I mention linux as a skill, as a catch all for the operating system ecosystem, and many applications of it present in the web world. From essential tools like the bash, vi and ssh, to distributions that run on the virtual machines we deploy to, knowledge of the linux environment is essential to web development historically.

I run desktop linux distros for personal development, and have used virtual cloud development servers. Nowdays a developer might get away with only web interfaced tools and IDEs, but an understanding of linux environments is vital for working with the web.