Linux

Every running program on Linux is a process with its own PID (process ID). Knowing how to inspect and control processes is a fundamental sysadmin skill.

Debian-based distributions (Ubuntu, Linux Mint, Raspberry Pi OS) use apt to install, update, and remove software packages from curated repositories.

Linux uses a permission model based on read, write, and execute rights for three classes of user: owner, group, and others. Understanding it is essential for system security.

Bash (Bourne Again SHell) is the default shell on most Linux distributions. Mastering a handful of commands gets you productive immediately.

Linux is a free and open-source operating system kernel first released by Linus Torvalds in 1991. Today it powers everything from smartphones to supercomputers.