getpgid - get process group ID

Syntax	#include <unistd.h> pid_t getpgid(pid_t pid);
Description	getpgid() returns the process group ID of the process whose process ID is pid. If pid is 0, the process group ID of the calling process is returned.
Return val.	Process group ID
		if successful.
	(pid_t)-1	if an error occurs. errno is set to indicate the error.
Errors	getpgid() will fail if:
	EPERM	The process whose process ID is pid is not in the same session as the calling process, and the implementation does not allow access to the process group ID of this process from within the calling process.
	ESRCH	There is no process with a process ID pid.
	EINVAL	The value of pid is invalid.
See also	exec, fork(), getpgrp(), getpid(), getsid(), setpgid(), setsid(), unistd.h.