You may have noticed the term initial ramdisk a few times in this book already. An initial ramdisk is an integral part of both the installation of SUSE and also the day-to-day booting of the operating system. An initial ramdisk is a file containing a compressed image of a small filesystem, and it is uncompressed into memory at boot time so that it can be used as an initial filesystem during the Linux boot process. It takes its name from the fact that the filesystem is uncompressed into an area of memory that the system can use as a disk (with an associated filesystem) during the first stages of the boot process. This Linux filesystem contains startup commands that bootstrap the main SUSE installation by preparing disk devices (by loading device drivers) and making sure your system has enough memory to continue with a SUSE install. Throughout the book we discuss initial ramdisks and their possible uses when booting and using a SUSE system.
Once the boot loader has loaded and executed in memory, you are usually presented with options about what operating system you want to load. This panel typically also enables you to pass additional, optional arguments to the operating system before it loads and initializes.
Figure 4-1 shows the boot screen of the SUSE installer that you saw in Chapter 1. As you can see, you are presented with quite a few options that we discussed before. This is the ISOLINUX boot loader on the SUSE install media.
Figure 4-2 shows the SUSE boot loader that is installed by default after successfully installing SUSE. This screen provides fewer, and different, options than those shown in Figure 4-1 because they refer only to the installed operating system and a failsafe Linux system (that you can use in case your main SUSE boot configuration is corrupted).
After SUSE has been installed, selecting the default boot option, Linux will load the kernel and the initial ramdisk in memory. If you do not specify anything at this menu, the system automatically boots the default choice after ten seconds. The processor then jumps to the start of the kernel in memory and executes it. The execution of the kernel is usually very quick, within five seconds. After the kernel has loaded, you will see the initial ramdisk being mounted, and the small Linux distribution takes over and loads any drivers that are needed to load your Linux installation from the disk. SUSE hides much of the boot process behind a graphical screen that simply displays a progress bar. You can press F2 at any time during kernel loading and initialization to see detailed status messages that explain exactly what the system is doing.
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