title: binfmt_misc problems in ubuntu18.04 under docker
body: <p>Trying to get a cross chroot running under ubuntu:18.04 in a docker container.</p>
  
  <p>While trying to install <code>binfmt-support</code> (dependency of <code>qemu-user-static</code>) this happens:</p>
  
  <pre><code>~ docker run -it ubuntu:18.04 /bin/bash
  root@df5a34a47fe2:/# cd
  root@df5a34a47fe2:~# apt-get update
  ...
  root@df5a34a47fe2:~# apt-get install qemu-user-static
  ...
  Setting up qemu-user-static (1:2.11+dfsg-1ubuntu7.9) ...
  mount: /proc/sys/fs/binfmt_misc: permission denied.
  update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
  mount: /proc/sys/fs/binfmt_misc: permission denied.
  update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
  mount: /proc/sys/fs/binfmt_misc: permission denied.
  update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
  mount: /proc/sys/fs/binfmt_misc: permission denied.
  update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
  mount: /proc/sys/fs/binfmt_misc: permission denied.
  update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
  mount: /proc/sys/fs/binfmt_misc: permission denied.
  update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
  mount: /proc/sys/fs/binfmt_misc: permission denied.
  update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
  mount: /proc/sys/fs/binfmt_misc: permission denied.
  update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
  mount: /proc/sys/fs/binfmt_misc: permission denied.
  update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
  mount: /proc/sys/fs/binfmt_misc: permission denied.
  update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
  mount: /proc/sys/fs/binfmt_misc: permission denied.
  update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
  mount: /proc/sys/fs/binfmt_misc: permission denied.
  update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
  mount: /proc/sys/fs/binfmt_misc: permission denied.
  update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
  mount: /proc/sys/fs/binfmt_misc: permission denied.
  update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
  mount: /proc/sys/fs/binfmt_misc: permission denied.
  update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
  mount: /proc/sys/fs/binfmt_misc: permission denied.
  update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
  mount: /proc/sys/fs/binfmt_misc: permission denied.
  update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
  mount: /proc/sys/fs/binfmt_misc: permission denied.
  update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
  mount: /proc/sys/fs/binfmt_misc: permission denied.
  update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
  mount: /proc/sys/fs/binfmt_misc: permission denied.
  update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
  mount: /proc/sys/fs/binfmt_misc: permission denied.
  update-binfmts: warning: Couldn't mount the binfmt_misc filesystem on /proc/sys/fs/binfmt_misc.
  Setting up binfmt-support (2.1.8-2) ...
  invoke-rc.d: could not determine current runlevel
  invoke-rc.d: policy-rc.d denied execution of start.
  root@df5a34a47fe2:~# echo $?
  0
  </code></pre>
  
  <p>Does anybody know what's happening here, if it's relevant and how to fix it?</p>