The
getgid() function returns the real group ID of the calling process,
getegid() returns the effective group ID of the calling process.
The real group ID is specified at login time.
The real group ID is the group of the user who invoked the program. As the effective group ID gives the process additional permissions during the execution of “
set-group-ID” mode processes,
getgid() is used to determine the real-group-id of the calling process.