WHO(1P) POSIX Programmer's Manual WHO(1P)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.
NAMEwho — display who is on the system
SYNOPSISwho [−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 accessi‐
ble 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.1‐2008, 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 deter‐
mining 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 cur‐
rently 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 work‐
ing 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 implemen‐
tation-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 vari‐
ables that are unset or null. (See the Base Definitions vol‐
ume of POSIX.1‐2008, Section 8.2, Internationalization Vari‐
ables 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 infor‐
mation. If TZ is unset or null, an unspecified default time‐
zone 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 stan‐
dard 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 unspec‐
ified.
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. Addi‐
tional options to match historical systems are available on XSI-confor‐
mant 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 sup‐
porting 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.1‐2008, 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, 2013 Edition, Standard for Information Technology
-- Portable Operating System Interface (POSIX), The Open Group Base
Specifications Issue 7, Copyright (C) 2013 by the Institute of Electri‐
cal and Electronics Engineers, Inc and The Open Group. (This is
POSIX.1-2008 with the 2013 Technical Corrigendum 1 applied.) 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.unix.org/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.ker‐
nel.org/doc/man-pages/reporting_bugs.html .
IEEE/The Open Group 2013 WHO(1P)
