[Bug 1551351] Re: dhclient does not renew leases

[Stefan Bader]

For more data points on this, someone mentioned today that for him the
leases get renewed (with dhclient started by network-manager).  The
command line is slightly different there:

/sbin/dhclient -d -q -sf <lease-script> -pf <pidfile> -lf <leasefile>
-cf <conffile> <interface>

while on an ifupdown system where I see the stall it is:

/sbin/dhclient -1 -v -pf <pidfile> -lf <ipv4 leasefile> -I -df <ipv6
leasefile> <interface>

though it is the same command line used for ifupdown before. I got another Xenial/ifupdown based VM which was not recently updated (so leases get renewed still). I was able to attach to the daemon with "strace -p <pid> -ff" and could see that the main thread is in "select(7, [5 6], [], NULL, {276, 557923}". But there is other activity as well from time to time.
On the broken system the dhclient main thread is in "futex(0x7fb54906b0a4, FUTEX_WAIT_PRIVATE, 5, NULL" and there is no other activity. As a result the lease gets dropped which I can see on the server side as that is configured to do DNS updates when DHCP leases become active or inactive.

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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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