create session and set process group ID
() 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,
() 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.
() function is expected to be
compliant with the IEEE Std 1003.1-2008