getsid - get process group ID

Syntax	#include <unistd.h> pid_t getsid(pid_t pid);
Description	The getsid() function returns the process group ID of the process that is session leaderof the process with the ID pid. If pid is (pid_t)0, then getsid() returns the session number of the calling process.
Return val.	Process group ID
		if successful.
	(pid_t)-1	if an error occurs. errno is set to indicate the error.
Errors	getsid() will fail if:
	EPERM	The process with the process ID pid is not in the same session as the calling process, and the implementation does not support access by the calling process to the session number of the specified process.
	ESRCH	There is no process with the process ID pid.
See also	exec, fork(), getpid(), getpdig(), setpgid(), setsid(), unistd.h.