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
IEEE Std 1003.1-2001, 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.
Process the implementation-defined database or named file
with the -b, -d, -l, -p, -r, -t,
-T and -u options turned on.
Write the time and date of the last reboot.
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
Write column headings above the regular output.
(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.
Output only information about the current terminal.
List any other process that is currently active and has
been previously spawned by init.
(Quick.) List only the names and the number of users
currently logged on. When this option is used, all other options shall be
Write the current run-level of the init
List only the <name>, <line>, and
< time> fields. This is the default case.
Indicate the last change to the system clock.
Show the state of each terminal, as described in the STDOUT
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 environment variables shall affect the execution of who:
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, Internationalization
Variables for the precedence of internationalization variables used to
determine the values of locale categories.)
If set to a non-empty string value, override the values of
all the other internationalization variables.
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).
Determine the locale that should be used to affect the
format and contents of diagnostic 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.
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 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:
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.
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 Extension. 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
It is acceptable for an implementation to produce no output for an invocation of
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 original
Standard can be obtained online at http://www.opengroup.org/unix/online.html