Yes, thats fine and dandy, but you also have to look into the future. The rate at which technology is progressing, we are not going to have to have a need for unix/linux, therefore putting your job out of business.
Just remember, you need to pick something that is going to be needed in the next 30 years or more. There will always be crime, therefore, you will always need law enforcement officers, and people are always going to get sick, so there will always be a need for doctors and nurses.