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.TH WHO "1P" 2013 "IEEE/The Open Group" "POSIX Programmer's Manual"
.SH 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.

.SH NAME
who
\(em display who is on the system
.SH SYNOPSIS
.LP
.nf
who \fB[\fR\(mimTu\fB] [\fR\(miabdHlprt\fB] [\fIfile\fB]\fR
.P
who \fB[\fR\(mimu\fB] \fR\(mis\fB [\fR\(mibHlprt\fB] [\fIfile\fB]\fR
.P
who \(miq \fB[\fIfile\fB]\fR
.P
who am i
.P
who am I
.fi
.SH DESCRIPTION
The
.IR who
utility shall list various pieces of information about accessible
users. The domain of accessibility is implementation-defined.
.P
Based on the options given,
.IR 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.
.SH OPTIONS
The
.IR who
utility shall conform to the Base Definitions volume of POSIX.1\(hy2008,
.IR "Section 12.2" ", " "Utility Syntax Guidelines".
.P
The following options shall be supported. The metavariables, such as
<\fIline\fP>, refer to fields described in the STDOUT section.
.IP "\fB\(mia\fP" 10
Process the implementation-defined database or named file with the
.BR \(mib ,
.BR \(mid ,
.BR \(mil ,
.BR \(mip ,
.BR \(mir ,
.BR \(mit ,
.BR \(miT
and
.BR \(miu
options turned on.
.IP "\fB\(mib\fP" 10
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.
.IP "\fB\(mid\fP" 10
Write a list of all processes that have expired and not been respawned
by the
.IR init
system process. The <\fIexit\fP> 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.
.IP "\fB\(miH\fP" 10
Write column headings above the regular output.
.IP "\fB\(mil\fP" 10
(The letter ell.) List only those lines on which the system is waiting
for someone to login. The <\fIname\fP> field shall be
.BR LOGIN
in such cases. Other fields shall be the same as for user entries
except that the <\fIstate\fP> field does not exist.
.IP "\fB\(mim\fP" 10
Output only information about the current terminal.
.IP "\fB\(mip\fP" 10
List any other process that is currently active and has been previously
spawned by
.IR init .
.IP "\fB\(miq\fP" 10
(Quick.) List only the names and the number of users currently logged
on. When this option is used, all other options shall be ignored.
.IP "\fB\(mir\fP" 10
Write the current
.IR run-level
of the
.IR init
process.
.IP "\fB\(mis\fP" 10
List only the <\fIname\fR>, <\fIline\fR>, and <\fItime\fR> fields.
This is the default case.
.IP "\fB\(mit\fP" 10
Indicate the last change to the system clock.
.IP "\fB\(miT\fP" 10
Show the state of each terminal, as described in the STDOUT section.
.IP "\fB\(miu\fP" 10
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 <\fIname\fP> is the user's login name. The <\fIline\fP> is the name
of the line as found in the directory
.BR /dev .
The <\fItime\fP> is the time that the user logged in. The
<\fIactivity\fP> 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 <\fIold\fP>. This field is useful
when trying to determine whether a person is working at the terminal or
not. The <\fIpid\fP> is the process ID of the user's login process.
.SH OPERANDS
The following operands shall be supported:
.IP "\fBam\ i\fR,\ \fBam\ I\fR" 10
In the POSIX locale, limit the output to describing the invoking user,
equivalent to the
.BR \(mim
option. The
.BR am
and
.BR i
or
.BR I
must be separate arguments.
.IP "\fIfile\fR" 10
Specify a pathname of a file to substitute for the
implementation-defined database of logged-on users that
.IR who
uses by default.
.SH STDIN
Not used.
.SH "INPUT FILES"
None.
.SH "ENVIRONMENT VARIABLES"
The following environment variables shall affect the execution of
.IR who :
.IP "\fILANG\fP" 10
Provide a default value for the internationalization variables that are
unset or null. (See the Base Definitions volume of POSIX.1\(hy2008,
.IR "Section 8.2" ", " "Internationalization Variables"
for the precedence of internationalization variables used to determine
the values of locale categories.)
