The remaining autopkgtests regressions (nplan/amd64 and gvfs/s390x) are
also unrelated to this change.

- nplan/amd64 passed with 3 retests:

Before:

  test_mix_bridge_on_bond (__main__.TestNetworkManager) ... FAIL
  ...
  integration.py       FAIL non-zero exit status 1

After:

  test_mix_bridge_on_bond (__main__.TestNetworkManager) ... ok
  ...
  integration.py       PASS


- gvfs/s390x has a long history of flaky/likely failures on these 2 tests, as 
seen in

  https://autopkgtest.ubuntu.com/packages/gvfs/xenial/s390x

So it is OK to ignore this one, it's not a regression from _this_
change.

Examples:

1.28.2-1ubuntu1~16.04.3         systemd/229-4ubuntu21.23
2019-12-02 13:31:15 UTC         0h 41m 38s      mfo     fail

  trash:// deletion, attributes, restoring for a file in $HOME (API) ... FAIL
  trash:// deletion, attributes, restoring for a file in $HOME (CLI) ... FAIL

1.28.2-1ubuntu1~16.04.3         systemd/229-4ubuntu21.23
2019-11-27 22:19:05 UTC         0h 02m 29s      ddstreet        fail

  trash:// deletion, attributes, restoring for a file in $HOME (API) ... ok
  trash:// deletion, attributes, restoring for a file in $HOME (CLI) ... FAIL

with a previous, anecdotal entry of 6 retests until passing on:

1.28.2-1ubuntu1~16.04.2         apache2/2.4.18-2ubuntu3.9       2018-06-29 
18:31:14 UTC         0h 
02m 47s         ahasenack       pass    

  trash:// deletion, attributes, restoring for a file in $HOME (API) ... ok
  trash:// deletion, attributes, restoring for a file in $HOME (CLI) ... ok

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https://bugs.launchpad.net/bugs/1846787

Title:
  systemd-logind leaves leftover sessions and scope files

Status in dbus package in Ubuntu:
  Fix Released
Status in systemd package in Ubuntu:
  Fix Released
Status in dbus source package in Xenial:
  Fix Committed
Status in systemd source package in Xenial:
  Fix Committed

Bug description:
  [Impact]
  Scope file leakage can cause SSH delays and reduce performance in systemd

  [Description]
  The current systemd-logind version present in Xenial can leave abandoned SSH
  sessions and scope files in cases where the host sees a lot of concurrent SSH
  connections. These leftover sessions can slow down systemd performance
  greatly, and can have an impact on sshd handling a great number of concurrent
  connections.

  To fix this issue, patches are needed in both dbus and systemd. These improve 
the
  performance of the communication between dbus and systemd, so that they can
  handle a better volume of events (e.g. SSH logins). All of those patches are
  already present from Bionic onwards, so we only need those fixes for Xenial.

  == Systemd ==
  Upstream patches:
  - core: use an AF_UNIX/SOCK_DGRAM socket for cgroup agent notification 
(d8fdc62037b5)

  $ git describe --contains d8fdc62037b5
  v230~71^2~2

  $ rmadison systemd
   systemd | 229-4ubuntu4     | xenial          | source, ...
   systemd | 229-4ubuntu21.21 | xenial-security | source, ...
   systemd | 229-4ubuntu21.22 | xenial-updates  | source, ... <--------
   systemd | 237-3ubuntu10    | bionic          | source, ...
   systemd | 237-3ubuntu10.29 | bionic-security | source, ...
   systemd | 237-3ubuntu10.29 | bionic-updates  | source, ...
   systemd | 237-3ubuntu10.31 | bionic-proposed | source, ...

  == DBus ==
  Upstream patches:
  - Only read one message at a time if there are fds pending (892f084eeda0)
  - bus: Fix timeout restarts  (529600397bca)
  - DBusMainLoop: ensure all required timeouts are restarted (446b0d9ac75a)

  $ git describe --contains 892f084eeda0 529600397bca 446b0d9ac75a
  dbus-1.11.10~44
  dbus-1.11.10~45
  dbus-1.11.16~2

  $ rmadison dbus
   dbus | 1.10.6-1ubuntu3    | xenial           | source, ...
   dbus | 1.10.6-1ubuntu3.4  | xenial-security  | source, ...
   dbus | 1.10.6-1ubuntu3.4  | xenial-updates   | source, ... <--------
   dbus | 1.12.2-1ubuntu1    | bionic           | source, ...
   dbus | 1.12.2-1ubuntu1.1  | bionic-security  | source, ...
   dbus | 1.12.2-1ubuntu1.1  | bionic-updates   | source, ...

  [Test Case]
  1) Simulate a lot of concurrent SSH connections with e.g. a for loop:
  multipass@xenial-logind:~$ for i in {1..1000}; do sleep 0.1; ssh localhost 
sleep 1 & done

  2) Check for leaked sessions in /run/systemd/system/:
  multipass@xenial-logind:~$ ls -ld /run/systemd/system/session-*.scope*
  drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-103.scope.d
  drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-104.scope.d
  drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-105.scope.d
  drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-106.scope.d
  drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-110.scope.d
  drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-111.scope.d
  drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-112.scope.d
  drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-113.scope.d
  drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-114.scope.d
  drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-115.scope.d
  drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-116.scope.d
  drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-117.scope.d
  drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-118.scope.d
  drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-119.scope.d
  drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-120.scope.d
  drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-121.scope.d
  drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-122.scope.d
  drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-123.scope.d
  drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-126.scope.d
  drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-131.scope.d
  drwxr-xr-x 2 root root 160 Oct 4 15:34 /run/systemd/system/session-134.scope.d
  ...

  [Regression Potential]
  As the patches change the communication socket between dbus and systemd, 
possible regressions could cause systemd to not be notified of dbus events and 
vice-versa. We could see units not getting started properly, and communication 
between different services break down (e.g. between systemd-logind and other 
processes).

  In this case, the regression potential should be low as these patches
  have seen extensive testing both upstream and in more recent releases
  of Ubuntu. Nonetheless, these new packages will be rigorously tested
  through autopkgtest to avoid any possible Xenial-specific regressions.

To manage notifications about this bug go to:
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