Convert a RHEL box to Scientific Linux with no downtime

I saw the following tweet today.

I was faced with the same task a couple years ago and discovered that it’s actually a lot simpler than you’d guess. (It helps that 99(.44)% of the code between the same versions of Red Hat Enterprise Linux, Scientific Linux, and CentOS is identical.) After determining the minimum number of packages I needed to remove, replace, or install, and in what order to do everything, I came up with the procedure detailed below. Once I tested it on a few boxes and was satisfied with the results, I handed the job off to puppet and it took care of converting the rest of my RHEL boxen to SL. (If you’re interested in seeing the puppet manifest I used to do this, let me know in the comments.)

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