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PROLOG
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.
NAME
who — display who is on the system
SYNOPSIS
who [-mTu] [-abdHlprt] [file]
who [-mu] -s [-bHlprt] [file]
who -q [file]
who am i
who am I
DESCRIPTION
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.
OPTIONS
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.
OPERANDS
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.
STDIN
Not used.
INPUT FILES
None.
ENVIRONMENT VARIABLES
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.
ASYNCHRONOUS EVENTS
Default.
STDOUT
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.
STDERR
The standard error shall be used only for diagnostic messages.
OUTPUT FILES
None.
EXTENDED DESCRIPTION
None.
EXIT STATUS
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
CONSEQUENCES OF ERRORS
Default.
The following sections are informative.
APPLICATION USAGE
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.
EXAMPLES
None.
RATIONALE
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.
FUTURE DIRECTIONS
None.
SEE ALSO
mesg
The Base Definitions volume of POSIX.1‐2017, Chapter 8, Environment Variables, Section
12.2, Utility Syntax Guidelines
COPYRIGHT
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 .