setresuid(2) — Linux manual page

NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | ERRORS | VERSIONS | CONFORMING TO | NOTES | SEE ALSO | COLOPHON

SETRESUID(2)            Linux Programmer's Manual           SETRESUID(2)

NAME         top

       setresuid, setresgid - set real, effective, and saved user or
       group ID

SYNOPSIS         top

       #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         top

       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         top

       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().

ERRORS         top

       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         top

       These calls are available under Linux since Linux 2.1.44.

CONFORMING TO         top

       These calls are nonstandard; they also appear on HP-UX and some
       of the BSDs.

NOTES         top

       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         top

       getresuid(2), getuid(2), setfsgid(2), setfsuid(2), setreuid(2),
       setuid(2), capabilities(7), credentials(7), user_namespaces(7)

COLOPHON         top

       This page is part of release 5.11 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                          2021-03-22                   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)