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foobar
Asked: 2019-03-12 23:10:24 +0800 CST

DNS resolving of localhost subdomains stopped working after resolvconf update

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For years I'm using Ubuntu (currently on 18.10) to develop PHP applications on domains like foo.bar.localhost for local testing. These domains were resolved to 127.0.0.1 and handled by Apache 2.4. This always worked. The line 127.0.0.1 localhost is in my /etc/hosts like it always was.

Today morning I turned my device on and this did not work anymore. ping localhost is still working, but ping foo.bar.localhost is not (it still was working yesterday). Surprisingly Chromium is still resolving foo.bar.localhost, I assume it's not using the OS for DNS resolving. But I'm mainly using Firefox, which also stopped resolving localhost subdomains.

I didn't change any system-related settings yesterday, but I remember some package updates from yesterday, so I assume there were some changes to some network-related things. Is there any way to get dpgk to list install/update dates so that I can find out the exact packages that were updated?

What settings could I check to make resolving subdomains work again system-wide? Are there any known bugs?

Additional information: In /var/log/dpkg.log I found a recent entry upgrade resolvconf:all 1.79ubuntu10 1.79ubuntu10.18.10.1 which sounds relevant. This and the following subsequent lines are the only lines containing the term "resolv" (found with cat /var/log/dpkg.log | grep resolv). So, in the last hours this DNS-relevant package was updated.

Another information: the manual man systemd-resolved has the following line:

The hostnames "localhost" and "localhost.localdomain" (as well as any hostname ending in ".localhost" or ".localhost.localdomain") are resolved to the IP addresses 127.0.0.1 and ::1.

So this well-defined behaviour stopped working. I also can not remember changing anything related to this lowlevel DNS stuff myself.

The exact message when doing ping foo.bar.localhost is

ping: foo.bar.localhost: Name or service not known

Apparently the only bug "fixed" in the new version of resolvconf was this: https://bugs.launchpad.net/ubuntu/+source/systemd/+bug/1817903 which is related to local resolving.

networking browser localhost resolvconf web-development

1 Answers

  1. Best Answer

    The problem was having resolveconf installed at all alongside systemd-resolved. I removed it by apt-get purge resolvconf with root rights. Then everything worked again.

    I assume having both installed was a left-over from some previous major version update between Ubuntu releases, which now triggered this strange behaviour.

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