[Bug 1578663] Update Released

[Martin Pitt]

The verification of the Stable Release Update for systemd has completed
successfully and the package has now been released to -updates.
Subsequently, the Ubuntu Stable Release Updates Team is being
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the event that you encounter a regression using the package from
-updates please report a new bug using ubuntu-bug and tag the bug report
regression-update so we can easily find any regressions.

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https://bugs.launchpad.net/bugs/1578663

Title:
  create DHCP exit hook for setting NTP servers through dhclient

Status in systemd package in Ubuntu:
  Fix Released
Status in systemd source package in Xenial:
  Fix Released
Status in systemd source package in Yakkety:
  Fix Released

Bug description:
  Similar to /etc/dhcp/dhclient-exit-hooks.d/ntpdate, we should ship a
  DHCP exit hook for timesyncd to update the timesyncd configuration in
  /run/systemd/timesyncd.conf.d/01-dhclient.conf to set the picked up
  NTP servers, and restart timesyncd.

  SRU INFORMATION
  ===============
  Rationale: This is a regression compared to trusty where we used ntpdate; /etc/dhcp/dhclient-exit-hooks.d/ntpdate ran ntpdate on the new NTP servers. This causes timesyncd to always try and talk to the disto configured server (ntp.ubuntu.com) which might be disallowed by firewall rules or other networking policy. Thus machines in such an environment never get a correct time sync even when they get a local NTP server advertised over DHCP (unless they use systemd-networkd, which is not done by default in Xenial).

  Test case:
  - Set up a DHCP server that includes NTP information. For example, you can set LXC_DHCP_CONFILE=/etc/lxc/dnsmasq.conf in /etc/default/lxc-net, and create /etc/lxc/dnsmasq.conf with "dhcp-option=option:ntp-server,4.3.2.1", restart lxc-net, and then run QEMU on lxcbr0 instead of the builtin network.
  - In the client machine, disconnect and reconnect the network (e. g. "sudo ifdown ens3; sudo ifup ens3").
  - Check in "systemctl status systemd-timesyncd" that timesyncd tries to sync with the given NTP server (for the bogus 4.3.2.1 it will fail, but the point is that it did try).

  Regression potential: A broken dhclient-exit-hooks.d has the potential
  to break subsequent hooks. dhclient-scripts runs the hooks without
  "set -e", but syntax errors can still cause damage. Thus it should be
  verified that later hooks (e. g. /etc/dhcp/dhclient-exit-hooks.d
  /zzz_avahi-autoipd) still run. Beyond that there is little potential
  for regression as

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