FIX: "Hash sum mismatch" on Linux Mint update

OK, here is the scenario.

I have a Linux Mint machine (maya) that has not been booted for some time.

I started it up and decided to do some housekeeping as a prelude to upgrading it to 'Nadia'

The first thing I did was do an apt-get update which failed with "hash sum mismatch" when updating the Mint list (Sorry, I didn't keep a copy of the full error)

Another machine on my LAN is already on Nadia and it apt-get updates fine.

I use apt-cacher-ng, so I disabled this and tried update again. This worked, which led me to believe there was some corrupt file in the cache somewhere. I spent hours trying to nail this and even did apt-get purge apt-cacher-ng followed by a re-install.

None of this worked.

Eventually something twigged in my brain, and I wondered if there was a compatibility problem with the version of apt on this machine. As I said, it's been some time since I updated.

Here is  what I did;

1) Edited sources.list and commented out the single Mint line, leaving just the ubuntu repositories in place. These were updated from 'precise' to 'quantal'.

2) Did an apt-get update, this worked without errors.

3) Upgrade apt (apt-get install apt) this installed about three new files.

4) Edited sources.list again, removing comment from the Mint line and changed it from 'maya' to 'nadia' while I was there.

5) Another apt-get update and this time there were no errors.

From there everything worked as expected and no more hash sum mismatches!

Purge Your System Of Mono

Updated 18/6/2012 for Mint 13 "Maya" / Ubuntu 12.04 "Precise"

If you are not overly happy with having a bastard child of Microsoft installed on your systems and the potential patent issues that may arise from its use then this simple one liner will purge your system of mono and anything that depends on it.

Make sure you read the list of packages to be removed that the apt-get command provides before you go ahead and do it.

sudo apt-get purge mono-4.0-gac

This will remove the following from your system.

The following packages will be REMOVED:
  banshee* libappindicator0.1-cil* libdbus-glib1.0-cil* libdbus1.0-cil* libgconf2.0-cil* libgdata1.9-cil*
  libgkeyfile1.0-cil* libglib2.0-cil* libgmime2.6-cil* libgtk-sharp-beans-cil* libgtk2.0-cil* libgudev1.0-cil*
  liblaunchpad-integration1.0-cil* libmono-addins-gui0.2-cil* libmono-addins0.2-cil* libmono-cairo4.0-cil*
  libmono-corlib4.0-cil* libmono-i18n-west4.0-cil* libmono-i18n4.0-cil* libmono-posix4.0-cil*
  libmono-security4.0-cil* libmono-sharpzip4.84-cil* libmono-system-configuration4.0-cil*
  libmono-system-core4.0-cil* libmono-system-drawing4.0-cil* libmono-system-security4.0-cil*
  libmono-system-xml4.0-cil* libmono-system4.0-cil* libmono-zeroconf1.0-cil* libnotify0.4-cil* libtaglib2.0-cil*
  mint-meta-cinnamon-dvd* mono-4.0-gac* mono-gac* mono-runtime* tomboy*
0 upgraded, 0 newly installed, 36 to remove and 0 not upgraded.
After this operation, 34.3 MB disk space will be freed.

If you are happy to lose that stuff, in particular the Banshee audio player then go ahead hit "y" to nuke Mono once and for all*

* Actually, next time you do a dist-upgrade you are likely to have the mono infection return to your system. In such cases just reapply this treatment.