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 pro-
cess 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 ses-
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().