WHO(1) General Commands Manual WHO(1)

who — display who is on the system

who [-abHmqsTu] [am I] [file]

The who utility displays information about currently logged in users. By default, this includes the login name, tty name, date and time of login and remote hostname if not local.

The options are as follows:

Equivalent to -bTu, with the exception that output is not restricted to the time and date of the last system reboot.
Write the time and date of the last system reboot.
Write column headings above the output.
Show information about the terminal attached to standard input only.
“Quick mode”: List the names and number of logged in users in columns. All other command line options are ignored.
Show the name, line and time fields only. This is the default.
Indicate whether each user is accepting messages. One of the following characters is written:

User is accepting messages.
User is not accepting messages.
An error occurred.
Show idle time for each user in hours and minutes as hh:mm, ‘.’ if the user has been idle less than a minute, and “old” if the user has been idle more than 24 hours.
Equivalent to -m.

By default, who gathers information from the file /var/run/utmpx. An alternate file may be specified which is usually /var/log/utx.log (or /var/log/utx.log.[0-6] depending on site policy as utx.log can grow quite large and daily versions may or may not be kept around after compression by ac(8)). The utx.log file contains a record of every login, logout, crash, shutdown and date change since utx.log was last truncated or created.

If /var/log/utx.log is being used as the file, the user name may be empty or one of the special characters '|', '}' and '~'. Logouts produce an output line without any user name. For more information on the special characters, see getutxent(3).

The COLUMNS, LANG, LC_ALL and LC_TIME environment variables affect the execution of who as described in environ(7).

/var/run/utmpx
 

The who utility exits 0 on success, and >0 if an error occurs.

Show a brief summary of who is logged in:

$ who -q
fernape          root             root
# users = 3

Show who is logged in along with the line and time fields (without the headers):

$ who -s
fernape          ttyv0        Aug 26 16:23
root             ttyv1        Aug 26 16:23
root             ttyv2        Aug 26 16:23

Show information about the terminal attached to standard input:

$ who am i
fernape                       Aug 26 16:24

Show time and date of the last system reboot, whether the users accept messages and the idle time for each of them:

$ who -a
                 - system boot  Aug 26 16:23   .
fernape          - ttyv0        Aug 26 16:23   .
root             - ttyv1        Aug 26 16:23   .
root             - ttyv2        Aug 26 16:23   .

Same as above but showing headers:

$ who -aH
NAME             S LINE         TIME         IDLE  FROM
                 - system boot  Aug 26 16:23   .
fernape          - ttyv0        Aug 26 16:23   .
root             - ttyv1        Aug 26 16:23 00:01
root             - ttyv2        Aug 26 16:23 00:01

last(1), users(1), w(1), getutxent(3)

The who utility conforms to IEEE Std 1003.1-2001 (“POSIX.1”).

A who command appeared in Version 1 AT&T UNIX.

August 30, 2020 macOS 15.2