Linux Foundationals: From Silicon to Userspace - The Boot and Init Chain

Every Linux system you have ever logged into went through the same sequence a few seconds before you got a prompt. Firmware found a bootloader, the bootloader found a kernel, the kernel found a root filesystem, and something called PID 1 turned all of that into a running system. Most of the time nobody looks at this chain. It only gets attention when it breaks, and then it gets a lot of attention at once. This is the first article in the Linux Foundationals series, the Linux counterpart to FreeBSD Foundationals. The reference system throughout is Fedora (45 at the time of writing), but nearly everything here applies unchanged to RHEL 9 and 10, CentOS Stream and the other members of the family. The series follows the order in which a system actually comes alive: this part gets us from power-on to a running systemd, and the following parts build on top of that. By the end of this article you’ll know what every file on the EFI System Partition is for, what Secure Boot actually verifies…