Name
setuid — set user identity
DESCRIPTION
setuid() sets the effective
user ID of the current 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 re-engage 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 a non-root user,
and then regain root privileges afterwards cannot use
setuid(). You can accomplish
this with the (non-POSIX, BSD) call seteuid(2).
RETURN VALUE
On success, zero is returned. On error, −1 is
returned, and errno is set
appropriately.
ERRORS
- EAGAIN
-
The uid does
not match the current uid and uid brings process over
its NPROC rlimit.
- EPERM
-
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.
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.
NOTES
Linux Notes
Linux has the concept of filesystem user ID, normally
equal to the effective user ID. The setuid() call also sets the filesystem
user ID of the current process. See setfsuid(2).
If uid is
different from the old effective uid, the process will be
forbidden from leaving core dumps.
SEE ALSO
getuid(2), seteuid(2), setfsuid(2), setreuid(2), capabilities(7), credentials(7)
Copyright (C), 1994, Graeme W. Wilford (Wilf).
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manual page may be incorrect or out-of-date.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.
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@gmx.net>
Added notes on capability requirements
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