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)

Linux man-pages 6.7                                2023-10-31                                          setsid(2)