Who (Unix)
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- The correct title of this article is who (Unix). The initial letter is shown capitalized due to technical restrictions.
The standard Unix command who displays a list of users who are currently logged into a computer.
The who command is related to the command w, which provides the same information but also displays additional data and statistics.
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[edit] 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 am I), showing information about the current terminal only (see the -m option below, of which this invocation is equivalent).
[edit] 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.
[edit] Examples
The SUS without extensions specifies that the output format is to be "implementation-defined"; the XSI extension specifies a format (see the specification document), but notes that the output format is not fully specified (delimiters and field lengths are not precisely specified).
Thus, the format of the output differs considerably between Unix implementations.
Headings added for clarity
$ who User tty login@ PCPU unixguy pts/4 Oct 20 15:35 (wrk1.foo.com) user2 pts/11 Oct 18 14:05 (wrk2.foo.com)
$ who -a Name [state] line time [idle] [pid] [comment] [exit] . system boot Sep 15 10:42 . run-level 3 Sep 15 10:43 3 0 S rc2 . Sep 15 10:45 old 153 id= s2 term=0 exit=0 LOGIN console Oct 5 13:20 3:42 28779 unixguy pts/1 Oct 19 12:05 0:04 12453 id=ts/1 term=0 exit=0
user19 pts/35 Apr 18 08:40 (localhost) user28 pts/27 Apr 18 09:50 (localhost)
jsmith pts/124 Apr 11 11:04 pjones pts/125 Apr 11 11:08
mjones pts/0 Apr 18 10:01 tlin pts/2 Apr 17 15:17
jsare console Apr 18 09:50 jsare ttyp1 Apr 18 10:01 admin ttyp2 Apr 17 15:17
[edit] See also
| Unix command line programs (more) | |||
| File and file system management: | cat | cd | chmod | chown | chgrp | cp | du | df | file | fsck | ln | ls | lsof | mkdir | more | mount | mv | pwd | rm | rmdir | split | touch | tree | ||
| Process management: | anacron | at | chroot | crontab | kill | killall | nice | pgrep | pidof | pkill | ps | sleep | screen | time | timex | top | wait | ||
| User Management/Environment: | env | finger | id | locale | mesg | passwd | su | sudo | uname | uptime | w | wall | who | whoami | write | ||
| Text processing: | awk | cut | diff | ex | head | iconv | join | less | more | nkf | paste | sed | sort | tail | tr | uniq | wc | xargs | ||
| Shell programming: | echo | expr | printf | unset | Printing: | lp |
| Communications: inetd | netstat | ping | rlogin | traceroute |
Searching: find | grep | strings |
Miscellaneous: banner | bc | cal | man | size | yes |
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[edit] External links
- who -- specification from the Single Unix Specification
