[Bug 1551351] Re: dhclient does not renew leases

[Stefan Bader]

Hm, of course, if one starts dhclient in debug mode (foreground) by adding a "-d", everything does work. :/ Interestingly when I attach to it with strace, I see "strace: Process <pid> attached with 4 threads". The foreground process does not act on ctrl-c which at least is consistent with the broken behaviour.
When not working (in the background) strace will not find/report any threads running. The other thing to note (it was mentioned before) is that looking at /proc/<pid>/fd the process has a file handle for the lease file, but looking at the time stamps it does not get updated. Likely because that is something that one of the threads would do.
This also explains why dhclient under network-manager control works. Network-manager starts it in foreground/debug mode (with -d).

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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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