create session and set process group
setsid function creates a new session.
The calling process is the session leader of the new session, is the process
group leader of a new process group and has no controlling terminal. The
calling process is the only process in either the session or the process
Upon successful completion, the
function returns the value of the process group ID of the new process group,
which is the same as the process ID of the calling process.
If an error occurs,
setsid returns -1 and
the global variable errno is set to indicate the
error, as follows:
- The calling process is already a process group leader, or the process group ID of a process other than the calling process matches the process ID of the calling process.
getsid(2), setpgid(2), tcgetpgrp(3), tcsetpgrp(3)
setsid function is expected to be
compliant with the IEEE Std 1003.1-2008