Comment 37 for bug 1996909

And I do not believe this is a regression in docker.io because the daemon tries to create a directory to store the image and the filesystem is read-only. Outside the lxd container the same command works fine. The error is in the commit message here:

https://github.com/tianon/debian-docker/commit/e44fd120bbd0381a08baef2cbac789b82635af2d

But I do not know whether the behavior change comes from lxd or linux. It will require further investigation.