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’.

Timestamps 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 Specifying the Time Zone with TZ in The GNU C Library Reference Manual.

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

‘-a’ ¶

‘--all’

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

‘-b’ ¶

‘--boot’

Print the date and time of last system boot.

‘-d’ ¶

‘--dead’

Print information corresponding to dead processes.

‘-H’ ¶

‘--heading’

Print a line of column headings.

‘-l’ ¶

‘--login’

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’.

‘--lookup’ ¶

Attempt to canonicalize hostnames found in utmp through a DNS lookup. This is not the default because of potential delays.

‘-m’ ¶

Same as ‘who am i’.

‘-p’ ¶

‘--process’

List active processes spawned by init.

‘-q’ ¶

‘--count’

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

‘-r’ ¶

‘--runlevel’

Print the current (and maybe previous) run-level of the init process.

‘-s’ ¶

Ignored; for compatibility with other versions of who.

‘-t’ ¶

‘--time’

Print last system clock change.

‘-u’ ¶

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.

‘-w’ ¶

‘-T’

‘--mesg’

‘--message’

‘--writable’

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

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

The who command is installed only on platforms with the POSIX <utmpx.h> include file or equivalent, so portable scripts should not rely on its existence on non-POSIX platforms.

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