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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  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
       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
       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 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.

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

COLOPHON
       This  page  is  part of release 3.55 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					    2013-12-12				      SETREUID(2)
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