It was patch day for the test environment, the group of servers dedicated to testing locally developed code before it is pushed into QA, and then into production. Patches for RedHat Enterprise Linux are applied using "yum update" in our setup, keeping it simple. Things were going well, no conflicts, no problems with our applications after the patches were applied. Then, one of the server's yum processes died with an error--a very familiar error. Yum was trying to install a patch that depended on a certain library being at a certain level. Our library in question was higher than the level required. That library had been updated prior to patch day, so rolling it back would break whatever package installed it. I was immediately flashed back ten years...dependency hell.