man7.org > Linux > man-pages

Linux/UNIX system programming training

setsid(3p) — Linux manual page

PROLOG | NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | EXAMPLES | APPLICATION USAGE | RATIONALE | FUTURE DIRECTIONS | SEE ALSO | COPYRIGHT 

SETSID(3P)              POSIX Programmer's Manual             SETSID(3P)

PROLOG         top

       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         top

       setsid — create session and set process group ID

SYNOPSIS         top

       #include <unistd.h>

       pid_t setsid(void);

DESCRIPTION         top

       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         top

       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         top

       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         top

       None.

APPLICATION USAGE         top

       None.

RATIONALE         top

       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         top

       None.

SEE ALSO         top

       getsid(3p), setpgid(3p), setpgrp(3p)

       The Base Definitions volume of POSIX.1‐2017, sys_types.h(0p),
       unistd.h(0p)

COPYRIGHT         top

       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                        SETSID(3P)

Pages that refer to this page: unistd.h(0p),  _Exit(3p),  getpgid(3p),  getpgrp(3p),  getpid(3p),  getppid(3p),  getsid(3p),  kill(3p),  setpgid(3p),  setpgrp(3p),  tcgetpgrp(3p)

HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface.

For details of in-depth Linux/UNIX system programming training courses that I teach, look here.

Hosting by jambit GmbH.

Cover of TLPI