setresuid32(2)
NAME
setresuid, setresgid - set real, effective and saved user or group ID
SYNOPSIS
#define _GNU_SOURCE /* See feature_test_macros(7) */
#include <unistd.h>
int setresuid(uid_t ruid, uid_t euid, uid_t suid);
int setresgid(gid_t rgid, gid_t egid, gid_t sgid);
DESCRIPTION
setresuid() sets the real user ID, the effective user ID, and the saved
set-user-ID of the calling process.
An unprivileged process may change its real UID, effective UID, and
saved set-user-ID, each to one of: the current real UID, the current
effective UID or the current saved set-user-ID.
A privileged process (on Linux, one having the CAP_SETUID capability)
may set its real UID, effective UID, and saved set-user-ID to arbitrary
values.
If one of the arguments equals -1, the corresponding value is not
changed.
Regardless of what changes are made to the real UID, effective UID, and
saved set-user-ID, the filesystem UID is always set to the same value
as the (possibly new) effective UID.
Completely analogously, setresgid() sets the real GID, effective GID,
and saved set-group-ID of the calling process (and always modifies the
filesystem GID to be the same as the effective GID), with the same
restrictions for unprivileged processes.
RETURN VALUE
On success, zero is returned. On error, -1 is returned, and errno is
set appropriately.
Note: there are cases where setresuid() can fail even when the caller
is UID 0; it is a grave security error to omit checking for a failure
return from setresuid().
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).
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 (did not have the
necessary capability in its user namespace) and tried to change
the IDs to values that are not permitted. For setresuid(), the
necessary capability is CAP_SETUID; for setresgid(), it is
CAP_SETGID.
VERSIONS
These calls are available under Linux since Linux 2.1.44.
CONFORMING TO
These calls are nonstandard; they also appear on HP-UX and some of the
BSDs.
NOTES
Under HP-UX and FreeBSD, the prototype is found in <unistd.h>. Under
Linux, the prototype is provided by glibc since version 2.3.2.
The original Linux setresuid() and setresgid() system calls supported
only 16-bit user and group IDs. Subsequently, Linux 2.4 added
setresuid32() and setresgid32(), supporting 32-bit IDs. The glibc
setresuid() and setresgid() 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 setresuid() and setresgid()) 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).
SEE ALSO
getresuid(2), getuid(2), setfsgid(2), setfsuid(2), setreuid(2),
setuid(2), capabilities(7), credentials(7), user_namespaces(7)
COLOPHON
This page is part of release 4.09 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
https://www.kernel.org/doc/man-pages/.
Free and Open Source Software