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PROLOG | NAME | SYNOPSIS | DESCRIPTION | OPTIONS | OPERANDS | STDIN | INPUT FILES | ENVIRONMENT VARIABLES | ASYNCHRONOUS EVENTS | STDOUT | STDERR | OUTPUT FILES | EXTENDED DESCRIPTION | EXIT STATUS | CONSEQUENCES OF ERRORS | APPLICATION USAGE | EXAMPLES | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT |
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WHO(1P) POSIX Programmer's Manual WHO(1P)
This manual page is part of the POSIX Programmer's Manual. The
Linux implementation of this interface may differ (consult the
corresponding Linux manual page for details of Linux behavior), or
the interface may not be implemented on Linux.
who — display who is on the system
who [-mTu] [-abdHlprt] [file]
who [-mu] -s [-bHlprt] [file]
who -q [file]
who am i
who am I
The who utility shall list various pieces of information about
accessible users. The domain of accessibility is implementation-
defined.
Based on the options given, who can also list the user's name,
terminal line, login time, elapsed time since activity occurred on
the line, and the process ID of the command interpreter for each
current system user.
The who utility shall conform to the Base Definitions volume of
POSIX.1‐2017, Section 12.2, Utility Syntax Guidelines.
The following options shall be supported. The metavariables, such
as <line>, refer to fields described in the STDOUT section.
-a Process the implementation-defined database or named
file with the -b, -d, -l, -p, -r, -t, -T and -u options
turned on.
-b Write the time and date of the last system reboot. The
system reboot time is the time at which the
implementation is able to commence running processes.
-d Write a list of all processes that have expired and not
been respawned by the init system process. The <exit>
field shall appear for dead processes and contain the
termination and exit values of the dead process. This
can be useful in determining why a process terminated.
-H Write column headings above the regular output.
-l (The letter ell.) List only those lines on which the
system is waiting for someone to login. The <name> field
shall be LOGIN in such cases. Other fields shall be the
same as for user entries except that the <state> field
does not exist.
-m Output only information about the current terminal.
-p List any other process that is currently active and has
been previously spawned by init.
-q (Quick.) List only the names and the number of users
currently logged on. When this option is used, all other
options shall be ignored.
-r Write the current run-level of the init process.
-s List only the <name>, <line>, and <time> fields. This
is the default case.
-t Indicate the last change to the system clock.
-T Show the state of each terminal, as described in the
STDOUT section.
-u Write ``idle time'' for each displayed user in addition
to any other information. The idle time is the time
since any activity occurred on the user's terminal. The
method of determining this is unspecified. This option
shall list only those users who are currently logged in.
The <name> is the user's login name. The <line> is the
name of the line as found in the directory /dev. The
<time> is the time that the user logged in. The
<activity> is the number of hours and minutes since
activity last occurred on that particular line. A dot
indicates that the terminal has seen activity in the
last minute and is therefore ``current''. If more than
twenty-four hours have elapsed or the line has not been
used since boot time, the entry shall be marked <old>.
This field is useful when trying to determine whether a
person is working at the terminal or not. The <pid> is
the process ID of the user's login process.
The following operands shall be supported:
am i, am I
In the POSIX locale, limit the output to describing the
invoking user, equivalent to the -m option. The am and i
or I must be separate arguments.
file Specify a pathname of a file to substitute for the
implementation-defined database of logged-on users that
who uses by default.
Not used.
None.
The following environment variables shall affect the execution of
who:
LANG Provide a default value for the internationalization
variables that are unset or null. (See the Base
Definitions volume of POSIX.1‐2017, Section 8.2,
Internationalization Variables for the precedence of
internationalization variables used to determine the
values of locale categories.)
LC_ALL If set to a non-empty string value, override the values
of all the other internationalization variables.
LC_CTYPE Determine the locale for the interpretation of sequences
of bytes of text data as characters (for example,
single-byte as opposed to multi-byte characters in
arguments).
LC_MESSAGES
Determine the locale that should be used to affect the
format and contents of diagnostic messages written to
standard error.
LC_TIME Determine the locale used for the format and contents of
the date and time strings.
NLSPATH Determine the location of message catalogs for the
processing of LC_MESSAGES.
TZ Determine the timezone used when writing date and time
information. If TZ is unset or null, an unspecified
default timezone shall be used.
Default.
The who utility shall write its default format to the standard
output in an implementation-defined format, subject only to the
requirement of containing the information described above.
XSI-conformant systems shall write the default information to the
standard output in the following general format:
<name>[<state>]<line><time>[<activity>][<pid>][<comment>][<exit>]
For the -b option, <line> shall be "systemboot". The <name> is
unspecified.
The following format shall be used for the -T option:
"%s %c %s %s\n" <name>, <terminal state>, <terminal name>,
<time of login>
where <terminal state> is one of the following characters:
+ The terminal allows write access to other users.
- The terminal denies write access to other users.
? The terminal write-access state cannot be determined.
<space> This entry is not associated with a terminal.
In the POSIX locale, the <time of login> shall be equivalent in
format to the output of:
date +"%b %e %H:%M"
If the -u option is used with -T, the idle time shall be added to
the end of the previous format in an unspecified format.
The standard error shall be used only for diagnostic messages.
None.
None.
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
Default.
The following sections are informative.
The name init used for the system process is the most commonly
used on historical systems, but it may vary.
The ``domain of accessibility'' referred to is a broad concept
that permits interpretation either on a very secure basis or even
to allow a network-wide implementation like the historical rwho.
None.
Due to differences between historical implementations, the base
options provided were a compromise to allow users to work with
those functions. The standard developers also considered removing
all the options, but felt that these options offered users
valuable functionality. Additional options to match historical
systems are available on XSI-conformant systems.
It is recognized that the who command may be of limited
usefulness, especially in a multi-level secure environment. The
standard developers considered, however, that having some standard
method of determining the ``accessibility'' of other users would
aid user portability.
No format was specified for the default who output for systems not
supporting the XSI option. In such a user-oriented command,
designed only for human use, this was not considered to be a
deficiency.
The format of the terminal name is unspecified, but the
descriptions of ps, talk, and write require that they use the same
format.
It is acceptable for an implementation to produce no output for an
invocation of who mil.
None.
mesg(1p)
The Base Definitions volume of POSIX.1‐2017, Chapter 8,
Environment Variables, Section 12.2, Utility Syntax Guidelines
Portions of this text are reprinted and reproduced in electronic
form from IEEE Std 1003.1-2017, Standard for Information
Technology -- Portable Operating System Interface (POSIX), The
Open Group Base Specifications Issue 7, 2018 Edition, Copyright
(C) 2018 by the Institute of Electrical and Electronics Engineers,
Inc and The Open Group. In the event of any discrepancy between
this version and the original IEEE and The Open Group Standard,
the original IEEE and The Open Group Standard is the referee
document. The original Standard can be obtained online at
http://www.opengroup.org/unix/online.html .
Any typographical or formatting errors that appear in this page
are most likely to have been introduced during the conversion of
the source files to man page format. To report such errors, see
https://www.kernel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2017 WHO(1P)
Pages that refer to this page: id(1p), logname(1p), talk(1p), write(1p)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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