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NAME | LIBRARY | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | STANDARDS | HISTORY | SEE ALSO | COLOPHON |
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setresuid(2) System Calls Manual setresuid(2)
setresuid, setresgid - set real, effective, and saved user or
group ID
Standard C library (libc, -lc)
#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 to indicate the error.
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.
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).
None.
Linux 2.1.44, glibc 2.3.2. HP-UX, FreeBSD.
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.
getresuid(2), getuid(2), setfsgid(2), setfsuid(2), setreuid(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-6.9.1.tar.gz
fetched from
⟨https://mirrors.edge.kernel.org/pub/linux/docs/man-pages/⟩ on
2024-06-26. 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 6.9.1 2024-05-02 setresuid(2)
Pages that refer to this page: execve(2), getresuid(2), seteuid(2), setreuid(2), syscalls(2), systemd.exec(5), capabilities(7), credentials(7), nptl(7), user_namespaces(7)
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HTML rendering created 2024-06-26 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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