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18.04 with latest updates.

I am trying to modify my /etc/hosts file so I can access my local server via its hostname.
I make the change with sudo nano /etc/hosts, and it sticks fine for the current session. However, after rebooting my system or suspending it, the file reverts itself back to the state it was in before I edited it.
I have attempted to edit using both the terminal in a graphical session as well as from a tty prompt on a fresh boot with no avail.
This has only started happening since a new router was installed in my homes network, however I cannot see why that would cause this issue. 

$ ls -al /etc/hosts   
-rw-r--r-- 1 root root 254 Jan 20 17:03 /etc/hosts
Hamish W
  • 341

1 Answers1

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The file is overwritten by systemd-resolved.service, among other files:

systemd-resolved synthesizes DNS resource records (RRs) for the following cases:

  • The local, configured hostname is resolved to all locally configured IP addresses ordered by their scope, or — if none are configured — the IPv4 address 127.0.0.2 (which is on the local loopback) and the IPv6 address ::1 (which is the local host).

  • 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.

  • The hostname "_gateway" is resolved to all current default routing gateway addresses, ordered by their metric. This assigns a stable hostname to the current gateway, useful for referencing it independently of the current network configuration state.

  • The mappings defined in /etc/hosts are resolved to their configured addresses and back, but they will not affect lookups for non-address types (like MX).

According to documentation for /etc/systemd/resolved.conf and the related post, you can edit /etc/systemd/resolved.conf to have specific domain resolved by your local DNS sever (on Ubuntu you have dnsmasq, example), or add ReadEtcHosts= to let the service actually use the file.

You can also disable the service. See How to disable systemd-resolved in Ubuntu?

According to a Fedora forum thread the issue could also relate to Network Manager service. For Ubuntu servers, cloud-init could also be the cause of the issue according to the bug report on launchpad

Sergiy Kolodyazhnyy
  • 107,582