This function allows a process to attempt to change its effective group ID to that specified by gid . Unpriviledged users (for instance, the web server process on most systems) may only change the effective group ID to the real group ID and vice versa; other changes require super-user priviledges.
This is not actually a POSIX function and may not be supported on all systems. On unsupported systems, FALSE will always be returned. It should be supported on most BSD and SysV style systems, such as Linux and FreeBSD.
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