• This is a bug report
• This is a feature request
• I searched existing issues before opening this one

Expected behavior

Proceed start

Actual behavior

Aborted start

Steps to reproduce the behavior

I ran Docker in systemd-nspawn "machine" — in particular to avoid cluttering of the netfilter's rule set. Generally it worked until recent update.
Output of docker version:

Client: Docker Engine - Community
 Version:           19.03.11
 API version:       1.40
 Go version:        go1.13.10
 Git commit:        42e35e61f3
 Built:             Mon Jun  1 09:12:22 2020
 OS/Arch:           linux/amd64
 Experimental:      false
Cannot connect to the Docker daemon at unix:///var/run/docker.sock. Is the docker daemon running?

Output of docker info:
— not applicable, since system service is down

The whole error message:

dockerd[…]: failed to start daemon: Error initializing network controller: Error creating default "bridge" network: libnetwork: Unable to disable IPv6 router advertisement: open /proc/sys/net/ipv6/conf/docker0/accept_ra: read-only file system