enabling auto completion for apt-get install in docker (ubuntu 14.04)

Question

I am running an ubuntu container in docker. I tried everything I found online, including:

auto-completion does not work for "sudo apt-get install"

but pressing "tab" still has no effect

Solution

I know this is old, but I ran into it too. It's clear what is failing with the help of debug mode in bash: set -x.

Once you get your into your docker container and apt install bash-completion, and edit your users .bashrc to source the right directory, and logout/login (basically follow the steps in the q/a you referenced.

The command that is failing is:

# apt-cache --no-generate pkgnames firefox
E: Could not open file  - open (2: No such file or directory)

The '--no-generate' in there should give you a clue what is going on (something, something, cache is missing). If you run without it, you get back a list of packages.

This led me to search in some of my reference links with how this system is supposed to work, and eventually inspect the apt configuration:

root@edb76551d1dd:/var/cache/apt# apt-config dump |grep Dir::C
Dir::Cache "var/cache/apt/";
Dir::Cache::archives "archives/";
Dir::Cache::srcpkgcache "";
Dir::Cache::pkgcache "";

Notice that 'pkgcache' is empty. Try that on a normal install (like a lxd container), and you will notice it is set. This led me to the place that configuration information is stored, /etc/apt/apt.conf.d/. On the docker container:

# grep cache *
[...]
docker-clean:Dir::Cache::pkgcache ""; Dir::Cache::srcpkgcache "";

You'll notice above that docker images are actively unsetting this value, to keep apt from storing the cache file locally (to reduce image size). I commented out everything in that file, so the file now looks like:

# file: /etc/apt/apt.conf.d/docker-clean 
#DPkg::Post-Invoke { "rm -f /var/cache/apt/archives/*.deb /var/cache/apt/archives/partial/*.deb /var/cache/apt/*.bin || true"; };
#APT::Update::Post-Invoke { "rm -f /var/cache/apt/archives/*.deb /var/cache/apt/archives/partial/*.deb /var/cache/apt/*.bin || true"; };
#Dir::Cache::pkgcache ""; Dir::Cache::srcpkgcache "";

And now, things work (after running apt update once:

# apt update
[...]        
# apt install firefox-d<tab>   
firefox-dbg  firefox-dev

References

These helped me figure out how this system worked...

• auto-completion does not work for "sudo apt-get install"
• https://wiki.ubuntu.com/ReducingDiskFootprint
• https://github.com/debops/ansible-php/issues/22