Upgrade Centos 6.8 to 7

Hi,

In my experience, doing a major version upgrades is inadvisable. The reason being that there are significant changes done between major releases. Attempting to upgrade from 6 to 7 can easily break something, and more importantly will often leave artefacts from the old version around which may either cause conflicts or take up unnecessary space and resources. It just gets messy.

When I do (and am actively doing) upgrades from 6 to 7, I'll simply setup a brand new machine with the newer version, and migrate sites over either one-by-one or in bulk. This offers a cleaner transition, though will sometimes take a bit longer to do correctly. However, with proper planning and scheduling, you can either minimize or nearly eliminate any noticeable downtime. For instance, we schedule migrations during the early AM hours.

If you require assistance planning, and/or executing a seamless migration, please feel free to drop me a line. I currently run a decent sized cluster and have been shifting from CentOS 6 to 7 over the past year in various steps. No customer has ever noticed the moves until I'm like "you've been moved" in which they become delighted to see any new features, or improvements as a result of.

Peter is correct. While its possible it is just a bad idea. Even Windows users (where you can actually do an in place upgrade) tend to wipe everything and do a full reinstall between major versions (like 7 to 10).

There are so many new things that chances of having old RPM and packages from the old system in place can be a major pain in the butt in the future. Its just not worth the risk. Its complicated and messy. The best approach is just to spin a new CentOS 7 machine, and migrate your data manually.