of a symbolic mode is [ugoa...][[-+=][perms...]...], where
perms is either zero or more letters from the set rwxXst, or a single
letter from the set ugo. Multiple symbolic modes can be given, separated
by commas.
A combination of the letters ugoa controls which users' access to the
file will be changed: the user who owns it (u), other users in the file's
group (g), other users not in the file's group (o), or all users (a). If
none of these are given, the effect is as if (a) were given, but bits
that are set in the umask are not affected.
The operator + causes the selected file mode bits to be added to the
existing file mode bits of each file; - causes them to be removed; and =
causes them to be added and causes unmentioned bits to be removed except
that a directory's unmentioned set user and group ID bits are not
affected.
The letters rwxXst select file mode bits for the affected users: read
(r), write (w), execute (or search for directories) (x), execute/search
only if the file is a directory or already has execute permission for
some user (X), set user or group ID on execution (s), restricted deletion
flag or sticky bit (t). Instead of one or more of these letters, you can
specify exactly one of the letters ugo: the permissions granted to the
user who owns the file (u), the permissions granted to other users who
are members of the file's group (g), and the permissions granted to users
that are in neither of the two preceding categories (o).
A numeric mode is from one to four octal digits (0-7), derived by adding
up the bits with values 4, 2, and 1. Omitted digits are assumed to be
leading zeros. The first digit selects the set user ID (4) and set group
ID (2) and restricted deletion or sticky (1) attributes. The second
digit selects permissions for the user who owns the file: read (4), write
(2), and execute (1); the third selects permissions for other users in
the file's group, with the same values; and the fourth for other users
not in the file's group, with the same values.
chmod never changes the permissions of symbolic links; the chmod system
call cannot change their permissions. This is not a problem since the
permissions of symbolic links are never used. However, for each symbolic
link listed on the command line, chmod changes the permissions of the
pointed-to file. In contrast, chmod ignores symbolic links encountered
during recursive directory traversals.
SETUID AND SETGID BITS
chmod clears the set-group-ID bit of a regular file if the file's group
ID does not match the user's effective group ID or one of the user's
supplementary group IDs, unless the user has appropriate privileges.
Additional restrictions may cause the set-user-ID and set-group-ID bits
of MODE or RFILE to be ignored. This behavior depends on the policy and
functionality of the underlying chmod system call. When in doubt, check
the underlying system behavior.
For directories chmod preserves set-user-ID and set-group-ID bits unless
you explicitly specify otherwise. You can set or clear the bits with
symbolic modes like u+s and g-s. To clear these bits for directories
with a numeric mode requires an additional leading zero like 00755,
leading minus like -6000, or leading equals like =755.
RESTRICTED DELETION FLAG OR STICKY BIT
The restricted deletion flag or sticky bit is a single bit, whose
interpretation depends on the file type. For directories, it prevents
unprivileged users from removing or renaming a file in the directory
unless they own the file or the directory; this is called the restricted
deletion flag for the directory, and is commonly found on world-writable
directories like /tmp. For regular files on some older systems, the bit
saves the program's text image on the swap device so it will load more
quickly when run; this is called the sticky bit.
OPTIONS
Change the mode of each FILE to MODE. With --reference, change the mode
of each FILE to that of RFILE.
-c, --changes
like verbose but report only when a change is made
-f, --silent, --quiet
suppress most error messages
-v, --verbose
output a diagnostic for every file processed
--no-preserve-root
do not treat '/' specially (the default)
--preserve-root
fail to operate recursively on '/'
--reference=RFILE
use RFILE's mode instead of specifying MODE values. RFILE is
always dereferenced if a symbolic link.
-R, --recursive
change files and directories recursively
--help display this help and exit
--version
output version information and exit
Each MODE is of the form '[ugoa]*([-+=]([rwxXst]*|[ugo]))+|[-+=][0-7]+'.
AUTHOR
Written by David MacKenzie and Jim Meyering.
REPORTING BUGS
GNU coreutils online help: <https://www.gnu.org/software/coreutils/>
Report any translation bugs to <https://translationproject.org/team/>
COPYRIGHT
Copyright © 2023 Free Software Foundation, Inc. License GPLv3+: GNU GPL
version 3 or later <https://gnu.org/licenses/gpl.html>.
This is free software: you are free to change and redistribute it. There
is NO WARRANTY, to the extent permitted by law.
SEE ALSO
chmod(1)
Full documentation <https://www.gnu.org/software/coreutils/chmod>
or available locally via: info '(coreutils) chmod invocation'
GNU coreutils 9.2 March 2023 chmod(1)
coreutils 9.2 - Generated Fri Mar 31 05:48:00 CDT 2023