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

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

       #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():

       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  effec‐
       tive 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

       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".

       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().

       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

       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

       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 capabil‐
              ity  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 specified.

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

       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

       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.

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

       This  page  is  part of release 3.74 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 http://www.kernel.org/doc/man-pages/.

Linux                                       2014-09-21                                SETREUID(2)

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