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().
