Confusing "Permission denied" when data directory doesn't exist

[okurka12]

Scenario

Be me, entirely new to Radicale, setting it up as a docker container. Somehow I mismatch the directory specifications in config and compose. It shows me Permission denied, so I just force root user to resolve it. What could possibly go wrong?

How it happened

So for example in docker-compose I am mounting /var/lib/radicale but I specified /data in the config (don't ask, maybe I copied some config from somewhere, maybe AI hallucinated it, whatever). The logs look like this:

[2026-06-14 01:00:49 +0000] [1] [INFO] Storage location: '/data/collections'
[2026-06-14 01:00:49 +0000] [1] [WARNING] Storage location: '/data/collections' does not exist, creating now
[2026-06-14 01:00:49 +0000] [1] [ERROR] Directory permissions: path='/' owner=root(0) group=root(0) mode=40755 / Effective user: user=radicale(1000) groups=radicale(1000),radicale(1000)
[2026-06-14 01:00:49 +0000] [1] [CRITICAL] An exception occurred during server startup: [Errno 13] Permission denied: '/data'

I look at the last line and see Permission denied. I don't think much about it, I just add user: "0:0" to my compose file, it works, I get on with my life.

What I don't realize is that instead of storing the persisnent data in the mounted directory, it stores them in a dicrectory that it itself created within the container. Then my server restarts a week later during an unattended upgrade and the data is gone? 😅 (Luckily i could just export everything from thunderbird offline cache, but it still gave me a little heart attack)

Conclusion

Maybe this is a skill issue on my side but I think it could be improved how this error is communicated to prevent others from doing what I just did. Perhaps Radicale could be smart and refuse to operate if both the configured directory doesn't exist and it is running in a container.

[pbiering]

@kalsi-avneet - can you please check?

[kalsi-avneet]

@okurka12 ,

Then my server restarts a week later during an unattended upgrade and the data is gone?

I do not know the complete details of your setup, but I believe that unless the container was started with --rm, or explicitly set to be deleted via some automatic script, the data inside the container can be recovered. If you could share some more details, I will be glad to help you with that.

Perhaps Radicale could be smart and refuse to operate if both the configured directory doesn't exist and it is running in a container.

I think in some cases, it might be preferred if Radicale created missing directories automatically. For example, if user wants Radicale to create the directory tree on first run.

I think if I update the documentation with precise steps, it might help new users avoid the issues that you have faced.