blog/data/2012-01-03-skolelinux.txt

   1 Title: Fixing an hanging debian installer for Debian Edu
   2 Tags: english, debian edu
   3 Date: 2012-01-03 11:25
   4
   5 <p>During christmas, I have been working getting the next version of
   6 <a href="http://www.skolelinux.org/">Debian Edu / Skolelinux</a> ready
   7 for release.  The initial problem I looked at was particularly
   8 interesting.</p>
   9
  10 <P>The installer would hang at the end when it was doing it
  11 post-installation configuration, and whatevery I did to try to find
  12 the cause and fix it always worked while I tested it, but never when I
  13 integrated it into the installer and ran the installation from
  14 scratch.  I would try to restart processes, close file descriptors,
  15 remove or create files, and the installer would always unblock and
  16 wrap up its tasks.</p>
  17
  18 <p>Eventually the cause was found.  The kernel was simply running out
  19 of entropy, causing the Kerberos setup to hang waiting for more.
  20 Pressing keys was adding entropy to the kernel, and thus all my tries
  21 to fix the problem worked not because what I was typing to fix it, but
  22 because I was typing.</P>
  23
  24 <p>The fix I implemented was to add a background process looking at
  25 the level of entropy in the kernel (by checking
  26 /proc/sys/kernel/random/entropy_avail), and if it was too small, the
  27 installer will flush the kernel file buffers and do 'find /' to
  28 generate some disk IO.  Disk IO generate entropy in the kernel, and is
  29 one of the few things that can be initated from within the system to
  30 generate entropy.</p>
  31
  32 <p>The fix is in
  33 <a href="http://wiki.debian.org/DebianEdu/Documentation/Squeeze/Installation">beta1
  34 of the Debian Edu/Squeeze</a> version, and we
  35 <a href="http://wiki.debian.org/DebianEdu">welcome more testers and
  36 developers</a>.  We plan to release beta2 this weekend.</p>