From: Joel VanderWerf <vjoel@...>
Date: 2005-07-21T08:15:48+09:00
Subject: Re: Changing Process#uid while staying with $SAFE=0

benny wrote:
> Dear List,
> 
> a have written a daemon that should finally run as a different user than
> root. However I need to initially start as root to get DRb running and want
> to switch the uid of the process after that.
> 
> When I change the uid $SAFE is set to 1. But I need $SAFE to be 0.
> 
> Any idea that I might do? (Running FreeBSD btw.)

Have another thread with $SAFE=0 that exists just to call Process.uid= .
($SAFE is a per-thread variable.) Set this thread up before changing to
$SAFE=1, like this:

# cat safe.rb
Thread.abort_on_exception = true

uid_thread = Thread.new do
  # still $SAFE==0
  sleep # wait for wakeup
  puts "in uid_thread: $SAFE = #{$SAFE}"
  Process.uid=1000
end

$SAFE = 1
puts "in main thread: $SAFE = #{$SAFE}"

uid_thread.wakeup
uid_thread.join

puts "uid = #{Process.uid}"

# ruby safe.rb
in main thread: $SAFE = 1
in uid_thread: $SAFE = 0
uid = 1000