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

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

SYNOPSIS
       #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 ||
           _XOPEN_SOURCE && _XOPEN_SOURCE_EXTENDED

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

ERRORS
       EPERM  The calling process is not privileged (Linux: does not have  the
              CAP_SETUID capability in the case of setreuid(), or the CAP_SET-
              GID 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.

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

NOTES
       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 imple-
       mentations.

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

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

COLOPHON
       This  page  is  part of release 3.27 of the Linux man-pages project.  A
       description of the project, and information about reporting  bugs,  can
       be found at http://www.kernel.org/doc/man-pages/.

Linux                             2010-09-20                       SETREUID(2)

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