I'm using the datastax version of cassandra and installed it with the command:
apt-get install cassandra=1.1.9
and, once you do that, apt-get is good about not upgrading any further at all.
But this morning I wasted several hours with hung software on my development machine unto I spotted that "Ubuntu software updater" had upgraded my cassandra to 1.2.x! AGAIN! ARGH!
After some research this does the trick.
1. create a file
2. in it add the lines:
Package: cassandra Pin: version 1.1.* Pin-priority: 1000
3. apt-get update
From now on upgrades should only get the 1.1.x versions (it's now at 1.1.11). You can check this with:
apt-cache policy cassandra
This works fine for the "user friendly" updater too.