SETSID(2)                 Linux Programmer's Manual                SETSID(2)

NAME         top

       setsid - creates a session and sets the process group ID

SYNOPSIS         top

       #include <unistd.h>

       pid_t setsid(void);

DESCRIPTION         top

       setsid() creates a new session if the calling process is not a
       process group leader.  The calling process is the leader of the new
       session (i.e., its session ID is made the same as its process ID).
       The calling process also becomes the process group leader of a new
       process group in the session (i.e., its process group ID is made the
       same as its process ID).

       The calling process will be the only process in the new process group
       and in the new session.

       Initially, the new session has no controlling terminal.  For details
       of how a session acquires a controlling terminal, see credentials(7).

RETURN VALUE         top

       On success, the (new) session ID of the calling process is returned.
       On error, (pid_t) -1 is returned, and errno is set to indicate the

ERRORS         top

       EPERM  The process group ID of any process equals the PID of the
              calling process.  Thus, in particular, setsid() fails if the
              calling process is already a process group leader.

CONFORMING TO         top

       POSIX.1-2001, POSIX.1-2008, SVr4.

NOTES         top

       A child created via fork(2) inherits its parent's session ID.  The
       session ID is preserved across an execve(2).

       A process group leader is a process whose process group ID equals its
       PID.  Disallowing a process group leader from calling setsid()
       prevents the possibility that a process group leader places itself in
       a new session while other processes in the process group remain in
       the original session; such a scenario would break the strict two-
       level hierarchy of sessions and process groups.  In order to be sure
       that setsid() will succeed, call fork(2) and have the parent
       _exit(2), while the child (which by definition can't be a process
       group leader) calls setsid().

       If a session has a controlling terminal, and the CLOCAL flag for that
       terminal is not set, and a terminal hangup occurs, then the session
       leader is sent a SIGHUP signal.

       If a process that is a session leader terminates, then a SIGHUP
       signal is sent to each process in the foreground process group of the
       controlling terminal.

SEE ALSO         top

       setsid(1), getsid(2), setpgid(2), setpgrp(2), tcgetsid(3),
       credentials(7), sched(7)

COLOPHON         top

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Linux                            2016-10-08                        SETSID(2)