create session and set process group
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 group.
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