Properly evaluate Linux server to Unix server migrations before undertaking any projects, and know when such a migration is a bad idea for a customer' shop. This collection of tip excerpts from our sister site SearchOpenSource.com will get you started.
Unix-to-Linux migration considerations
Part 1: Unix-to-Linux migration benefits
Part 2: Make a Unix-to-Linux migration for the right reasons
Part 3: Migrate to Linux when old systems become expensive
Part 4: Wrong reasons for Linux migration