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Why Does Changing My Hostname Cause `sudo` to Hang on Ubuntu?

September 4, 2025 5 answers
Asked by CuriousCat42
I recently ran into a curious issue on my Ubuntu system where using `sudo` would hang for several minutes after my VPN's kill-switch kicked in. I discovered that `sudo` tries to resolve the hostname to the system's Fully Qualified Domain Name (FQDN) by default on Ubuntu, since it's compiled with the `--with-fqdn` flag. At some point, I altered my system hostname, but `etc/hosts` didn't get updated automatically, leading to a mismatch with the new hostname. When my VPN's kill-switch blocked DNS requests, the hostname resolution failed, resulting in `sudo` hanging while it waited for a timeout. I'm looking for thoughts on this situation: - Should tools like `hostnamectl` or the Settings app automatically update `etc/hosts` when the hostname changes, or at least notify the user? - Is it wise for `sudo` to have FQDN resolution enabled by default, as it is on Ubuntu? It seems like it introduces an avoidable point of failure for such an essential tool. For instance, Fedora doesn't activate this option by default, and Debian is thinking about removing it as well.
hostname sudo system administration System Operations troubleshooting ubuntu vpn

Answers

SystemMaster99
Changing a hostname on an established server isn’t usually a good idea. It can lead to all sorts of complications like this. Typically, it's better to rebuild the system than to just change the hostname.
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DNS_Wizard83
It sounds like a classic DNS problem! I’ve had similar experiences, especially when logging in via SSH with faulty DNS. Always a headache.
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WorkstationWarned
Exactly! Plus, not every system is a server; some are just workstations. It might not be as critical to change those.
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TechieGizmo9
That’s quite the issue! If you didn’t update `etc/hostname`, what exactly did you change? Were you modifying the static entries in `etc/hosts` or messing with DNS settings?
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RebootAdviser37
I agree with rebuilding, but I get that it’s not feasible for everyone. Usually, changing a DNS entry is all that’s needed rather than a hostname change.
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