MirBSD manpage: setreuid(2)

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


     setreuid - set real and effective user IDs


     #include <unistd.h>

     setreuid(uid_t ruid, uid_t euid);


     The real and effective user IDs of the current process are set according
     to the arguments. If the real user ID is changed, or the effective user
     ID is changed to a value other than the real user ID, then the saved user
     ID will be set to the effective user ID.

     Unprivileged users may change either user ID to the current value of the
     real, effective, or saved user ID. Only the superuser may make other

     Supplying a value of -1 for either the real or effective user ID forces
     the system to substitute the current ID in place of the -1 parameter.

     The setreuid() function was intended to allow swapping the real and ef-
     fective user IDs in set-user-ID programs to temporarily relinquish the
     set-user-ID value. This purpose is now better served by the use of the
     seteuid() function (see setuid(2)).

     When setting the real and effective user IDs to the same value, the
     setuid() function is preferred.


     Upon successful completion, a value of 0 is returned. Otherwise, a value
     of -1 is returned and errno is set to indicate the error.


     [EPERM]       The current process is not the superuser and a change other
                   than changing the effective user ID to the real user ID was


     getuid(2), seteuid(2), setresuid(2), setuid(2)


     The setreuid() function conforms to the IEEE Std 1003.1-2001 ("POSIX.1")
     and X/Open Portability Guide Issue 4, Version 3 ("XPG4.3"). specifica-

     Note, however, that prior to IEEE Std 1003.1-2001 ("POSIX.1"), the
     setreuid() function was not a part of the IEEE Std 1003.1 ("POSIX.1")
     specification. As a result, it may not be implemented on all systems.


     The setreuid() function call appeared in 4.2BSD. A semantically different
     version appeared in 4.4BSD. The current version, with the original seman-
     tics restored, appeared in OpenBSD 3.3.


     The setreuid() function predates POSIX saved user IDs. This implementa-
     tion changes the saved user ID to the new value of the effective user ID
     if the real user ID is changed. Other implementations may behave dif-

MirBSD #10-current             January 29, 2003                              1

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