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Accepted
Ryan
Asked: 2023-02-08 19:11:02 +0800 CST

Ubuntu 22.04.1 nameservers keep getting overwritten

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I upgraded from Ubuntu 20.04 to 22.04.1 yesterday.

Now, whenever I toggle wifi back on (from temporarily being off), I have no internet access.

I checked:

ls -lah /etc/resolv.conf
lrwxrwxrwx 1 root root 28 Feb  7 14:24 /etc/resolv.conf -> /opt/valet-linux/resolv.conf 
cat /etc/resolv.conf

search attlocal.net
nameserver 127.0.0.1

Then I makes changes:

sudo vim /opt/valet-linux/resolv.conf
cat /opt/valet-linux/resolv.conf

nameserver 8.8.8.8

And then the internet works again.

But if I toggle Wi-Fi off and then back on, that file gets reset again.

I've already tried:

DNS

and:

cat /etc/netplan/01-network-manager-all.yaml 
# Let NetworkManager manage all devices on this system
network:
  version: 2
  renderer: NetworkManager
  ethernets:
    eth0:
      nameservers:
        addresses:
        - 8.8.8.8
        - 8.8.4.4

from https://linuxize.com/post/how-to-set-dns-nameservers-on-ubuntu-18-04/ and countless posts on AskUbuntu and StackOverflow.

I've also tried:

cat /etc/dhcp/dhclient.conf
...
# https://stackoverflow.com/a/48652642/470749
supersede domain-name-servers 8.8.8.8;

from https://stackoverflow.com/a/48652642/470749.

Nothing works. I'm losing my patience with Ubuntu.

What have I done to get myself in this mess? Thanks.

networking

3 Answers

  1. There can be only one entry that writes/managed /etc/resolv.conf.

    For example, NetworkManager or the human administrator. There is also resolvconf, which is a tool that accepts multiple sources for DNS configuration, and then merges them into one /etc/resolv.conf.

    By default, NetworkManager runs with [main].rc-manager=symlink setting. See man NetworkManager.conf. Unless you changed that configuration, NetworkManager won't touch the file. Read also about [main].dns= setting.

    In general, you need to make up your mind about what should configure it, and then configure all related software to agree on that. Since NetworkManager by default already leaves the file alone, if it's a symlink, you don't need to tell NetworkManager to stay off.

    If you use one of the GUIs to configure DNS, then those GUIs actually configure the profile in NetworkManager. That only works, if NetworkManager is instructed to write /etc/resolv.conf

    Commonly systemd-resolved is used. Resolved doesn't write /etc/resolv.conf, but it can consume it as input. If you use that, usually /etc/resolv.conf should be just a symlink as documented in /ETC/RESOLV.CONF section in man systemd-resolved. In that case, NetworkManager can push it's DNS configuration to systemd-resolved. Run resolvectl to see that configuration in systemd-resolved.

    Changing /etc/dhcp/dhclient.conf seems quite wrong. Especially, if you use NetworkManager which by default doesn't use dhclient. In any case, injecting the DNS setting in the DHCP client is not right. In NetworkManager, you configure DNS by setting it in NetworkManager's connection profiles (+ setup your system and NetworkManager to do the right thing with those settings).

    There is not one answer, because it depends on how exactly you want to set up your system. Commonly you would stick to what your distro provides you with. Understand what your distro is setup to do, and use the appropriate mechanisms in that case. Who created /etc/resolv.conf as a symlink, and why did it do that? (Neither NetworkManager nor systemd-resolved would do that).

    • 2
  2. Best Answer

    Since I hadn't used valet-linux for years, I'd completely forgotten about it and didn't even recognize the name.

    Thanks to @chili555 for the comment pointing out what I didn't even notice as unusual.

    I finally found https://github.com/cpriego/valet-linux/issues/115#issuecomment-1406379951, which in combination with commands like the following (inspired by https://cpriego.github.io/valet-linux/#uninstalling), seemed to work:

    composer global remove cpriego/valet-linux
sudo rm -rf /opt/valet-linux/
sudo systemctl revert systemd-resolved
sudo systemctl restart systemd-resolved
sudo apt-get remove dnsmasq
sudo rm /etc/resolv.conf
sudo ln -s /run/resolvconf/resolv.conf /etc/resolv.conf
sudo systemctl stop valet-dns
sudo systemctl disable valet-dns
sudo rm /etc/systemd/system/valet-dns.service
sudo systemctl daemon-reload
sudo systemctl reset-failed
sudo systemctl restart NetworkManager
    • 1

  3. Use systemd-resolve instead of manually editing resolve.conf.

    for example:

    sudo systemd-resolve --interface wlp2s0 --set-dns 192.168.88.22 --set-domain yourdomain.local
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