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

       setsid - creates a session and sets the process group ID

       #include <unistd.h>

       pid_t setsid(void);

       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

       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).

       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 error.

       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.

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

       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

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

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       latest version of this page, can be found at

Linux                              2021-03-22                          SETSID(2)