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 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         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 4.08 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)