Wednesday, August 20, 2008

How SUSU Linux Loading the Kernel

When GRUB hands over the process to the SUSE Linux kernel, it leaves the scene. The kernel now takes charge, putting up the message Uncompressing Linux...; it is present and available to you until you shut down the system. While the kernel boots, SUSE Linux puts up a nice blue wallpaper to hide all the boring text that scrolls by as the kernel initializes first your peripheral hardware, then the hard drive and attending file systems, followed by the serial ports. Press the Esc key to watch the boot process unfold.

As a user, or even as an administrator, you don't have much direct interaction with the Linux kernel. You run applications, which occasionally interact with the kernel to get things done. In the kernel's view of things, an application is simply a process, one of many it deals with. The father of all processes, which the kernel loads soon after the kernel itself loads, is called init, located in the /sbin directory. The rest of the boot process (and later, the shutdown process) is really handled by init, not the kernel. All other processes are started by init or one of its child processes. Init is centrally configured by the /etc/inittab file.

After activating the serial ports, the kernel runs a series of boot scripts, located at /etc/rc.d/boot.d, which activates (and, if required, mounts) still more devices and local file systems.

Then boot.clock sets up the system clock, ldconfig identifies the current time zone, and local networking interfaces are turned on via boot.sysctrl, boot.localnet (for the loopback interface), and boot.isapnp.

Finally, the kernel's System Boot Control declares

The system has been set up and runs /etc/init.d/boot.local. This program invokes the appropriate runlevel for the system. There is much more on runlevels in the next section, but a standard networked desktop will launch Runlevel 5 as it hits the home stretch of the boot process.

At Runlevel 5, networking services are started and various other services and the system logs come online. The sound driver, keyboard maps, CUPS printer interfaces, mail transfer agent, and xinetd Internet services come next.

Finally, the kernel starts the X Window System and the display manager (KDM by default) that allows the user to log in. Logging in loads the desired desktop, and you're done.

To closely examine your most recent boot process, open /var/log/boot.msg in a text editor, or open the YaST View Startup Log module from the Misc page.

Source of Information : SUSE Linux 10 Unleashed

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