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20.6 who: Print who is currently logged in

who prints information about users who are currently logged on. Synopsis:

who [option] [file] [am i]

If given no non-option arguments, who prints the following information for each user currently logged on: login name, terminal line, login time, and remote hostname or X display.

If given one non-option argument, who uses that instead of a default system-maintained file (often ‘/var/run/utmp’ or ‘/etc/utmp’) as the name of the file containing the record of users logged on. ‘/var/log/wtmp’ is commonly given as an argument to who to look at who has previously logged on.

If given two non-option arguments, who prints only the entry for the user running it (determined from its standard input), preceded by the hostname. Traditionally, the two arguments given are ‘am i’, as in ‘who am i’.

Time stamps are listed according to the time zone rules specified by the TZ environment variable, or by the system default rules if TZ is not set. See (libc)TZ Variable section `Specifying the Time Zone with TZ' in The GNU C Library.

The program accepts the following options. Also see Common options.


Same as ‘-b -d --login -p -r -t -T -u’.


Print the date and time of last system boot.


Print information corresponding to dead processes.


Print column headings.


Same as ‘who am i’.


Print only the login names and the number of users logged on. Overrides all other options.


Ignored; for compatibility with other versions of who.


After the login time, print the number of hours and minutes that the user has been idle. ‘.’ means the user was active in the last minute. ‘old’ means the user has been idle for more than 24 hours.


List only the entries that correspond to processes via which the system is waiting for a user to login. The user name is always ‘LOGIN’.


Attempt to canonicalize hostnames found in utmp through a DNS lookup. This is not the default because it can cause significant delays on systems with automatic dial-up internet access.


Print a line of column headings.


After each login name print a character indicating the user's message status:

+’ allowing write messages
‘-’ disallowing write messages
‘?’ cannot find terminal device

An exit status of zero indicates success, and a nonzero value indicates failure.

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