Fixing a Broken DNS in Linux Mint 13

Clearly I just have to start remembering more IP addresses

So last week I needed to go abroad (to CERN as it happens) and when I got there, my Mint 13 running laptop decided to throw a paddy and stop talking to the DNS. I could ping usual Google IPs (8.8.8.8 for example) but DNS just hung despite being reported to correctly (and pingable) in the Network Settings. Having a look at my resolv.conf, I could see that my DNS settings were set to my Uni one. I couldn't remember if these were put in automatically by the ethernet connection in my office or I'd just dumped that there randomly for some reason, but tellingly, these DNSs were NOT pingable (I guess they had fallen over or something).

So, I thought, not a problem - just change the DNSs to Google's and all should be well. Except it wasn't. The laptop was still refusing to talk to anyone by name. Luckily, my phone was not having these troubles and some frantic searching led me to the following Blog. It appears someone in Ubuntu land was trying to be clever and started using dnsmasq instead of resolv.conf. I don't know why this was done and really can't be bothered to find out, but in this occasion it meant I could not find whatever black magic was needed to force the Google DNS to be used.

By *mostly* following the blog, I discovered the following worked like a charm to get control of the DNS back to resolv.conf where (in my humble - and probably naive - opinion) it should still reside. First up, (and be aware, this should all be done under su/root), stop Mint from using dnsmasq by going to:

/etc/NetworkManager/NetworkManager.conf

And commenting out the dns line:

#dns=dnsmasq

Next, get resolvconf to sort out it's links and bring back resolv.conf:

dpkg-reconfigure resolvconf

Just to be sure, do a few more housekeeping bits and pieces and follow up with a restart:

resolvconf --create-runtime-directories
resolvconf --enable-updates
reboot

And now you should be able to edit /etc/resolv.conf as usual and have Mint listen to you. Note that you may want to also change:

/etc/resolvconf/resolv.conf.d/original

for a more permanent setting as I believe on restart resolvconf will recreate the resolv.conf with this. 

Last thing to note: While messing around, I tried to select 'Automatic (DHCP) addresses only' under IPv4 Settings for the wireless I was using. THIS WAS A BAD IDEA! It stopped the above working for other reasons I didn't understand. I plan to revisit all this at some point to try to better understand how DNS is handled in Mint/Ubuntu as I'm sure there was probably a better way around this...