2.1 Boot Process

When a computer is powered on and has performed its power-on self test (POST), BIOS routines are executed that recognize and initialize hardware components such as hard disk controllers, hard disks, network adapters, etc.

Afterwards control of the boot process is passed to the boot loader, which is located on a bootable device (for example, CD-ROM, hard disk, network (PXE)). The boot loader starts a kernel and optionally an initial RAM disk (initrd). Up to SLES 11 the default boot loader has been grub which has been replaced with grub2 in SLES 12 and later.

Most operating systems accept custom boot options to pass instructions to the kernel or to the initrd. These instructions can be used to influence hardware initialization or which functions to execute. One application of custom boot options is to initiate an automated installation.