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

       setsid - creates a session and sets the process group ID

       #include <sys/types.h>
       #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

       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

       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.

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

       This page is part of release 5.05 of the Linux man-pages project.  A
       description of the project, information about reporting bugs, and the
       latest version of this page, can be found at

Linux                             2017-09-15                         SETSID(2)