NAME

       setsid - creates a session and sets the process group ID

LIBRARY

       Standard C library (libc, -lc)

SYNOPSIS

       #include <unistd.h>

       pid_t setsid(void);

DESCRIPTION

       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

       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.

ERRORS

       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.

STANDARDS

       POSIX.1-2008.

HISTORY

       POSIX.1-2001, SVr4.

NOTES

       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

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