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       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.


       who — display who is on the system


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

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

       who -q [file]

       who am i

       who am I


       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  POSIX.1‐2017,  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 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

       -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.


       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.


       Not used.




       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,   Section   8.2,
                 Internationalization   Variables  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

                 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

       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.




       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:


       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>, <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.


       The standard error shall be used only for diagnostic messages.






       The following exit values shall be returned:

        0    Successful completion.

       >0    An error occurred.



       The following sections are informative.


       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

       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 who mil.





       The  Base  Definitions  volume  of POSIX.1‐2017, Chapter 8, Environment Variables, Section
       12.2, Utility Syntax Guidelines


       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 .

       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 .