setgid - set group ID of process

Syntax	#include <unistd.h> Optional #include <sys/types.h> int setgid(gid_t gid);
Description	If the process has appropriate privileges, setgid() sets the real group ID, effective group ID, and the saved set-group-ID to gid. If the process does not have appropriate privileges, but gid is equal to the real group ID or the saved set-group-ID, setgid() sets the effective group ID to gid; the real group ID and saved set-group-ID remain unchanged. Any supplementary group IDs of the calling process remain unchanged.
Return val.	0 -1	if successful. if unsuccessful. errno is set to indicate the error.
Errors	setgid() will fail if:
	EINVAL	The value of gid is invalid and is not supported.
	EPERM	The process does not have appropriate privileges and gid does not match the real group ID or the saved set-group-ID.
Notes	At login, the real user ID, effective user ID, and saved set-user-ID of the login process are set to the user ID of the user responsible for creating the process. The real group ID, effective group ID, and saved set-group-ID of the login process are likewise set to the group ID of the user responsible for creating the process. When a process calls exec() to execute a file, the user and/or group IDs associated with the process may change. If the file executed is a 'set-user-ID' file, the effective user ID and saved set-user-ID of the process are set to the user of the file executed. If the file executed is a 'set-group-ID' file, the effective group ID and saved set-group-ID of the process are set to the group of the file executed. If the file executed is not a 'set-user-ID' or 'set-group-ID' file, the effective user ID, saved set-user-ID, effective group ID, and saved set-group-ID are not changed.
See also	exec, getgid(), setuid(), sys/types.h, unistd.h.