[Gllug] Back-out plans on Debian/Redhat?

[Khusro Jaleel]

Hi, I was reading

"The Practice of System and Network Administration"
http://www.amazon.co.uk/Practice-System-Network-Administration/dp/0201702711

and the chapter on Change Management states that you must have a
back-out plan in case of problems when you are making major updates to
a system.

What I'm not sure about is for example, if I have a critical
Debian-based webserver which has a lot of updates due (Apache, Mysql,
Kernel, Libc, etc) how do I implement a back-out plan for
dist-upgrades in case there are problems?

In the case of Apache, would a simple "apt-get install
previous-version.deb" work? In the case of MySQL, I know I should do a
DB dump before and later on I should be able to re-install the old
version of the package and re-import the dump. In both cases I will
have to make sure to save the previous version's .deb files somewhere
so I could go back I suppose.

Is that really all there is to backing out or is there more? Also,
what about a Redhat / CentOS system, can you just install the older
RPMS on those and things will be fine?
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