NAME
    Unix::SavedIDs - interface to unix saved id commands: getresuid(),
    getresgid(), setresuid() and setresgid()

SYNOPSIS
        use Unix::SavedIDs;

            my($ruid,$euid,$suid) = getresuid();
            setresuid(10,10,10);

STATUS
    This is alpha code. I'm going to be using it a lot in production and
    once I'm comfortable that it's working well I'll up the version number
    to 1.0 and call it a production release.

DESCRIPTION
    This module is a simple interface to the c routines with the same names.

    If you want to drop root privileges, see Unix::SetUser. This provides a
    simple interface, uses Unix::SavedIDs to handle saved ids, handles
    supplemental groups and generally makes dropping root privileges easy
    and secure.

    If you want to drop root privileges, use Unix::SetUser or this module,
    Unix::SavedIDs. Seriously.

    $<, $>, $(, $) and the POSIX setuid(),seteuid etc... functions give you
    access to the real uid/gid (ruid/rgid) and effective uid/gid
    (*euid*/*egid*), but there was no way to get or set the saved uid/gid
    (*suid*/*sgid*).

WHY THIS MATTERS
            # start as root
            die if $> != 0;
            # I think this should drop root 
            $( = 50;
            $) = "50 50";
            $> = 50;
            $< = 50;
            # Make sure I dropped root
            print "\$< = $<\n";
            print "\$> = $>\n";
            # I really dropped root, right?  
            # So, I can't possibly switch back.
            $< = 0;
            $> = 0;
            print "\$< = $<\n";
            print "\$> = $>\n";
            # oh crap....

    The effective user id changed back to root. If someone cracks your
    script, they can get root.

FUNCTIONS
  getresuid()

    returns a list of 3 elements, the current *ruid*, *euid* and *suid* or
    croaks on failure.

  getresgid()

    returns a list of 3 elements, the current *rgid*, *egid* and *sgid* or
    croaks on failure.

  setresuid(*ruid*,*euid*,*suid*)

    Sets the current *ruid*, *euid* and *suid* or croaks on failure.

    Any arguments which are unset,undef or -1 tells setresuid to leave that
    value unchanged. E.G.

      setresuid(500);
      setresuid(500,undef,undef);
      setresuid(500,-1,-1);

    ... all will set the *ruid* to 500 and leave the *euid* and *suid* alone
    and:

      setresuid(undef,undef,500)

    ... will set your *suid* to 500 and leave your *ruid* and *euid*
    unchanged.

    setresgid behaves in the same way.

  setresgid(*rgid*,*egid*,*sgid*)

    Sets the current *rgid*, *egid* and *sgid* or croaks on failure.

    Please see setresuid() above to see how to leave an id unchanged.

ACKNOWLEDGMENTS
    I recently discovered Proc::UID by Paul Fenwick. It does everything that
    this module does plus more. Sadly, its unmaintained since 2004 and the
    author specifically states that it is not for production code.

BUGS AND LIMITATIONS
    Installer doesn't check directly for saved ids. Instead it assumes
    anything non posix won't do saved ids. That isn't necessarily true.

    I only have Linux and OpenBSD systems to test on, so I have no idea how
    it might work on other operating systems. If you run a different OS,
    please let me know how this module works in your environment.

    Please report any bugs or feature requests to
    `bug-unix-savedids@rt.cpan.org', or through the web interface at
    http://rt.cpan.org.

AUTHOR
    Dylan Martin `<dmartin@cpan.org>'

LICENSE AND COPYRIGHT
    Copyright (c) 2008, Dylan Martin & Seattle Central Community College
    `<dmartin@cpan.org>'.

    Permission to use, copy, modify, and distribute this software for any
    purpose with or without fee is hereby granted, provided that the above
    copyright notice and this permission notice appear in all copies.

DISCLAIMER
    THE SOFTWARE IS PROVIDED "AS IS" AND THE AUTHOR DISCLAIMS ALL WARRANTIES
    WITH REGARD TO THIS SOFTWARE INCLUDING ALL IMPLIED WARRANTIES OF
    MERCHANTABILITY AND FITNESS. IN NO EVENT SHALL THE AUTHOR BE LIABLE FOR
    ANY SPECIAL, DIRECT, INDIRECT, OR CONSEQUENTIAL DAMAGES OR ANY DAMAGES
    WHATSOEVER RESULTING FROM LOSS OF USE, DATA OR PROFITS, WHETHER IN AN
    ACTION OF CONTRACT, NEGLIGENCE OR OTHER TORTIOUS ACTION, ARISING OUT OF
    OR IN CONNECTION WITH THE USE OR PERFORMANCE OF THIS SOFTWARE.