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SETREUID(2) Linux Programmer's Manual SETREUID(2)
setreuid, setregid - set real and/or effective user or group ID
#include <sys/types.h>
#include <unistd.h>
int setreuid(uid_t ruid, uid_t euid);
int setregid(gid_t rgid, gid_t egid);
Feature Test Macro Requirements for glibc (see feature_test_macros(7)):
setreuid(), setregid():
_BSD_SOURCE || _XOPEN_SOURCE >= 500 ||
_XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED
setreuid() sets real and effective user IDs of the calling process.
Supplying a value of -1 for either the real or effective user ID forces the
system to leave that ID unchanged.
Unprivileged processes may only set the effective user ID to the real user ID,
the effective user ID, or the saved set-user-ID.
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 not
equal to the previous real user ID, the saved set-user-ID will be set to the
new effective user ID.
Completely analogously, setregid() sets real and effective group ID's of the
calling process, and all of the above holds with "group" instead of "user".
On success, zero is returned. On error, -1 is returned, and errno is set
appropriately.
EPERM The calling process is not privileged (Linux: does not have the
CAP_SETUID capability in the case of setreuid(), or the CAP_SETGID
capability in the case of setregid()) and a change other than (i)
swapping the effective user (group) ID with the real user (group) ID,
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.
POSIX.1-2001, 4.3BSD (the setreuid() and setregid() function calls first
appeared in 4.2BSD).
Setting the effective user (group) ID to the saved set-user-ID (saved set-
group-ID) is possible since Linux 1.1.37 (1.1.38).
POSIX.1 does not specify all of possible ID changes that are permitted on
Linux for an unprivileged process. For setreuid(), the effective user ID can
be made the same as the real user ID or the save set-user-ID, and it is
unspecified whether unprivileged processes may set the real user ID to the
real user ID, the effective user ID, or the saved set-user-ID. For
setregid(), the real group ID can be changed to the value of the saved set-
group-ID, and the effective group ID can be changed to the value of the real
group ID or the saved set-group-ID. The precise details of what ID changes
are permitted vary across implementations.
POSIX.1 makes no specification about the effect of these calls on the saved
set-user-ID and saved set-group-ID.
The original Linux setreuid() and setregid() system calls supported only
16-bit user and group IDs. Subsequently, Linux 2.4 added setreuid32() and
setregid32(), supporting 32-bit IDs. The glibc setreuid() and setregid()
wrapper functions transparently deal with the variations across kernel
versions.
getgid(2), getuid(2), seteuid(2), setgid(2), setresuid(2), setuid(2),
capabilities(7)
This page is part of release 3.32 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/.
Linux 2010-11-22 SETREUID(2)
HTML rendering created 2010-12-03 by Michael Kerrisk, author of The Linux Programming Interface