Is it possible to mount an overlay fs inside a (privileged) docker container? At least my intuitive approach, which works fine outside of a container, fails:
> mkdir /tmp/{up,low,work,merged}
> mount -t overlay overlay -o lowerdir=/tmp/low/,upperdir=/tmp/up/,workdir=/tmp/work/ /tmp/merged/
mount: /tmp/merged: wrong fs type, bad option, bad superblock on overlay, missing codepage or helper program, or other error.
Additional information:
Found something that worked! Mounting the workdir and upperdir as tmpfs does the trick for me. Like so:
> mkdir /tmp/overlay
> mkdir /tmp/{low,merged}
> mount -t tmpfs tmpfs /tmp/overlay
> mkdir /tmp/overlay/{up,work}
> mount -t overlay overlay -o lowerdir=/tmp/low/,upperdir=/tmp/overlay/up/,workdir=/tmp/overlay/work/ /tmp/merged/
I'd still be interested in an explanation why creating an overlay w/o tmpfs fails within a docker container?