Exec Console: No bash in some containers

[snoozer]

Hi,

I have tried to use Portainer to access the CLI of the Mosquitto Container without success. I have left the defaults /bin/bash and root. This flickered a black background very quick and brought me beck to where I started. Since I did not see any error message I tried the CLI approach on the host system.

docker exec -it mosquitto /bin/bash

This gave me the following error:
OCI runtime exec failed: exec failed: container_linux.go:370: starting container process caused: exec: "/bin/bash": stat /bin/bash: no such file or directory: unknown

Using /bin/sh instead of /bin/bash then worked, is that intended not to have a bash in the container or is that an oversight ? Is there a way that I can add the bash ?

I have noticed the same issue in the Adminer container as well.

Kind Regards
Jan P.

[Paraphraser]

I agree that it can be annoying. You can add Portainer-CE to your list; neither bash nor sh.

However, whether an image pulled down from Dockerhub has a shell program (or, indeed, any other program) installed inside the image is not something that IOTstack controls. Decisions about what is, or isn't, inside a container are made by whoever builds the image. We IOTstack users just run the image.

If you think a good case can be made for any container that doesn't have a shell program to have that added to its DockerHub image, you need to raise that with whoever maintains the DockerHub image.

I hope that makes sense.

[Paraphraser]

I've realised that I didn't actually answer this part of your question:

Is there a way that I can add the bash

The answer is "yes".

1. Create a Dockerfile. These two lines:

   FROM eclipse-mosquitto
   RUN apk update && apk upgrade && apk add --no-cache bash
   

   need to be in a file at this path:

   ~/IOTstack/services/mosquitto/Dockerfile
   

   You'll notice bash on the end of RUN command. That's adding bash to Mosquitto.

2. If Mosquitto is running, take it down:

   $ cd ~/IOTstack
   $ docker-compose stop mosquitto
   $ docker-compose rm -f mosquitto
   

   That's the equivalent of docker-compose down but it only applies to Mosquitto.

3. Edit docker-compose.yml. At the moment, the first part of the mosquitto chunk looks like this:

     mosquitto:
       container_name: mosquitto
       image: eclipse-mosquitto
       restart: unless-stopped
   

   Make it look like this:

     mosquitto:
       container_name: mosquitto
       build: ./services/mosquitto/.
   #   image: eclipse-mosquitto
       restart: unless-stopped
   

4. Bring up mosquitto with the --build flag:

   $ cd ~/IOTstack
   $ docker-compose up -d --build mosquitto
   

   You'll see a bunch of guff and, towards the end, a mention of installing bash.

5. Test the result:

   $ docker exec -it mosquitto bash
   bash-5.0$ exit
   $
   

   Mosquitto now has bash!

6. Understand what is going on:

   $ docker images | grep -e "REPOSITORY" -e "mosquitto"
   REPOSITORY               TAG         IMAGE ID       CREATED          SIZE
   iotstack_mosquitto       latest      44bcffe814bc   2 minutes ago    11.3MB
   eclipse-mosquitto        latest      c83ed7264442   6 weeks ago      8.08MB
   

   The "iotstack_mosquitto" line is the "local image". It is what has just been built. It only exists on your RPi. It is this image that becomes the running container. The local image has bash and so does the running container.

   The "eclipse-mosquitto" line is the "base image" from DockerHub. That image used to become the running container but it's still needed because the changes we've just made are applied on top.

7. Understand the maintenance problem.

   For most containers you can get updates from DockerHub just by doing this:

   $ cd ~/IOTstack
   $ docker-compose pull
   $ docker-compose up -d
   $ docker system prune
   

   The pull will check for any updates and download any later images, then the up re-creates any containers where the images have been updated. The prune cleans up the mess left behind by any old images.

   Those commands won't work for containers that are built with a local Dockerfile. Node-Red is another example of this problem. If you know that Mosquitto has been updated on DockerHub (and the only way I know of is to go to DockerHub and check), then you need to force it like this:

   $ cd ~/IOTstack
   $ docker-compose build --no-cache --pull mosquitto
   $ docker-compose up -d mosquitto
   $ docker system prune
   

   The "build" with those arguments forces the base image to be re-downloaded from DockerHub, whether it has changed or not. If the base image has actually changed then that, in turn, forces the Dockerfile run and you get a new local image.

Thus, the price you pay for customising an image is not getting automatic updates from Dockerhub.

The question for you is, "is it worth all this just to get bash inside Mosquitto?"

Please don't hear any negative overtones in that question because this is the kind of thing I do on my own IOTstack. I focus on customising Node-Red but that's because:

• it is already built from a Dockerfile so it adds no additional maintenance overheads to use it as the basis of my own customisations; and
• Node-Red is in the middle of everything I do so, if a flow doesn't work, my first question is "what can the container see?". Answering those questions needs add-ons like the mosquitto clients, tcpdump, DNS tools, and so on.

I work from the command line (I don't see the point of Portainer) so I heavily customise the command-line environment with shell scripts and a scheme of aliases. If I want to get into the Node-Red or Mosquitto shells, it's:

$ NODERED_SHELL
$ MOSQUITTO_SHELL

The fact that the first invokes bash while the second invokes sh is kinda unimportant. But I would take this Dockerfile approach if I really needed bash inside Mosquitto.

None of this is to suggest that my way is the "right way" or anything like that. It works for me and it might work for you too.

Hope this helps.

---

If you follow along and then decide you want to undo the changes:

1. Take Mosquitto down.

2. Edit docker-compose.yml to undo the edits.

3. You can leave the Dockerfile where it is or remove it - your choice.

4. Bring Mosquitto up. That will go back to the base image.

5. Run the commands:

   $ docker rmi iotstack_mosquitto
   $ docker system prune
   

You should then be back to where you were.

[Paraphraser]

I'd call this a misunderstanding (not every container has a shell, not every shell is bash). Stale.