[Bug 1546214] Re: Docker containers lose their cgroup after systemd reload

[Martin Pitt]

I was about to point out the Delegate= option if docker.service wants to
maintain its sub-cgroups by itself -- but it seems that already landed
upstream two days ago: https://github.com/jheiss/docker/commit/64b87f0

There have been plenty of discussions about that "who owns the cgroup
hiearchy"/"single writer" topic, and I don't think this will change
anytime soon (nor will we change the behaviour downstream), so I'll
close the systemd task.

I'll see to pulling this patch into Xenial's docker.

** Changed in: docker.io (Ubuntu)
       Status: Confirmed => In Progress

** Changed in: systemd (Ubuntu)
       Status: Confirmed => Won't Fix

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https://bugs.launchpad.net/bugs/1546214

Title:
  Docker containers lose their cgroup after systemd reload

Status in docker.io package in Ubuntu:
  In Progress
Status in systemd package in Ubuntu:
  Won't Fix

Bug description:
  
  After a Systemd reload & any service restart, docker top no longer show process of containers:

  To reproduce this issue, do the following step:

  # docker run -d --name test busybox sleep 1d
  # docker top test
  UID                 PID                 PPID                C                   STIME               TTY                 TIME                CMD
  root                26416               1072                1                   18:05               ?                   00:00:00            sleep 1d
  # systemctl --system daemon-reload && systemctl restart atd.service
  # docker top test
  UID                 PID                 PPID                C                   STIME               TTY                 TIME                CMD
  [  no process listed... but sleep is still running]

  Note: this idea of restarting any service restart come from patch
  https://lists.freedesktop.org/archives/systemd-
  devel/2014-September/023276.html (which is applied to Systemd package
  in Ubuntu)

  
  After few searching, this seems to be due to process from the container being moved in other cgroup by Systemd. More details on https://github.com/docker/docker/issues/20152

  Depending on version of Systemd (Wily or Xenial), this issue:

  * Wily: Happend with Docker 1.10 (with default option)
  * Wily: Does NOT happend with Docker 1.10 and --exec-opt native.cgroupdriver=systemd
  * Wily: Does NOT happend with Docker 1.9
  * Xenial: Does always happend (Docker 1.9, 1.10 with or without native.cgroupdriver=systemd)

  
  I don't know if this issue is a Systemd issue, a Docker issue... or in middle.

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