I'm trying to add a search line to /etc/resolv.conf

I've added it directly, as an append command in /etc/dhcp/dhclient.conf and as a nameservers block in /etc/netplan/50-cloud-init.yaml.

After roughly an hour, the dhcp and netplan files are intact, but resolv.conf has reverted to not having my search.

I haven't changed /etc/network/interfaces because it says "ifupdown has been replaced by netplan(5) on this system."

Any thoughts on what might be overwriting /etc/resolv.conf besides those two things?

This is ubuntu 18.04 on EC2.

/etc/resolv.conf is a dynamic configuration file generated by the resolvconf process:

$ head /etc/resolv.conf
# Dynamic resolv.conf(5) file for glibc resolver(3) generated by resolvconf(8)
# DO NOT EDIT THIS FILE BY HAND -- YOUR CHANGES WILL BE OVERWRITTEN
nameserver 127.0.1.1

This file is generated from the files located under /etc/resolvconf/resolv.conf.d/. To write your own changes to the contents of the /etc/resolv.conf simply add the lines that you would usually add to the resolv.conf file instead to the /etc/resolvconf/resolv.conf.d/base file.

There is a complex fight to get control over the resolv.conf file, it is an old fight.

Contenders that try to write a resolv.conf are resolvconf, dhcp, interfaces, network manager and recently systemd-resolved. Other programs also may use resolv.conf, like dnsmasq.

Thus, a simple solution doesn't work in all cases.

• If you have the resolvconf program installed (which main goal is to take ownership of the resolv.conf file) then: un-install it.




• If your system use DHCP to get a working IP (most probably you do), every hour or so (depending on system configuration) the IP gets renewed, that re-writes resolv.conf. Detect if this is the source of the problem.




• The file /etc/interfaces may be used to change the resolv.conf configuration. Find out if it is (and erase it).




• Network Manager could be configured to change what resolv.conf does. Detect (and erase) if it is doing so.




• Systemd- resoved may be configured to take control of resolv.conf via a sym-link. Remove the link if it exists.




• Some recomend to make resolv.conf not modifiable (I believe that is more a problem than a solution). Remove it if it exists.

After you have removed all the above: decide who should keep control of resolv.conf file understanding that DHCP must update the file when a new DHCP lease is obtained.

Ask for more help if needed.

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