man-pages/man2/setreuid.2

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.\"     @(#)setregid.2	6.4 (Berkeley) 3/10/91
.\"
.\" Modified Sat Jul 24 09:08:49 1993 by Rik Faith <faith@cs.unc.edu>
.\" Portions extracted from linux/kernel/sys.c:
.\"             Copyright (C) 1991, 1992  Linus Torvalds
.\"             May be distributed under the GNU General Public License
.\" Changes: 1994-07-29 by Wilf <G.Wilford@ee.surrey.ac.uk>
.\"          1994-08-02 by Wilf due to change in kernel.
.\"          2004-07-04 by aeb
.\"          2004-05-27 by Michael Kerrisk
.\"
.TH SETREUID 2 2007-07-26 "Linux" "Linux Programmer's Manual"
.SH NAME
setreuid, setregid \- set real and/or effective user or group ID
.SH SYNOPSIS
.B #include <sys/types.h>
.br
.B #include <unistd.h>
.sp
.BI "int setreuid(uid_t " ruid ", uid_t " euid );
.br
.BI "int setregid(gid_t " rgid ", gid_t " egid );
.sp
.in -4n
Feature Test Macro Requirements for glibc (see
.BR feature_test_macros (7)):
.in
.sp
.BR setreuid (),
.BR setregid ():
_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
.SH DESCRIPTION
.BR setreuid ()
sets real and effective user IDs of the calling process.

Supplying a value of \-1 for either the real or effective user ID forces
the system to leave that ID unchanged.

Unprivileged processes may only set the effective user ID to the real user ID,
the effective user ID or the saved set-user-ID.

POSIX: It is unspecified whether unprivileged processes may set the
real user ID to the real user ID, the effective user ID or the
saved set-user-ID.

Linux: Unprivileged users may only set the real user ID to
the real user ID or the effective user ID.

Linux: If the real user ID is set or the effective user ID is set to a value
not equal to the previous real user ID,
the saved set-user-ID will be set to the new effective user ID.

Completely analogously,
.BR setregid ()
sets real and effective group ID's of the calling process,
and all of the above holds with "group" instead of "user".
.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
(Linux: does not have the
.B CAP_SETUID
capability in the case of
.BR setreuid (),
or the
.B CAP_SETGID
capability in the case of
.BR setregid ())
and a change other than (i)
swapping the effective user (group) ID with the real user (group) ID,
or (ii) setting one to the value of the other or (iii) setting the
effective user (group) ID to the value of the
saved set-user-ID (saved set-group-ID) was specified.
.SH "CONFORMING TO"
POSIX.1-2001, 4.3BSD (the
.BR setreuid ()
and
.BR setregid ()
function calls first appeared in 4.2BSD).
.SH NOTES
Setting the effective user (group) ID to the
saved set-user-ID (saved set-group-ID) is
possible since Linux 1.1.37 (1.1.38).
.SH "SEE ALSO"
.BR getgid (2),
.BR getuid (2),
.BR seteuid (2),
.BR setgid (2),
.BR setresuid (2),
.BR setuid (2),
.BR capabilities (7)