[Bug] DNS resolution not working in a rootful systemd container without unshare-netns option.

[kerneis-anssi]

[Bug] DNS resolution not working in a rootful systemd container without unshare-netns option.

[89luca89]

Hi @kerneis-anssi thanks for the issue

I was not able to reproduce this issue

[kerneis-anssi]

I found the following in the container's log (journalctl -b0):

Feb 02 12:16:31 fedora-tb.fedora systemd-resolved[492]: LLMNR-IPv4(UDP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.
Feb 02 12:16:31 fedora-tb.fedora systemd-resolved[492]: LLMNR-IPv4(TCP): There appears to be another LLMNR responder running, or previously systemd-resolved crashed with some outstanding transfers.
Feb 02 12:16:31 fedora-tb.fedora systemd-resolved[492]: LLMNR-IPv4(TCP): Failed to bind socket: Address already in use
Feb 02 12:16:31 fedora-tb.fedora systemd-resolved[492]: Another LLMNR responder prohibits binding the socket to the same port. Turning off LLMNR support.
Feb 02 12:16:31 fedora-tb.fedora systemd-resolved[492]: Another process is already listening on TCP socket 127.0.0.53:53.
Feb 02 12:16:31 fedora-tb.fedora systemd-resolved[492]: Turning off local DNS stub support.

The following made name resolution work again (from the container):

sudo systemctl stop systemd-resolved
sudo systemctl disable systemd-resolved

I have no clue why, I hope others will find this useful.

[89luca89]

Nice find, I'll transform this in a discussion for future reference for other people 👍