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.

NAME

       setsid — create session and set process group ID

SYNOPSIS

       #include <unistd.h>

       pid_t setsid(void);

DESCRIPTION

       The  setsid() function shall create a new session, if the calling process is not a process
       group leader. Upon return the calling process shall be the  session  leader  of  this  new
       session,  shall  be  the  process  group  leader of a new process group, and shall have no
       controlling terminal. The process group ID of the calling process shall be  set  equal  to
       the  process  ID  of the calling process. The calling process shall be the only process in
       the new process group and the only process in the new session.

RETURN VALUE

       Upon successful completion, setsid() shall return the value of the new process group ID of
       the calling process. Otherwise, it shall return -1 and set errno to indicate the error.

ERRORS

       The setsid() function shall fail if:

       EPERM  The calling process is already a process group leader, or the process group ID of a
              process other than the calling process  matches  the  process  ID  of  the  calling
              process.

       The following sections are informative.

EXAMPLES

       None.

APPLICATION USAGE

       None.

RATIONALE

       The setsid() function is similar to the setpgrp() function of System V.  System V, without
       job control, groups processes into process groups  and  creates  new  process  groups  via
       setpgrp(); only one process group may be part of a login session.

       Job  control  allows multiple process groups within a login session. In order to limit job
       control actions so that they can only affect processes in the  same  login  session,  this
       volume  of  POSIX.1‐2017  adds the concept of a session that is created via setsid().  The
       setsid() function also creates  the  initial  process  group  contained  in  the  session.
       Additional  process  groups  can be created via the setpgid() function. A System V process
       group would correspond to a POSIX System Interfaces  session  containing  a  single  POSIX
       process  group. Note that this function requires that the calling process not be a process
       group leader. The usual way to ensure this is true is to create a new process with  fork()
       and  have it call setsid().  The fork() function guarantees that the process ID of the new
       process does not match any existing process group ID.

FUTURE DIRECTIONS

       None.

SEE ALSO

       getsid(), setpgid(), setpgrp()

       The Base Definitions volume of POSIX.1‐2017, <sys_types.h>, <unistd.h>

COPYRIGHT

       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 .