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I run a centos 8 distro on docker and I would like to have bash TAB completion with dnf package manager. According to other posts, I did the following once my docker container is started:

dnf clean all && rm -r /var/cache/dnf && dnf upgrade -y && dnf update -y

and then

dnf install bash-completion sqlite -y

After doing that I restart the container but there is still no bash completion. I also tried to source directly the bash completion file by doing:

source /etc/profile.d/bash_completion.sh

but without any better effect.

Would you know what I am doing wrong ?

Eurydice
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1 Answers1

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You shouldn't need BASH Completion in a Docker container. The only time you should be manually connecting to a shell inside a Linux container is to troubleshoot why the process running in the container is behaving abnormally. In fact, some container design advice might even go as far as suggesting you not include a shell inside your base OS at all!

The reason this isn't working for you is due to the way in which Linux containers operate. A Container is simply a namespaced process that is managed by the kernel installed on the Host OS. This process cannot be modified or interrupted or the container will be destroyed since the process will be sent a SIGTERM. When you attempt to source the bash_completion.sh script, you are attempting to pass new configuration arguments to your existing namespaced process managed by Docker.

If you really wanted to do this the best way to do it would be to create a new Docker Container Image based on the original CentOS 8 Base Image. And then from there install the bash completion package and add an echo command to add the source line to your user's .bashrc file.

EDIT:

With regards to the additional question asked OP in the comments of this answer I have added additional information below.

Why should not I need bash completion in a container

The reason you do not need bash completion in a container is because containers are not meant to be attached to with a shell. A is simply supposed to be a single instance of a process running under specific configured criteria. Containers aren't meant to be used to create dev environments for you to connect to, they're meant to run processes and applications in software infrastructure.

Manually updating & installing packages

You mention that one of the first things you do when you spin up a container is install packages. This is also alarming to me because you are not supposed to be manually interacting with a container at all. This includes package installation. Instead, you should generate a new Container Image from the older Base Image and add additional RUN statements to the Dockerfile to update the system and install these desired packages.

Cannot believe it is not possible

It is possible if you create a new Dockerfile that purposely installs it on a new layer of the base image and produces a new container image for you to use. BUT the point is that you shouldn't be connecting to Docker containers in the first place to even get to a point where you could need something like bash completion!

Here is a great summary on the difference between a container and a virtual machine that might help clarify some of this for you. In a nutshell, containers are supposed to run, and only run, processes.

TJ Zimmerman
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    I feel sorry but I do not see your point. Maybe I misunderstood. Why should not I need bash completion in a container ? One of the first thing we usually do when starting a container is 1) update of the packages 2) installing some packages. So for point 2) having tab completion is highly needed. For that very reason, I can not believe that it is not possible. – Eurydice Mar 28 '20 at 10:27
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    I added additional information to my answer in the section at the bottom titled EDIT. The fundamental misunderstanding you are having is how Docker containers are meant to be used. Once a container spec has been defined and the container has been created you should never be connecting to it unless you need to troubleshoot something with the application running inside it. Gaining shell access into a container is rare. So fare that it is strange to want to install bash completion inside it. I work professionally with this stuff and might exec into a container once every two weeks at most. – TJ Zimmerman Mar 28 '20 at 16:54
  • ok. I see your point and I agree in some way. But I sill think bash completion can be useful. I know about using RUN commands. However, say that you use a distro with which you are not comfortable with (centos in my case). Before compiling the set of RUN commands you will include in your Dockerfile, you would be happy to dig for them inside the container directly. For instance a given package does not have the same name under ubuntu or centos (NetCDF library for instance).Anyway, thanks for your help and explanations. – Eurydice Mar 30 '20 at 07:16