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

NAME         top

       setreuid, setregid - set real and/or effective user or group ID

SYNOPSIS         top

       #include <sys/types.h>
       #include <unistd.h>

       int setreuid(uid_t ruid, uid_t euid);
       int setregid(gid_t rgid, gid_t egid);

   Feature Test Macro Requirements for glibc (see feature_test_macros(7)):

       setreuid(), setregid():
           _BSD_SOURCE || _XOPEN_SOURCE >= 500 ||

DESCRIPTION         top

       setreuid() sets real and effective user IDs of the calling process.

       Supplying a value of -1 for either the real or effective user ID
       forces the system to leave that ID unchanged.

       Unprivileged processes may only set the effective user ID to the real
       user ID, the effective user ID, or the saved set-user-ID.

       Unprivileged users may only set the real user ID to the real user ID
       or the effective user ID.

       If the real user ID is set (i.e., ruid is not -1) or the effective
       user ID is set to a value not equal to the previous real user ID, the
       saved set-user-ID will be set to the new effective user ID.

       Completely analogously, setregid() sets real and effective group ID's
       of the calling process, and all of the above holds with "group"
       instead of "user".

RETURN VALUE         top

       On success, zero is returned.  On error, -1 is returned, and errno is
       set appropriately.

       Note: there are cases where setreuid() can fail even when the caller
       is UID 0; it is a grave security error to omit checking for a failure
       return from setreuid().

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 (Linux: does not have
              the CAP_SETUID capability in the case of setreuid(), or the
              CAP_SETGID capability in the case of setregid()) and a change
              other than (i) swapping the effective user (group) ID with the
              real user (group) ID, or (ii) setting one to the value of the
              other or (iii) setting the effective user (group) ID to the
              value of the saved set-user-ID (saved set-group-ID) was

CONFORMING TO         top

       POSIX.1-2001, 4.3BSD (the setreuid() and setregid() function calls
       first appeared in 4.2BSD).

NOTES         top

       Setting the effective user (group) ID to the saved set-user-ID (saved
       set-group-ID) is possible since Linux 1.1.37 (1.1.38).

       POSIX.1 does not specify all of possible ID changes that are
       permitted on Linux for an unprivileged process.  For setreuid(), the
       effective user ID can be made the same as the real user ID or the
       save set-user-ID, and it is unspecified whether unprivileged
       processes may set the real user ID to the real user ID, the effective
       user ID, or the saved set-user-ID.  For setregid(), the real group ID
       can be changed to the value of the saved set-group-ID, and the
       effective group ID can be changed to the value of the real group ID
       or the saved set-group-ID.  The precise details of what ID changes
       are permitted vary across implementations.

       POSIX.1 makes no specification about the effect of these calls on the
       saved set-user-ID and saved set-group-ID.

       The original Linux setreuid() and setregid() system calls supported
       only 16-bit user and group IDs.  Subsequently, Linux 2.4 added
       setreuid32() and setregid32(), supporting 32-bit IDs.  The glibc
       setreuid() and setregid() wrapper functions transparently deal with
       the variations across kernel versions.

SEE ALSO         top

       getgid(2), getuid(2), seteuid(2), setgid(2), setresuid(2), setuid(2),
       capabilities(7), user_namespaces(7)

COLOPHON         top

       This page is part of release 3.80 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

Linux                            2014-09-21                      SETREUID(2)