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
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.
On success, the (new) session ID of the calling process is returned.
is returned, and
is set to indicate the error.
The process group ID of any process equals the PID of the calling process.
Thus, in particular,
fails if the calling process is already a process group leader.
A child created via
inherits its parent's session ID.
The session ID is preserved across an
A process group leader is a process with process group ID equal
to its PID.
In order to be sure that
and have the child do