The Linux who command lists login sessions recorded as active by the system. It typically shows each user’s login name, terminal, login time, and remote host or display when available. Use who -q for a quick count, or who -m to show the session associated with your current terminal.
What the who command does
GNU Coreutils describes who as a command that “prints information about users who are currently logged on.” It reads system login-accounting records, usually in a utmp-style file such as /var/run/utmp. Its output reflects the records available there—not a universal inventory of every running process or every kind of graphical session. If those records are missing or incomplete, the output may be empty or may omit sessions that another system component knows about.
A typical record includes a login name, terminal line, login time, and remote hostname or X display if one is recorded. The exact fields and behavior can vary with the system’s utmp/utmpx implementation. GNU Coreutils: who invocation
Basic syntax
who [OPTION]... [FILE]
who am iWith no file argument, who reads the default current-login record file. Supplying a file makes that file the input. The traditional who am i form (also who am I) and the -m option select the entry associated with the current terminal. Linux man-pages: who(1)
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Useful who options
| Command | What it shows |
|---|---|
who |
Recorded active login sessions and their available user, terminal, time, and host/display details. |
who -H |
Adds column headings to the output. |
who -q |
Prints login names and a count of users. This option overrides other options. |
who -u |
Adds idle time. GNU documents . for activity within the last minute and old for more than 24 hours idle. |
who -b |
Shows the last system boot. |
who -r |
Shows the current runlevel and, where applicable, a previous runlevel. |
who -T or who -w |
Shows message status after each login name: +, -, or ?. |
who -a |
Combines boot, dead-process, login-process, runlevel, clock-change, message, and user information options. |
who -m or who am i |
Shows the session associated with the invoking terminal. |
Option details are documented in the GNU Coreutils manual and the Linux who manual.
Examples for common tasks
List recorded sessions
whoUse this to see the sessions represented in the default login-record file. Add headings if you want labeled columns:
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who -HCount logged-in users
who -qThis prints the login names and a user count rather than the usual detailed session listing. It counts what the command reads from its accounting records, not every process on the machine.
Check idle time
who -uThe additional idle-time field is useful for spotting recorded sessions with no recent terminal activity. GNU’s documented markers are . for activity within the last minute and old for more than 24 hours idle.
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Show your terminal-associated session
who am i
who -mBoth forms focus on the login entry for the terminal from which you run the command. They are different from a general listing of all recorded sessions.
Inspect a supplied login-record file
who /var/log/wtmpA file argument changes the input from the default current-login records to the specified file. /var/log/wtmp is commonly used for historical login records when it exists and is accessible. The result depends on the contents and format of that file; it is not the default current-session view.
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Check boot or runlevel information
who -b
who -r-b reports the last system boot recorded. -r reports runlevel information available in the accounting records.
Time zones, host lookup, and portability
Timestamps use the TZ environment variable when it is set; otherwise, the system’s time-zone rules apply. GNU’s --lookup option requests DNS canonicalization of hostnames. It is not the default because DNS lookups can delay output. GNU Coreutils: who invocation
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The command is not guaranteed to be available or behave identically on every Unix-like platform. GNU notes that it is installed where a POSIX <utmpx.h> facility or equivalent exists; POSIX also leaves aspects of the accessible-user domain and behavior implementation-defined. POSIX: who
Quick Recap
What who does not tell you
- It does not list every process running on the system; it reports login-accounting entries.
- It does not guarantee that all interactive or graphical sessions appear. Missing or incomplete accounting records can leave sessions out.
- Its user count is a count from the records it reads, so it should be interpreted as a count of recorded logins rather than a definitive count of everyone currently using the machine.
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