Question / Bug - Fresh Ubuntu 26.04 with Repository from Docker (Problems with Volumes in Docker-Compose.Yaml File)

[Unknown-Players]

Hi everyone,

Maybe someone can help me.

I have an Ubuntu Server 26.04 LTS that I just installed yesterday, and I'm experiencing some strange behavior.

I installed Mailu, and that's fine so far.

Now, I read on Mailu's GitHub page that you can use the plugins you want with Roundcube if you do the following: Mailu/Mailu#545

Specifically, you're supposed to write a plugin directory and the config.inc.php file.

I know that this is exactly how it used to work.

volumes:

• "/opt/appdata/mailu/webmail:/data"

• "/opt/appdata/mailu/overrides/roundcube:/overrides:ro"

• "./webmail/config.inc.php:/var/www/roundcube/config/config.inc.php"

Whether I specify the path like this or an absolute path makes absolutely no difference; it writes what would normally be a file as a directory. Regarding the plugin directory, it's created correctly, but then the content is empty. Normally, there are 30 or 40 subdirectories containing the plugins.

I checked to make sure the files were in the correct locations.

My question is whether this is a current bug because the entire server was reinstalled yesterday, so I'm ruling that out as the cause. I used the appropriate Docker repository for Ubuntu, (https://docs.docker.com/engine/install/ubuntu/) as recommended on the official website, and installed it exactly as instructed. Therefore, my question is: what's the problem, or how can I fix it? It seems to be a general mounting issue.

Thank you for your help.

[glours]

Hello @Unknown-Players

This looks like expected bind-mount behavior, not necessarily a Compose bug.

With the short volume syntax:

• ./webmail/config.inc.php:/var/www/roundcube/config/config.inc.php

Docker Compose can create the missing source path on the host as a directory. So if ./webmail/config.inc.php does not already exist as a file before running docker compose up, it may be created as a directory and then mounted over the file path in the container.

Relevant docs:

• Docker bind mounts: https://docs.docker.com/engine/storage/bind-mounts/
• Compose file reference, volumes: https://docs.docker.com/reference/compose-file/services/#volumes
• Compose specification, create_host_path: https://github.com/compose-spec/compose-spec/blob/main/spec.md#long-syntax-5

To avoid this, make sure the file exists first:

mkdir -p ./webmail
touch ./webmail/config.inc.php

Then use the long syntax with create_host_path: false:

services:
  your-service:
    volumes:
      - type: bind
        source: ./webmail/config.inc.php
        target: /var/www/roundcube/config/config.inc.php
        read_only: true
        bind:
          create_host_path: false

You can also verify the resolved path with:

  docker compose config
  ls -la ./webmail/config.inc.php
  file ./webmail/config.inc.php

For the plugin directory: if you bind-mount an empty host directory over a directory inside the container, the container’s existing files in that path are hidden by the mount. So make sure the host directory contains the expected plugin files before mounting it.

[Unknown-Players]

Hi, thanks for the reply.

Okay, the thing with the Config.inc.php worked.

I'm not sure what to do about the empty directory.

Because I looked directly at the container before, and it was full of subdirectories, which in turn contained files.

But when I mount /srv/mount:/local/mount/directory, the /srv/mount directory is simply empty, regardless of whether I use the shortened or long version. The strange thing is that the directory on the container is also empty. Something's not right. Shouldn't it be that when I mount a directory from the container, it displays the contents or copies them there?

for Example this is my Line for Plugins:

• "/opt/appdata/mailu/webmail/plugins:/var/www/roundcube/plugins"

but not work create only a empty directory

have i now understand correctly i must first all file from container to local right (copy job) then i can mount this one right?
But I'm sure that in the past, you could specify it, and files were written out during creation. Was that a bug or not intended?