setsid - creates a session and sets the process group ID
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.
The session ID of the calling process.
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.
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().
Linux 1.0.0 1994-08-27 SETSID(2)
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