About the Unix Boot Process
Bootstrapping is the full name for the process of bringing a computer system to life and making it ready for use. The name comes from the fact that a computer needs its operating system to be able to do anything, but it must also get the operating system started all on its own, without having any of the services normally provided by the operating system to do so. Hence, it must “pull itself up by its own bootstraps.” Booting is short for bootstrapping, and this is the term I’ll use.[1]
The basic boot process is very similar for all Unix systems, although the mechanisms used to accomplish it vary quite a bit from system to system. These mechanisms depend on both the physical hardware and the operating system type (System V or BSD). The boot process can be initiated automatically or manually, and it can begin when the computer is powered on (a cold boot ) or as a result of a reboot command from a running system (a warm boot or restart).
The normal Unix boot process has these main phases:
Basic hardware detection (memory, disk, keyboard, mouse, and the like).
Executing the firmware system initialization program (happens automatically).
Locating and running the initial boot program (by the firmware boot program), usually from a predetermined location on disk. This program may perform additional hardware checks prior to loading the kernel.
Locating and starting the Unix kernel (by the first-stage boot program). The kernel image file to execute may be determined ...
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