Description Sönke Schwardt-Krummrich 2021-04-14 09:43:55 CEST

UCS+docker on btrfs seems to work as of UCS 5.0, although I haven't tested it extensively yet. The important thing is to run the following before installing the first app:

# ucr set docker/daemon/default/json='{ "storage-driver": "overlay2" }'
# systemctl restart docker.service

If the UCR variable is not set, docker automatically uses the storage-driver "btrfs", which then currently causes problems with our internals from AppCenter (the code looks for the "MergedDir" of overlayfs, which does not exist with btrfs).

Since overlay2 on btrfs should now work with the kernel from UCS 5.0, one could consider setting the storage driver in general and removing the warning in the installer in UCS 5.0-1.
See https://btrfs.wiki.kernel.org/index.php/Changelog#By_feature:
→ Kernel 4.7: Add support for RENAME_EXCHANGE and RENAME_WHITEOUT to renameat2 syscall. This also means that overlayfs is now supported on top of btrfs. 
→ Kernel 4.15: Overlayfs can now use btrfs as the lower filesystem. 
→ UCS 5.0 uses kernel 4.19

We should consider setting the storage-driver permanently via UCR to "overlay2".

Implementing btrfs support in app center would also be a solution, but would also increase complexity.

If this works, the btrfs warning within the debian installer has to be removed, too.