debian man page for setgid

SETGID(2)						     Linux Programmer's Manual							 SETGID(2)

NAME
       setgid - set group identity

SYNOPSIS
       #include <sys/types.h>
       #include <unistd.h>

       int setgid(gid_t gid);

DESCRIPTION
       setgid()  sets the effective group ID of the calling process.  If the caller is the superuser, the real GID and saved set-group-ID are also
       set.

       Under Linux, setgid() is implemented like the POSIX version with the _POSIX_SAVED_IDS feature.  This allows a set-group-ID program that	is
       not  set-user-ID-root to drop all of its group privileges, do some un-privileged work, and then reengage the original effective group ID in
       a secure manner.

RETURN VALUE
       On success, zero is returned.  On error, -1 is returned, and errno is set appropriately.

ERRORS
       EPERM  The calling process is not privileged (does not have the CAP_SETGID capability), and gid does not match the real group ID  or  saved
	      set-group-ID of the calling process.

NOTES
       The  original  Linux setgid() system call supported only 16-bit group IDs.  Subsequently, Linux 2.4 added setgid32() supporting 32-bit IDs.
       The glibc setgid() wrapper function transparently deals with the variation across kernel versions.

CONFORMING TO
       SVr4, POSIX.1-2001.

SEE ALSO
       getgid(2), setegid(2), setregid(2), capabilities(7), credentials(7)

COLOPHON
       This page is part of release 3.44 of the Linux man-pages project.  A description of the project, and information about reporting bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

Linux								    2010-11-22								 SETGID(2)