.\" Copyright (C), 1994, Graeme W. Wilford (Wilf).
.\"
+.\" %%%LICENSE_START(VERBATIM)
.\" Permission is granted to make and distribute verbatim copies of this
.\" manual provided the copyright notice and this permission notice are
.\" preserved on all copies.
.\"
.\" Formatted or processed versions of this manual, if unaccompanied by
.\" the source, must acknowledge the copyright and authors of this work.
+.\" %%%LICENSE_END
.\"
.\" Fri Jul 29th 12:56:44 BST 1994 Wilf. <G.Wilford@ee.surrey.ac.uk>
.\" Changes inspired by patch from Richard Kettlewell
.\" <richard@greenend.org.uk>, aeb 970616.
.\" Modified, 27 May 2004, Michael Kerrisk <mtk.manpages@gmail.com>
.\" Added notes on capability requirements
-.TH SETUID 2 2010-02-21 "Linux" "Linux Programmer's Manual"
+.TH SETUID 2 2014-09-21 "Linux" "Linux Programmer's Manual"
.SH NAME
setuid \- set user identity
.SH SYNOPSIS
.BR setuid ().
You can accomplish this with
.BR seteuid (2).
-.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 setuid ()
+can fail even when the caller is UID 0;
+it is a grave security error to omit checking for a failure return from
+.BR setuid ().
.SH ERRORS
.TP
.B EAGAIN
-The
+The call would change the caller's real UID (i.e.,
+.I uid
+does not match the caller's real UID),
+but there was a temporary failure allocating the
+necessary kernel data structures.
+.TP
+.B EAGAIN
.I uid
-does not match the current uid and
+does not match the real user ID of the caller and this call would
+bring the number of processes belonging to the real user ID
.I uid
-brings process over its
+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
+The user ID specified in
+.I uid
+is not valid in this user namespace.
.TP
.B EPERM
The user is not privileged (Linux: does not have the
capability) and
.I uid
does not match the real UID or saved set-user-ID of the calling process.
-.SH "CONFORMING TO"
+.SH CONFORMING TO
SVr4, POSIX.1-2001.
Not quite compatible with the 4.4BSD call, which
sets all of the real, saved, and effective user IDs.
.\" SVr4 documents an additional EINVAL error condition.
.SH NOTES
-.SS Linux Notes
-Linux has the concept of file system user ID, normally equal to the
+Linux has the concept of the filesystem user ID, normally equal to the
effective user ID.
The
.BR setuid ()
-call also sets the file system user ID of the calling process.
+call also sets the filesystem user ID of the calling process.
See
.BR setfsuid (2).
.PP
If
.I uid
-is different from the old effective uid, the process will
+is different from the old effective UID, the process will
be forbidden from leaving core dumps.
-.SH "SEE ALSO"
+
+The original Linux
+.BR setuid ()
+system call supported only 16-bit user IDs.
+Subsequently, Linux 2.4 added
+.BR setuid32 ()
+supporting 32-bit IDs.
+The glibc
+.BR setuid ()
+wrapper function transparently deals with the variation across kernel versions.
+.SH SEE ALSO
.BR getuid (2),
.BR seteuid (2),
.BR setfsuid (2),
.BR setreuid (2),
.BR capabilities (7),
-.BR credentials (7)
+.BR credentials (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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