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

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_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.

SEE ALSO

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

COLOPHON

       This page is part of release 3.25 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								    2009-10-17							       SETREUID(2)