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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 (con-
sult 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]

who [-mu]-s[-bHlprt][file]

who [-mTu][-abdHlprt][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 implemen-
tation-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 IEEE Std 1003.1-2001, Section 12.2, Utility Syntax Guide-
lines.

The following options shall be supported. The metavariables, such as <line>, refer to fields described in the STDOUT sec-
tion.

-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 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 termi-
nal 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 IEEE Std 1003.1-2001, Section 8.2, Internationalization Variables for the precedence of international-
ization 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 stan-
dard 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>]

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 for-
mat.

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 sys-
tems.

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 format.

It is acceptable for an implementation to produce no output for an invocation of who mil.

FUTURE DIRECTIONS
None.