docker can't be uninstalled if it never worked (Ubuntu)

[dbanck]

Uninstallation will fail because the prerm script cannot stop the docker instance (because none is running):

root@hv ~ # aptitude purge lxc-docker
The following packages will be REMOVED:  
  lxc-docker{p} 
0 packages upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
Need to get 0 B of archives. After unpacking 4,483 kB will be freed.
Do you want to continue? [Y/n/?] 
(Reading database ... 56846 files and directories currently installed.)
Removing lxc-docker ...
stop: Unknown instance: 
dpkg: error processing lxc-docker (--purge):
 subprocess installed pre-removal script returned error exit status 1
docker start/running, process 11949
Errors were encountered while processing:
 lxc-docker
E: Sub-process /usr/bin/dpkg returned an error code (1)
A package failed to install.  Trying to recover:

This script causes the problem /var/lib/dpkg/info/lxc-docker.prerm (docker/packaging/ubuntu/lxc-docker.prerm)

#!/bin/sh

# Stop docker
/sbin/stop docker

The script should only try to stop docker if an instance is running.

[mzdaniel]

Thank you, Daniel!. Good catch. This has been done in the Debian package, I'll correct this.

[terrywang]

I had pretty much the same problem on Ubuntu 12.04.

Error

# apt-get purge lxc-docker 
Reading package lists... Done
Building dependency tree       
Reading state information... Done
The following package was automatically installed and is no longer required:
  bsdtar
Use 'apt-get autoremove' to remove them.
The following packages will be REMOVED:
  lxc-docker*
0 upgraded, 0 newly installed, 1 to remove and 0 not upgraded.
After this operation, 4,753 kB disk space will be freed.
Do you want to continue [Y/n]? y
(Reading database ... 235601 files and directories currently installed.)
Removing lxc-docker ...
stop: Unknown instance: 
dpkg: error processing lxc-docker (--purge):
 subprocess installed pre-removal script returned error exit status 1
docker start/running, process 1841
Errors were encountered while processing:
 lxc-docker
localepurge: Disk space freed in /usr/share/locale: 0 KiB
localepurge: Disk space freed in /usr/share/man: 0 KiB
localepurge: Disk space freed in /usr/share/gnome/help: 0 KiB
localepurge: Disk space freed in /usr/share/omf: 0 KiB

Total disk space freed by localepurge: 0 KiB

E: Sub-process /usr/bin/dpkg returned an error code (1)

To workaround it, I just did a dirty trick, commented out /sbin/stop docker in the pre-removal script /var/lib/dpkg/info/lxc-docker.prerm and it went through.

[mzdaniel]

@dbanck, @terrywang could you verify the following patch works for you?

41cdd9b