who (Unix)

The standard Unix command who displays a list of users who are currently logged into the computer.

The who command is related to the command w, which provides the same information but also displays additional data and statistics.

Specification

The Single Unix Specification (SUS) specifies that who should list information about accessible users. The XSI extension also specifies that the data of the username, terminal, login time, process ID, and time since last activity occurred on the terminal, furthermore, an alternate system database used for user information can be specified as an optional argument to who.

The command can be invoked with the arguments am i or am I (so it is invoked as who am i or who am I), showing information about the current terminal only (see the command tty and the -m option below, of which this invocation is equivalent).

Usage

The SUS without extensions only specifies the following -m, -T, and -u options, all other options are specified in the XSI extension.

-a, process the system database used for user information with the -b, -d, -l, -p, -r, -t, -T and -u.

-b, show time when system was last rebooted

-d, show zombie processes and details

-H, show column headers

-l, show terminals where a user can log in

-m, show information about the current terminal only

-p, show active processes

-q, quick format, show only names and the number of all users logged on, disables all other options; equivalent to users command line utility

-r, show runlevel of the init process.

-s, (default) show only name, terminal, and time details

-t, show when system clock was last changed

-T, show details of each terminal in a standard format (see note in Examples section)

-u, show idle time; XSI shows users logged in and displays information whether the terminal has been used recently or not

Other Unix and Unix-like operating systems may add extra options. GNU who includes a -i option behaving similarly to -u and a -w option displaying whether the user listed accepts messages (the SUS displays this when -T is specified), yet GNU who and BSD who both omit a number of the above options (such as -a, -b, -d, and others); GNU who instead uses -l to perform DNS lookups on hostnames listed.

Output

The SUS without extensions specifies that the output format is to be "implementation-defined". The XSI extension specifies a format, but notes that it is not fully specified; delimiters and field lengths are not precisely specified. Thus, the format of the output differs considerably among Unix implementations.

External links

who — specification from the Single Unix Specification
who — manual page from GNU coreutils
who — manual page from OpenBSD

Unix command-line interface programs and shell builtins

File system	cat chmod chown chgrp cksum cmp cp dd du df file fsck fuser ln ls mkdir mount mv pax pwd rm rmdir split tee touch type umask

Processes	at bg chroot cron fg kill killall nice pgrep pkill ps pstree time top

User environment	clear env exit finger history logname mesg passwd su sudo uptime talk tput uname w wall who whoami write

Text processing	awk banner basename comm csplit cut diff dirname ed ex fmt fold head iconv join less more nl paste printf sed sort spell strings tail tr uniq vi wc xargs yes

Shell builtins	alias cd echo test unset wait

Networking	dig host ifconfig inetd netcat netstat nslookup ping rdate rlogin route ssh traceroute

Searching	find grep locate whatis whereis

Documentation	apropos help man

Miscellaneous	bc dc cal expr lp od sleep true and false

List of Unix commands

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who (Unix)

Specification

Usage

Output

See also

External links