[Bug 1551351] Re: dhclient does not renew leases

[Stefan Bader]

I believe I got a vague feeling about what is going wrong. So the isc
library which now is shared for bind9 and dhcp is compiled (because
bind9 is rather wanted that way) with threads enabled. Before that the
export version of the library was not. So an isc_app which dhclient
creates and runs was more or less a loop handling events. Now this
creates a series of threads.

The problem looks to be that dhclient (and probably dhcpd, too) set up
the isc_app context and then do a fork() (in daemon mode). The man page
of fork() clearly states that the child will be single threaded. So when
dhclient calls dispatch() to run the isc_app this probably only runs a
single control loop more or less waiting for the threads (which do not
run, maybe not even exist anymore) to do the work.

The signal handling might be related to that as well. With threads only
one of them should handle signals and somehow synchronize with the rest.
Maybe the new library is not handling that correctly. Since this does
not work regardless of running as daemon or not. But I have not
understood all the details there.

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https://bugs.launchpad.net/bugs/1551351

Title:
  dhclient does not renew leases

Status in bind9 package in Ubuntu:
  Confirmed
Status in isc-dhcp package in Ubuntu:
  Confirmed
Status in bind9 source package in Xenial:
  Confirmed
Status in isc-dhcp source package in Xenial:
  Confirmed

Bug description:
  Release: Xenial

  I think this only recently started after some bind9 updates triggered a rebuild. When booting dhclient gets started and acquires an IP address, but it does seem to lock up somewhere as it does not renew the lease.
  In my environment I set the lease time to 5 minutes, so I notice such things rather soon. I looked on the dhcp server side but saw any further dhcp messages come in from the client side.

  Related bugs:
   * bug 1551415:  systemctl stop networking hang / timeout 

  ProblemType: Bug
  DistroRelease: Ubuntu 16.04
  Package: isc-dhcp-client 4.3.3-5ubuntu8
  ProcVersionSignature: Ubuntu 4.4.0-9.24-generic 4.4.3
  Uname: Linux 4.4.0-9-generic x86_64
  ApportVersion: 2.20-0ubuntu3
  Architecture: amd64
  Date: Mon Feb 29 12:32:52 2016
  DhclientLeases:

  SourcePackage: isc-dhcp
  UpgradeStatus: No upgrade log present (probably fresh install)

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