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[thirdparty/man-pages.git] / man2 / setgid.2

.\" Copyright (C), 1994, Graeme W. Wilford. (Wilf.)
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.\" Fri Jul 29th 12:56:44 BST 1994  Wilf. <G.Wilford@ee.surrey.ac.uk>
.\" Modified 1997-01-31 by Eric S. Raymond <esr@thyrsus.com>
.\" Modified 2002-03-09 by aeb
.\"
.TH SETGID 2 2010-11-22 "Linux" "Linux Programmer's Manual"
.SH NAME
setgid \- set group identity
.SH SYNOPSIS
.B #include <sys/types.h>
.br
.B #include <unistd.h>
.sp
.BI "int setgid(gid_t " gid );
.SH DESCRIPTION
.BR 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,
.BR setgid ()
is implemented like the POSIX version with the
.B _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.
.SH RETURN VALUE
On success, zero is returned.
On error, \-1 is returned, and
.I errno
is set appropriately.
.SH ERRORS
.TP
.B EPERM
The calling process is not privileged (does not have the
\fBCAP_SETGID\fP capability), and
.I gid
does not match the real group ID or saved set-group-ID of
the calling process.
.SH CONFORMING TO
SVr4, POSIX.1-2001.
.SH NOTES
The original Linux
.BR setgid ()
system call supported only 16-bit group IDs.
Subsequently, Linux 2.4 added
.BR setgid32 ()
supporting 32-bit IDs.
The glibc
.BR setgid ()
wrapper function transparently deals with the variation across kernel versions.
.SH SEE ALSO
.BR getgid (2),
.BR setegid (2),
.BR setregid (2),
.BR capabilities (7),
.BR credentials (7)