Linux Kernel Installation

Here's a Kernel Korner geared for the new user. Mr. Bandel guides us through the steps of configuring and compiling the kernel.
Building the Kernel

We're now ready to begin building the kernel. There are several options for accomplishing this task:

  • make zImage: makes the basic, compressed kernel and leaves it in the /usr/src/linux/arch/i386/boot directory as zImage.

  • make zlilo: Copies the zImage to the root directory (unless you edited the top-level Makefile) and runs LILO. If you choose to use this option, you'll have to ensure that /etc/lilo.conf is preconfigured.

  • make zdisk: Writes zImage to a floppy disk in /dev/fd0 (the first floppy drive—the a: drive in DOS). You'll need the disk in the drive before you start. You can accomplish the same thing by running make zImage and copying the image to a floppy disk cp /usr/src/linux/arch/i386/boot/zImage /dev/fd0 Note that you'll need to use a high-density disk. The low density 720k disks will reportedly not boot the kernel.

  • make boot: Works just the same as the zImage option.

  • make bzImage: Used for big kernels and operates the same as zImage. You will know if you need this option, because make will fail with a message that the image is too big.

  • make bzdisk: Used for big kernels and operates the same as zdisk. You will know if you need this option, because make will fail with a message that the image is too big.

Other make options are available, but are specialized, and are not covered here. Also, if you need specialized support, such as for a RAM disk or SMP, read the appropriate documentation and edit the Makefile in /usr/src/linux (also called the top-level Makefile) accordingly. Since all the options I discussed above are basically the same as the zImage option, the rest of this article deals with make zImage--it is the easiest way to build the kernel.

For those of you who wish to speed up the process and won't be doing other things (such as configuring other applications), I suggest you look at the man page for make and try out the -j option (perhaps with a limit like 5) and also the -l option.

If you chose modules during the configuration process, you'll want to issue the commands:

make modules
make modules_install

to put the modules in their default location of /lib/modules/2.0.x/, x being the kernel minor number. If you already have this subdirectory and it has subdirectories such as block, net, scsi, cdrom, etc., you may want to remove 2.0.x and everything below it unless you have some proprietary modules installed, in which case don't remove it. When the modules are installed, the subdirectories are created and populated.

You could just as easily have combined the last three commands:

make zImage; make modules; make modules_install

then returned after all the disk churning finished. The ; (semicolon) character separates sequential commands on one line and performs each command in order so that you don't have to wait around just to issue the next command.

Once your kernel is built and your modules installed, we have a few more items to take care of. First, copy your kernel to the root (or /boot/ or /etc/, if you wish):

cp /usr/src/linux/arch/i386/boot/zImage /zImage

You should also copy the /usr/src/linux/System.map file to the same directory as the kernel image. Then change (cd) to the /etc directory to configure LILO. This is a very important step. If we don't install a pointer to the new kernel, it won't boot. Normally, an install kernel is called vmlinuz. Old-time Unix users will recognize the construction of this name. The trailing “z” means the image is compressed. The “v” and “m” also have significance and mean “virtual” and “sticky” respectively and pertain to memory and disk management. I suggest you leave the vmlinuz kernel in place, since you know it works.

Edit the /etc/lilo.conf file to add your new kernel. Use the lines from the image=/vmlinuz line to the next image= line or the end. Duplicate what you see, then change the first line to image=/zImage (assuming your kernel is in the root directory) and choose a different name for the label=. The first image in the file is the default, others will have to be specified on the command line in order to boot them. Save the file and type:

lilo

You will now see the kernel labels, and the first one will have an asterisk. If you don't see the label that you gave your new kernel or LILO terminates with an error, you'll need to redo your work in /etc/lilo.conf (see LILO man pages).

We're almost ready to reboot. At this point, if you know your system will only require one reboot to run properly, you might want to issue the command:

depmod -a 2.0.x

where x is the minor number of the kernel you just built. This command creates the dependencies file some modules need. You'll also want to make sure you don't boot directly into xdm. For Red Hat type systems, this means ensuring the /etc/inittab file doesn't have a default run level of 5, or that you remember to pass LILO the run level at boot time. For Debian systems, you can just type:

mv /etc/init.d/xdm /etc/init.d/xdm.orig
for now and move it back later.

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Its helpful

Abhijeet Bhattacharya's picture

I found your article helpful to start up with my customized version of Kernel which is more efficient now. The most important thing is I am satisfied building my own Linux :-)

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