setresuid, setresgid - set real, effective and saved user or group ID
/* See feature_test_macros(7) */
int setresuid(uid_t ruid, uid_t euid, uid_t
int setresgid(gid_t rgid, gid_t egid, gid_t
() 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
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
On success, zero is returned. On error, -1 is returned, and errno
: 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
- 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.
- 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
- One or more of the target user or group IDs is not valid in
this user namespace.
- 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
These calls are available under Linux since Linux 2.1.44.
These calls are nonstandard; they also appear on HP-UX and some of the BSDs.
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
() and setresgid32
(), supporting 32-bit IDs. The
() and setresgid
() wrapper functions
transparently deal with the variations across kernel versions.
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
()) 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)
This page is part of release 4.13 of the Linux man-pages
description of the project, information about reporting bugs, and the latest
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