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I'm new to docker and I'm having problem creating a symbolic link with the following RUN command:

FROM php:7.3-apache

RUN ["/bin/bash", "-c", "ln -s /app/frontend/web/* /var/www/html"] && \
    ln -s /app/backend/web /var/www/html/admin

Here is the output when doing "ls -la /var/www/html" inside the container:

'*' -> '/app/frontend/web/*'
admin -> /app/backend/web

I'm expecting the following output:

css -> /app/frontend/web/css
index.php -> /app/frontend/web/index.php
admin -> /app/backend/web

I'm getting the correct output when creating the symlink directly in the container but for some reason the wildcard (*) does not work when building the image.

If I'm replacing the wildcard by a specific file, the symlink is creating correctly at build time. This is working but I'd like to avoid listing every files from the folder:

FROM php:7.3-apache

RUN ["/bin/bash", "-c", "ln -s /app/frontend/web/index.php /var/www/html"]

Anyone have a clue on how to do that, I've been searching for a while now and tried different syntax of that RUN command with no success.

EDIT: The symbolic link to my backend works as expected. I also should have noted that I'm using docker-compose and a volume containing my webapp is mounted to the /app folder.

Thanks

aleccentric
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1 Answers1

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When * does not match any files, it is passed as is to your command:

$ ls -l
total 0
-rw-r--r-- 1 leodag leodag 0 jun 17 03:29 a
-rw-r--r-- 1 leodag leodag 0 jun 17 03:29 b
-rw-r--r-- 1 leodag leodag 0 jun 17 03:29 c

$ ls d*
ls: cannot access 'd*': No such file or directory

So your problem is that there is nothing inside /app/frontend/web/, since you still haven't copied the files - you're trying to run it right after the FROM. First you need to copy in your files, so that the glob matches your files. Or else the glob expressions are passed literally to ln, creating a file called *, pointing to a non-existant * file.

FROM php:7.3-apache

COPY myfrontend/ /app/frontend/

RUN ["/bin/bash", "-c", "ln -s /app/frontend/web/* /var/www/html"]
Leonardo Dagnino
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  • I think you are right on. I tried creating a symlink to an empty folder in the container and it does the exact same behavior. I forgot to mention that I have a docker-compose that mounts volume to /app folder, so it should not be empty. Looks like the volume is not mounted yet when trying to create the symbolic link. What is weird is that I have another RUN command right after that one that creates another symlink to my backend (I've shorten my dockerfile for simplicity) and it's working perfectly. This pointed me to the wildcard. I'll edit my initial post to add that info. – aleccentric Jun 17 '20 at 12:10
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    The volume mount happens when you run the container, the Dockerfile is parsed to create the image. During image creation, volume mounts to your defined sources will not exist inside the temporary containers. – BMitch Jun 17 '20 at 12:33
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    Volumes are not mounted at build time - they are exclusively available during runtime. Your build process may not depend on things that will change without Docker noticing things are not up to date, like volumes. Creating symbolic links to files that do not exist works, as long as the filename and paths don't have globs that require expansion by bash. – Leonardo Dagnino Jun 17 '20 at 14:19
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    You could either have your app in the same folder as your Dockerfile, so you can use COPY to put it inside the container, or create each link individually. – Leonardo Dagnino Jun 17 '20 at 14:22
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    Thanks! That makes sense. I've been confused by the fact the symlink for the backend worked. – aleccentric Jun 18 '20 at 11:18