.\" Copyright (c) 1983, 1991 The Regents of the University of California.
.\" All rights reserved.
.\"
+.\" %%%LICENSE_START(BSD_4_CLAUSE_UCB)
.\" Redistribution and use in source and binary forms, with or without
.\" modification, are permitted provided that the following conditions
.\" are met:
.\" LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING IN ANY WAY
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.\"
.\" @(#)setregid.2 6.4 (Berkeley) 3/10/91
.\"
.\" 2004-07-04 by aeb
.\" 2004-05-27 by Michael Kerrisk
.\"
-.TH SETREUID 2 2009-10-17 "Linux" "Linux Programmer's Manual"
+.TH SETREUID 2 2014-09-21 "Linux" "Linux Programmer's Manual"
.SH NAME
setreuid, setregid \- set real and/or effective user or group ID
.SH SYNOPSIS
.sp
.BR setreuid (),
.BR setregid ():
-_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500
+.RS 4
+.ad l
+_BSD_SOURCE || _XOPEN_SOURCE\ >=\ 500 ||
+_XOPEN_SOURCE\ &&\ _XOPEN_SOURCE_EXTENDED
+.ad
+.RE
.SH DESCRIPTION
.BR setreuid ()
sets real and effective user IDs of the calling process.
Unprivileged users may only set the real user ID to
the real user ID or the effective user ID.
-If the real user ID is set or the effective user ID is set to a value
+If the real user ID is set (i.e.,
+.I ruid
+is not \-1) 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.
.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"
+.SH RETURN VALUE
On success, zero is returned.
On error, \-1 is returned, and
.I errno
is set appropriately.
+
+.IR Note :
+there are cases where
+.BR setreuid ()
+can fail even when the caller is UID 0;
+it is a grave security error to omit checking for a failure return from
+.BR setreuid ().
.SH ERRORS
.TP
+.B EAGAIN
+The call would change the caller's real UID (i.e.,
+.I ruid
+does not match the caller's real UID),
+but there was a temporary failure allocating the
+necessary kernel data structures.
+.TP
+.B EAGAIN
+.I ruid
+does not match the caller's real UID and this call would
+bring the number of processes belonging to the real user ID
+.I ruid
+over the caller's
+.B RLIMIT_NPROC
+resource limit.
+Since Linux 3.1, this error case no longer occurs
+(but robust applications should check for this error);
+see the description of
+.B EAGAIN
+in
+.BR execve (2).
+.TP
+.B EINVAL
+One or more of the target user or group IDs
+is not valid in this user namespace.
+.TP
.B EPERM
The calling process is not privileged
(Linux: does not have the
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"
+.SH CONFORMING TO
POSIX.1-2001, 4.3BSD (the
.BR setreuid ()
and
POSIX.1 makes no specification about the effect of these calls
on the saved set-user-ID and saved set-group-ID.
-.SH "SEE ALSO"
+
+The original Linux
+.BR setreuid ()
+and
+.BR setregid ()
+system calls supported only 16-bit user and group IDs.
+Subsequently, Linux 2.4 added
+.BR setreuid32 ()
+and
+.BR setregid32 (),
+supporting 32-bit IDs.
+The glibc
+.BR setreuid ()
+and
+.BR setregid ()
+wrapper functions transparently deal with the variations across kernel versions.
+.SH SEE ALSO
.BR getgid (2),
.BR getuid (2),
.BR seteuid (2),
.BR setgid (2),
.BR setresuid (2),
.BR setuid (2),
-.BR capabilities (7)
+.BR capabilities (7),
+.BR user_namespaces (7)
+.SH COLOPHON
+This page is part of release 3.79 of the Linux
+.I man-pages
+project.
+A description of the project,
+information about reporting bugs,
+and the latest version of this page,
+can be found at
+\%http://www.kernel.org/doc/man\-pages/.
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