WHO(P) POSIX Programmer's Manual WHO(P)
who - display who is on the system
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 inter-
preter for each current system user.
The who utility shall conform to the Base Definitions volume of IEEE Std 1003.1-2001, Sec-
tion 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 reboot.
-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
-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 activ-
ity 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 per-
son is working at the terminal or not. The <pid> is the process ID of the user's
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.
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 IEEE Std 1003.1-2001, Section 8.2, Inter-
nationalization 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 interna-
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 argu-
Determine the locale that should be used to affect the format and contents of diag-
nostic messages written to standard error.
Determine the locale used for the format and contents of the date and time strings.
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.
The who utility shall write its default format to the standard output in an implementa-
tion-defined format, subject only to the requirement of containing the information
XSI-conformant systems shall write the default information to the standard output in the
following general format:
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.
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.
The following exit values shall be returned:
0 Successful completion.
>0 An error occurred.
CONSEQUENCES OF ERRORS
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 his-
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 con-
sidered removing all the options, but felt that these options offered users valuable func-
tionality. Additional options to match historical systems are available on XSI-conformant
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 portabil-
No format was specified for the default who output for systems not supporting the XSI
Extension. In such a user-oriented command, designed only for human use, this was not con-
sidered 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.
Portions of this text are reprinted and reproduced in electronic form from IEEE Std
1003.1, 2003 Edition, Standard for Information Technology -- Portable Operating System
Interface (POSIX), The Open Group Base Specifications Issue 6, Copyright (C) 2001-2003 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 orig-
inal Standard can be obtained online at http://www.opengroup.org/unix/online.html .
IEEE/The Open Group 2003 WHO(P)