I believe that changing the uid of a different process can only happen with some deep kernel voodooo. The way it is typically done (via su / sudo) is such:

  1. root process forks
  2. root process drops privileges
  3. now non-root process fork/execs to the new process

If the process is trusted, it may only do steps 1 and 2, and possibly retake privileges later.

See the $<, $>, $(, and $) variables in perlvar.

Update: added links

Update 2: This is not an endeavor to be take lightly. Test for success on everything involving dropping your privileges. Understand the implications of what you are attempting to do. Root escalations have occurred because assumptions made by an application were violated.

--MidLifeXis

In reply to Re: How to change the userid of a running external process by MidLifeXis
in thread How to change the userid of a running external process by macron0

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