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setuid — set user identity
#include <sys/types.h> #include <unistd.h>
int
setuid( |
uid_t uid); |
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.
Under Linux, setuid() is
implemented like the POSIX version with the _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.
If the user is root or the program is set-user-ID-root,
special care must be taken. The 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 uid. After this has occurred,
it is impossible for the program to regain root
privileges.
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
setuid(). You can accomplish
this with seteuid(2).
On success, zero is returned. On error, −1 is
returned, and errno is set
appropriately.
The uid does
not match the current uid and uid brings process over
its RLIMIT_NPROC resource
limit.
The user is not privileged (Linux: does not have the
CAP_SETUID capability)
and uid does
not match the real UID or saved set-user-ID of the
calling process.
SVr4, POSIX.1-2001. Not quite compatible with the 4.4BSD call, which sets all of the real, saved, and effective user IDs.
Linux has the concept of the filesystem user ID, normally
equal to the effective user ID. The setuid() call also sets the filesystem user
ID of the calling process. See setfsuid(2).
If uid is
different from the old effective UID, the process will be
forbidden from leaving core dumps.
The original Linux setuid()
system call supported only 16-bit user IDs. Subsequently,
Linux 2.4 added setuid32()
supporting 32-bit IDs. The glibc setuid() wrapper function transparently
deals with the variation across kernel versions.
This page is part of release 3.54 of the Linux man-pages project. A
description of the project, and information about reporting
bugs, can be found at
http://www.kernel.org/doc/man−pages/.
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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.Wilfordee.surrey.ac.uk> Changes inspired by patch from Richard Kettlewell <richardgreenend.org.uk>, aeb 970616. Modified, 27 May 2004, Michael Kerrisk <mtk.manpagesgmail.com> Added notes on capability requirements |