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SETREUID(2) Linux Programmer's Manual SETREUID(2)
NAME
setreuid, setregid - set real and/or effective user or group ID
SYNOPSIS
#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
DESCRIPTION
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 (i.e., ruid is not -1) 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".
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is
set appropriately.
Note: there are cases where setreuid() can fail even when the caller is
UID 0; it is a grave security error to omit checking for a failure
return from setreuid().
ERRORS
EAGAIN The call would change the caller's real UID (i.e., ruid does not
match the caller's real UID), but there was a temporary failure
allocating the necessary kernel data structures.
EAGAIN ruid does not match the caller's real UID and this call would
bring the number of processes belonging to the real user ID ruid
over the caller's 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 EAGAIN in
execve(2).
EPERM The calling process is not privileged (Linux: does not have the
CAP_SETUID capability in the case of setreuid(), or the CAP_SET-
GID 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.
CONFORMING TO
POSIX.1-2001, 4.3BSD (the setreuid() and setregid() function calls
first appeared in 4.2BSD).
NOTES
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 imple-
mentations.
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.
SEE ALSO
getgid(2), getuid(2), seteuid(2), setgid(2), setresuid(2), setuid(2),
capabilities(7)
COLOPHON
This page is part of release 3.69 of the Linux 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/.
Linux 2014-06-13 SETREUID(2)
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