[chr15p]

if you have 100 machines you need to install 100 new OS's which just by itself is a bunch of work.

The actual install of linux is generally pretty straight forward but to do it minimum downtime you need spare boxes to build with the new distro (preferably 1 for each old box, but you can get away with less, its just takes more time), install your software on, and then test. You also need sysadmins and testers to do the work, and developers to fix any issues (normally around library versions etc). Then you have the risk that something was missed in the install & testing and causes issues in prod a new distro will not be 100% bug compatible with your old one so you will find problems.

And thats assuming you have the skills to install the new distro, how to set it up as required, how to reinstall the software (its amazing how much in house software doesn't have install docs or even source code), and the skills to run it 24/7. If not factor in training and self-learning time for everyone.

Its all doable, but its probably months of work and a bunch of risk just to get back to where you were on a new distro, which makes no difference to your customers at all.

Theres a reason companies tend not to switch very often.