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 calling process is privileged (has the CAP_SETGID capability in its
       user namespace), 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

       EINVAL The group ID specified in gid is not valid in this user namespace.

       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.

CONFORMING TO

       POSIX.1-2001, POSIX.1-2008, SVr4.

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.

   C library/kernel differences
       At the kernel level, user IDs and group IDs are a per-thread attribute.	However, POSIX requires that all threads in a  process	share  the
       same  credentials.   The NPTL threading implementation handles the POSIX requirements by providing wrapper functions for the various system
       calls that change process UIDs and GIDs.  These wrapper functions (including the one for  setgid())  employ  a  signal-based  technique	to
       ensure  that  when one thread changes credentials, all of the other threads in the process also change their credentials.  For details, see
       nptl(7).

SEE ALSO

       getgid(2), setegid(2), setregid(2), capabilities(7), credentials(7), user_namespaces(7)

COLOPHON

       This page is part of release 4.15 of the Linux man-pages project.  A description of the project, information about reporting bugs, and  the
       latest version of this page, can be found at https://www.kernel.org/doc/man-pages/.

Linux								    2017-09-15								 SETGID(2)