This manual page is part of the POSIX Programmer's Manual. The Linux implementation of this interface

       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.

       Default.

       Default.

       Thefollowingsectionsareinformative.

       Portions of this text are reprinted and reproduced in electronic form from IEEE Std 1003.1-2017, Standard
       for  Information  Technology  --  Portable  Operating  System  Interface  (POSIX),  The  Open  Group Base
       Specifications Issue 7, 2018 Edition, Copyright (C) 2018 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 .

       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.kernel.org/doc/man-pages/reporting_bugs.html .

IEEE/The Open Group                                   2017                                           WHO(1POSIX)

       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 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 POSIX.1‐2017, Section8.2, InternationalizationVariables 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 information. If TZ is unset or null,  an
                 unspecified default timezone shall be used.

       None.

       The following exit values shall be returned:

        0    Successful completion.

       >0    An error occurred.

       None.

       None.

       None.

       who — display who is on the system

       The following operands shall be supported:

       ami, amI
                 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 who utility shall conform to the Base Definitions  volume  of  POSIX.1‐2017,  Section12.2,  UtilitySyntaxGuidelines.

       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 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
                 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.

       None.

       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.

       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 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 whomil.

mesg

       The Base Definitions volume of POSIX.1‐2017, Chapter8,  EnvironmentVariables,  Section12.2,  UtilitySyntaxGuidelines

       The standard error shall be used only for diagnostic messages.

       Not 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:

           <name>[<state>]<line><time>[<activity>][<pid>][<comment>][<exit>]

       For the -b option, <line> shall be "systemboot".  The <name> is unspecified.

       The following format shall be used for the -T option:

           "%s %c %s %s\n" <name>, <terminalstate>, <terminalname>,
               <timeoflogin>

       where <terminalstate> 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 <timeoflogin> 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.

       who [-mTu][-abdHlprt][file]

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

       who -q [file]

       who am i

       who am I