Kernel parameter fs.may_detach_mounts is necessary even if mount flag is set to slave

[jamiejackson]

I just discovered this role today. It covers a lot of bases, but it might be missing one.

I had been having issues on my host (with another Docker role, FWIW) until I added the following:

    - name: 'may_detach_mounts workaround (https://github.com/moby/moby/pull/34886 & https://github.com/moby/moby/issues/34538#issuecomment-331533940)'
      become: yes
      copy:
        content: |
          fs.may_detach_mounts=1
        dest: /etc/sysctl.d/may_detach_mounts.conf
      register: may_detach_mounts_config
    
    - name: activate may_detach_mounts
      command: sysctl -p  /etc/sysctl.d/may_detach_mounts.conf
      become: yes
      when: may_detach_mounts_config.changed

I see this (https://github.com/haxorof/ansible-role-docker-ce/blob/master/tasks/main-Mountflags.yml) but IIRC, I'd encountered an issue even with that set.

Thoughts?

References:

• Cannot delete dead containers with overlay2 on RHEL 7.4 moby/moby#34538 (comment)
• Automatically set may_detach_mounts=1 on startup moby/moby#34886

[haxorof]

Thanks @jamiejackson for letting me know about this. I will have a look at it and read the links you provided.