redhat man page for setsid

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

NAME
       setsid - creates a session and sets the process group ID

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,
       the process group leader of the new process group, and has no controlling tty.  The process group ID and session ID of the calling  process
       are set to the PID of the calling process.  The calling process will be the only process in this new process group and in this new session.

RETURN VALUE
       The session ID of the calling process.

ERRORS
       On  error,  -1  will be returned.  The only error which can happen is EPERM. It is returned when 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.

NOTES
       A process group leader is a process with process group ID equal to its PID. In order to be sure that setsid will succeed,  fork	and  exit,
       and have the child do setsid().

CONFORMING TO
       POSIX, SVr4.

SEE ALSO
       setpgid(2), setpgrp(2)

Linux 1.0.0							    1994-08-27								 SETSID(2)