.IP "\fILC_ALL\fP" 10
If set to a non-empty string value, override the values of all the
other internationalization variables.
.IP "\fILC_CTYPE\fP" 10
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).
.IP "\fILC_MESSAGES\fP" 10
.br
Determine the locale that should be used to affect the format and
contents of diagnostic messages written to standard error.
.IP "\fILC_TIME\fP" 10
Determine the locale used for the format and contents of the date and
time strings.
.IP "\fINLSPATH\fP" 10
Determine the location of message catalogs for the processing of
.IR LC_MESSAGES .
.IP "\fITZ\fP" 10
Determine the timezone used when writing date and time information. If
.IR TZ
is unset or null, an unspecified default timezone shall be used.
.SH "ASYNCHRONOUS EVENTS"
Default.
.SH STDOUT
The
.IR 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.
.P
XSI-conformant systems shall write the default information to the
standard output in the following general format:
.sp
.RS 4
.nf
\fB
<\fIname\fR>\fB[\fR<\fIstate\fR>\fB]\fR<\fIline\fR><\fItime\fR>\fB[\fR<\fIactivity\fR>\fB][\fR<\fIpid\fR>\fB][\fR<\fIcomment\fR>\fB][\fR<\fIexit\fR>\fB]\fR
.fi \fR
.P
.RE
.P
For the
.BR \(mib
option, <\fIline\fP> shall be
.BR \(dqsystem boot\(dq .
The <\fIname\fP> is unspecified.
.P
The following format shall be used for the
.BR \(miT
option:
.sp
.RS 4
.nf
\fB
"%s %c %s %s\en" <\fIname\fR>, <\fIterminal state\fR>, <\fIterminal name\fR>,
    <\fItime of login\fR>
.fi \fR
.P
.RE
.P
where <\fIterminal\ state\fP> is one of the following characters:
.IP "\fR+\fR" 8
The terminal allows write access to other users.
.IP "\fR\(mi\fR" 8
The terminal denies write access to other users.
.IP "\fR?\fR" 8
The terminal write-access state cannot be determined.
.IP "\fR<space>\fR" 8
This entry is not associated with a terminal.
.P
In the POSIX locale, the <\fItime\ of\ login\fP> shall be equivalent in
format to the output of:
.sp
.RS 4
.nf
\fB
date +"%b %e %H:%M"
.fi \fR
.P
.RE
.P
If the
.BR \(miu
option is used with
.BR \(miT ,
the idle time shall be added to the end of the previous format in an
unspecified format.
.SH STDERR
The standard error shall be used only for diagnostic messages.
.SH "OUTPUT FILES"
None.
.SH "EXTENDED DESCRIPTION"
None.
.SH "EXIT STATUS"
The following exit values shall be returned:
.IP "\00" 6
Successful completion.
.IP >0 6
An error occurred.
.SH "CONSEQUENCES OF ERRORS"
Default.
.LP
.IR "The following sections are informative."
.SH "APPLICATION USAGE"
The name
.IR init
used for the system process is the most commonly used on historical
systems, but it may vary.
.P
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
.IR rwho .
.SH EXAMPLES
None.
.SH 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.
.P
It is recognized that the
.IR 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.
.P
No format was specified for the default
.IR 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.
.P
The format of the terminal name is unspecified, but the descriptions of
.IR ps ,
.IR talk ,
and
.IR write
require that they use the same format.
.P
It is acceptable for an implementation to produce no output for
an invocation of
.IR who
.BR mil .
.SH "FUTURE DIRECTIONS"
None.
.SH "SEE ALSO"
.IR "\fImesg\fR\^"
.P
The Base Definitions volume of POSIX.1\(hy2008,
.IR "Chapter 8" ", " "Environment Variables",
.IR "Section 12.2" ", " "Utility Syntax Guidelines"
.SH 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
Electrical 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 .

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