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getgid, getegid — get group process identification
Standard C Library (libc, -lc)
The getgid() system call 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-user-id of the calling process.
The getgid() and getegid() system calls are always successful, and no
return value is reserved to indicate an error.
getuid(2), issetugid(2), setgid(2), setregid(2)
The getgid() and getegid() system calls are expected to conform to
ISO/IEC 9945-1:1990 (“POSIX.1”).