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 er-

       EPERM  The process group ID of any process equals the PID of the  call-
              ing 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 ses-
       sion 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 ses-
       sion 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 control-
       ling terminal.

       setsid(1),  getsid(2),  setpgid(2),  setpgrp(2),  tcgetsid(3),  creden-
       tials(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)
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