When you are working on your own as a developer you get exposed to many aspect of the business. You don't really draw border lines. As a web developer you blend in all kind of technology and you consider it all just web development. When you work in a big or established company it is a little different. They don't need full stack developers. They have a person or a group of people that work in just one thing; DBA or Unix for example. If you do this for a while you can become an expert in your field, but lose something in other areas.
After having a regular job for a while in an established company I have started to forget what a full stack developer does. In the beginning I was working on multiple projects and was taking care of backend and frontend, but now I spent months just working on one side of a project. Just recently I have decided to tackle a new project with some friends and I realized there is so much I have forgotten.
Things I used to know and am now relearning.
I haven't created a deployment procedure from scratch for ages, apparently you need one.
Setting up permissions on a linux box is fairly easy when you do it regularly, but chown and chmod? After a while it sounds like clown to me.
You actually do need to create users on for you SQL database. You don't just use the root user.
modrewrite is not enabled by default on an Apache server.
If you don't use CSS you lose it.
Iptables rules sounds like gibberish to me.
These are just a few of the things where I was stuck. Luckily the web is full of information to help, sometimes a little too much.
Here is one spot that help me setup all the basics on my Linux box. It will be a long way before I am proficient in being a full stack developer again, but specializing is not suck a bad alternative, cause I can cook up something awesome in no time.