Error creating default "bridge" network: cannot create network (docker0): conflicts with network (docker0): networks have same bridge name

Question

After stopping docker it refused to start again. It complaint that another bridge called docker0 already exists:

level=warning msg="devmapper: Base device already exists and has filesystem xfs on it. User specified filesystem  will be ignored."
level=info msg="[graphdriver] using prior storage driver \"devicemapper\""
level=info msg="Graph migration to content-addressability took 0.00 seconds"
level=info msg="Firewalld running: false"
level=info msg="Default bridge (docker0) is assigned with an IP address 172.17.0.0/16. Daemon option --bip can be used to set a preferred IP address"
level=fatal msg="Error starting daemon: Error initializing network controller: Error creating default \"bridge\" network: cannot create network fa74b0de61a17ffe68b9a8f7c1cd698692fb56f6151a7898d66a30350ca0085f (docker0): conflicts with network bb9e0aab24dd1f4e61f8e7a46d4801875ade36af79d7d868c9a6ddf55070d4d7 (docker0): networks have same bridge name"
docker.service: Main process exited, code=exited, status=1/FAILURE
Failed to start Docker Application Container Engine.
docker.service: Unit entered failed state.
docker.service: Failed with result 'exit-code'.

Deleting the bridge with ip link del docker0 and then starting docker leads to the same result with another id.

Answer 1

For me I downgraded my OS (Centos Atomic Host in this case) and came across this error message. The docker of the older Centos Atomic was 1.9.1. I did not have any running docker containers or images pulled before running the downgrade.

I simply ran the below and docker was happy again:

sudo rm -rf /var/lib/docker/network
sudo systemctl start docker

More info.

Answer 2

The Problem seems to be in /var/docker/network/ . There are a lot of sockets stored that reference the bridge by its old id. To solve the Problem you can delete all sockets, delete the interface and then start docker but all your container will refuse to work since their sockets are gone. In my case I did not care about my stateless containers anyway so this fixed the problem:

ip link del docker0
rm -rf /var/docker/network/*
mkdir /var/docker/network/files
systemctl start docker
# delete all containers
docker ps -a | cut -d' ' -f 1 | xargs -n 1 echo docker rm  -f
# recreate all containers

Answer 3

It may sound obvious, but you may want to consider rebooting, especially if there was some major system update recently. Worked for me, since I didn't reboot my VM after installing some kernel updates, which probably led to many.network modules being left in an undefined state.