Ubuntu apt Hash Sum Mismatch

So today I was attempting to change some things up on one of our servers and running a normal SaltStack highstate was timing out and causing the minion process to basically just hang. After some investigation looking over the logs in /var/log/salt/minion it was obvious the issue was with apt-get updating it’s package listings.

But that’s strange, this box is on Digital Ocean and they have their own local mirrors. Turns out it’s a fairly common scenario with Ubuntu + mirrors + badly configured proxies. If you’re seeing things like this in your logs:

W: Failed to fetch Hash Sum mismatch
Failed to fetch Hash Sum mismatch
: Failed to fetch Hash Sum mismatch
E: Some index files failed to download. They have been ignored, or old ones used instead.
E: Couldn't rebuild package cache

There is a pretty easy fix. You just need to clear our your existing apt source caches and re-update like this:

rm /var/lib/apt/lists/*
rm /var/lib/apt/lists/partial/*
apt-get update

This totally solved the issue for me. Not only unlocking/unsticking apt, but also making subsequent apt calls a touch faster. Hope this helps someone else!

Posted 04 December 2014

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Frank Wiles

Founder and President of REVSYS and current President of the Django Software Foundation. Web/Ops maven specializing in scaling complex web applications. Want to reach out? Contact me here or use the social links below.