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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON |
SETRESUID(2) Linux Programmer's Manual SETRESUID(2)
setresuid, setresgid - set real, effective and saved user or group ID
#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);
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.
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().
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.
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
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).
getresuid(2), getuid(2), setfsgid(2), setfsuid(2), setreuid(2),
setuid(2), capabilities(7), credentials(7), user_namespaces(7)
This page is part of release 4.12 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/.
Linux 2016-10-08 SETRESUID(2)
Pages that refer to this page: execve(2), getresuid(2), seteuid(2), setreuid(2), syscalls(2), capabilities(7), credentials(7), nptl(7), user_namespaces(7)