+++ /dev/null
-.\" 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.
-.\"
-.\" Permission is granted to copy and distribute modified versions of this
-.\" manual under the conditions for verbatim copying, provided that the
-.\" entire resulting derived work is distributed under the terms of a
-.\" permission notice identical to this one.
-.\"
-.\" Since the Linux kernel and libraries are constantly changing, this
-.\" manual page may be incorrect or out-of-date. The author(s) assume no
-.\" responsibility for errors or omissions, or for damages resulting from
-.\" the use of the information contained herein. The author(s) may not
-.\" have taken the same level of care in the production of this manual,
-.\" which is licensed free of charge, as they might when working
-.\" professionally.
-.\"
-.\" 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 2014-09-21 "Linux" "Linux Programmer's Manual"
-.SH NAME
-setuid \- set user identity
-.SH SYNOPSIS
-.B #include <sys/types.h>
-.br
-.B #include <unistd.h>
-.sp
-.BI "int setuid(uid_t " uid );
-.SH DESCRIPTION
-.BR setuid ()
-sets the effective user ID of the calling process.
-If the effective UID of the caller is root,
-the real UID and saved set-user-ID are also set.
-.PP
-Under Linux,
-.BR setuid ()
-is implemented like the POSIX version with the
-.B _POSIX_SAVED_IDS
-feature.
-This allows a set-user-ID (other than root) program to drop all of its user
-privileges, do some un-privileged work, and then reengage the original
-effective user ID in a secure manner.
-.PP
-If the user is root or the program is set-user-ID-root, special care must be
-taken.
-The
-.BR setuid ()
-function checks the effective user ID of the caller and if it is
-the superuser, all process-related user ID's are set to
-.IR uid .
-After this has occurred, it is impossible for the program to regain root
-privileges.
-.PP
-Thus, a set-user-ID-root program wishing to temporarily drop root
-privileges, assume the identity of an unprivileged user, and then regain
-root privileges afterward cannot use
-.BR setuid ().
-You can accomplish this with
-.BR seteuid (2).
-.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 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 real user ID of the caller and this call would
-bring the number of processes belonging to the real user ID
-.I uid
-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
-.B CAP_SETUID
-capability) and
-.I uid
-does not match the real UID or saved set-user-ID of the calling process.
-.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
-Linux has the concept of the filesystem user ID, normally equal to the
-effective user ID.
-The
-.BR setuid ()
-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
-be forbidden from leaving core dumps.
-
-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 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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