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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | STANDARDS | HISTORY | SEE ALSO | COLOPHON |
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setreuid(2) System Calls Manual setreuid(2)
setreuid, setregid - set real and/or effective user or group ID
Standard C library (libc, -lc)
#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():
_XOPEN_SOURCE >= 500
|| /* Since glibc 2.19: */ _DEFAULT_SOURCE
|| /* glibc <= 2.19: */ _BSD_SOURCE
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".
On success, zero is returned. On error, -1 is returned, and errno
is set to indicate the error.
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().
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).
EINVAL One or more of the target user or group IDs is not valid in
this user namespace.
EPERM The calling process is not privileged (on Linux, does not
have the necessary capability in its user namespace:
CAP_SETUID in the case of setreuid(), or CAP_SETGID 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 does not specify all of the UID changes that Linux permits
for an unprivileged process. For setreuid(), the effective user
ID can be made the same as the real user ID or the saved 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.
POSIX.1-2008.
POSIX.1-2001, 4.3BSD (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).
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.
C library/kernel differences
At the kernel level, user IDs and group IDs are a per-thread
attribute. However, POSIX requires that all threads in a process
share the same credentials. The NPTL threading implementation
handles the POSIX requirements by providing wrapper functions for
the various system calls that change process UIDs and GIDs. These
wrapper functions (including those for setreuid() and setregid())
employ a signal-based technique to ensure that when one thread
changes credentials, all of the other threads in the process also
change their credentials. For details, see nptl(7).
getgid(2), getuid(2), seteuid(2), setgid(2), setresuid(2),
setuid(2), capabilities(7), credentials(7), user_namespaces(7)
This page is part of the man-pages (Linux kernel and C library
user-space interface documentation) project. Information about
the project can be found at
⟨https://www.kernel.org/doc/man-pages/⟩. If you have a bug report
for this manual page, see
⟨https://git.kernel.org/pub/scm/docs/man-pages/man-pages.git/tree/CONTRIBUTING⟩.
This page was obtained from the tarball man-pages-6.10.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2025-02-02. If you discover any rendering problems in this HTML
version of the page, or you believe there is a better or more up-
to-date source for the page, or you have corrections or
improvements to the information in this COLOPHON (which is not
part of the original manual page), send a mail to
man-pages@man7.org
Linux man-pages 6.10 2024-07-23 setreuid(2)
Pages that refer to this page: execve(2), getgid(2), getresuid(2), getuid(2), seteuid(2), setgid(2), setresuid(2), setuid(2), syscalls(2), capabilities(7), credentials(7), nptl(7), user_namespaces(7)
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HTML rendering created 2025-02-02 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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