[Bug 1691901] [base-files/zesty] verification still needed

Fri Sep 29 19:29:09 UTC 2017

The fix for this bug has been awaiting testing feedback in the -proposed
repository for zesty for more than 90 days.  Please test this fix and
update the bug appropriately with the results.  In the event that the
fix for this bug is still not verified 15 days from now, the package
will be removed from the -proposed repository.

** Tags added: removal-candidate

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https://bugs.launchpad.net/bugs/1691901

Title:
  [SRU] 50-motd-news costs 5 seconds every login on firewalled systems

Status in base-files package in Ubuntu:
  Fix Released
Status in base-files source package in Zesty:
  Fix Committed
Status in base-files source package in Artful:
  Fix Released

Bug description:
  I noticed quite a long time to login to some of my systems via ssh (or scp).
  Investigating lead me to find out that the '50-motd-news' file
  (/etc/update-motd.d/50-motd-news) was the primary cost.

  In line 108 [1] it does something like:
   curl --connect-timeout "5" --max-time "5" -A "..." -o - https://motd.ubuntu.com

  The systems I'm seeing this on are in a lab and do not have access to https://motd.ubuntu.com.
  The way the lab is configured, they just end up timing out.  So every scp or ssh connection
  or other path to trigger update-motd will cost 5 seconds.

  ======= SRU =======

  [ IMPACT ]

  This bug affects Ubuntu 17.04 systems which cannot reach the internet
  (more specifically, https://motd.ubuntu.com).  There is a bug in the
  implementation of /etc/update-motd.d/50-news whereby the failure of
  the curl fetch of the motd news causes a 5-second delay.  This should
  not be the case.  By design, the motd is fetched in the background, by
  a systemd timer, and refreshed every ~12 hours, also in the
  background.  On login, the script should just cat the cache file.  If
  the cache file isn't found, then it will try to fetch a new motd.  In
  the firewalled system case, the background fetch failed, AND didn't
  create an empty file.  The fix as attached simply ensures that an
  empty file is created if the curl fetch fails.  This eliminates the
  login delay and solves the bug.  Every 12 hours, the curl will be
  retried, quietly in the background, so if the curl failure happened
  for temporary reasons, it'll recover, gracefully, eventually.

  [ TEST CASE ]

  You can either test this on a firewalled system.  Or, if you can hack
  an entry in your local /etc/hosts for motd.ubuntu.com for an invalid
  IP address.  Without the fix, you'll experience a 5 second delay on
  login.  With the fix, you'll login immediately.

  Failure case:

  $ lxc launch ubuntu:17.04 LP1691901
  $ lxc exec LP1691901 bash
  # ssh-import-id kirkland
  # echo 192.168.0.0 motd.ubuntu.com >> /etc/hosts
  # rm -f /var/cache/motd-news
  # exit
  $ time ssh root@$(lxc list | grep LP1691901 | awk '{print $6}') true
  real    0m5.333s
  user    0m0.016s
  sys     0m0.000s

  Apply the fix.

  $ time ssh root@$(lxc list | grep LP1691901 | awk '{print $6}') true
  real    0m0.316s
  user    0m0.008s
  sys     0m0.008s

  [ REGRESSION ]

  This is a simple, safe fix with minimal regression potential:

  diff -Nru base-files-9.6ubuntu13/update-motd.d/50-motd-news base-files-9.6ubuntu13.2/update-motd.d/50-motd-news
  --- base-files-9.6ubuntu13/update-motd.d/50-motd-news   2017-02-15 13:54:04.000000000 -0600
  +++ base-files-9.6ubuntu13.2/update-motd.d/50-motd-news 2017-06-29 10:43:05.000000000 -0500
  @@ -51,9 +51,13 @@
   # If we're not forcing an update, and we have a cached motd-news file,
   # then just print it and exit as quickly as possible, for login performance.
   # Note that systemd should keep this cache file up to date, asynchronously
  -if [ "$FORCED" != "1" ]  && [ -r $CACHE ]; then
  -       echo
  -       safe_print $CACHE
  +if [ "$FORCED" != "1" ]; then
  +       if [ -r $CACHE ]; then
  +               echo
  +               safe_print $CACHE
  +       else
  +               : > $CACHE
  +       fi
          exit 0
   fi

  @@ -111,7 +115,9 @@
                  safe_print "$NEWS"
                  # Try to update the cache
                  safe_print "$NEWS" 2>/dev/null >$CACHE || true
  -       fi
  +       else
  +               : > "$CACHE"
  +       fi
   done
   rm -f "$NEWS" "$NEWS.err"
   exit 0

  --
  [1] https://git.launchpad.net/~usd-import-team/ubuntu/+source/base-files/tree/update-motd.d/50-motd-news?h=applied/ubuntu/zesty#n108

  ProblemType: Bug
  DistroRelease: Ubuntu 17.04
  Package: base-files 9.6ubuntu13
  ProcVersionSignature: User Name 4.10.0-21.23-generic 4.10.11
  Uname: Linux 4.10.0-21-generic x86_64
  ApportVersion: 2.20.4-0ubuntu4
  Architecture: amd64
  Date: Fri May 19 01:11:30 2017
  Ec2AMI: ami-0000004f
  Ec2AMIManifest: FIXME
  Ec2AvailabilityZone: nova
  Ec2InstanceType: m1.small
  Ec2Kernel: unavailable
  Ec2Ramdisk: unavailable
  ProcEnviron:
   TERM=xterm-256color
   PATH=(custom, no user)
   XDG_RUNTIME_DIR=<set>
   LANG=en_US.UTF-8
   SHELL=/bin/bash
  SourcePackage: base-files
  UpgradeStatus: No upgrade log present (probably fresh install)
  mtime.conffile..etc.update-motd.d.50-motd-news: 2017-05-19T01:10:25.572110

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