Last update: October 7, 2001

Secrets I learned... about building a new kernel
Credits
Other sources
  • jgo.local.net/LinuxGuide (See "System: Compiling a New Kernel")
  • README in the top level of an untarred kernel tar ball. There's also a Documentation tree as well

Why build a new kernel?

Sometime after you've completed your Linux installation, perhaps much later, you may have need to install a new kernel. Now is the time to plan for that. And the best way to plan is to go through the exercise.

In the normal course of creating a new kernel, a .config is created that contains the options (and there are a lot of them) that are being used.

But it is often the case that an initial distribution install does not record how your newly installed kernel was built. ie: It did not provide a .config file reflecting the build parameters that were used. So, for that reason if none other, we'll make a new kernel now.

When the time comes that you need to create a new kernel, odds are that you'll want the new kernel to be configured in much the same way as the old one.

This discussion deals with the creation of a new kernel. At this time, the only reason you may wish to create a new kernel is to create a .config file. (By the way, you may choose to save the config file by any name you want; it doesn't have to be .config)

Before building a new kernel

Do you have a boot diskette? If not, make one...
      # fdformat /dev/fd0H1440
      #

      # uname -r
      2.2.16-3
      # mkbootdisk --device /dev/fd0H1440 2.2.16-3

...and test it!
The /dev/fd mentioned here may not be the one for you.
The storage media may not be in sufficiently good a shape.

Building a new kernel

Assume your new kernel source is in a file such as linux-2.4.0.tar.gz

  • Make sure it's in directory /usr/src/
  • If you already have a directory there called linux move it to another name which more properly describes it, with a command such as mv linux linux-2.2.14
  • If, on the other hand, you already have a linux which is currently pointing to some other directory, break the link with rm linux
  • After you've un-zipped and un-tarred the kernel, make sure it's in a sub-directory of /usr/src/. Its name should fully describe it, such as /usr/src/linux-2.4.0
  • Create a symbolic (soft) link to it named (just) linux with something like ln -s /usr/src/linux-2.4.0 linux

Three kernel configuration tools

What do you want your kernel to look like? There are a lot of questions to be answered.

  1. make config is the (painful) question after question after question console dialogue version
  2. make menuconfig is the slightly less painful console version
  3. make xconfig is the X version and is easiest to use

Miscellaneous considersiderations

  • If you want frame buffer support, you'll need to request "Code Maturity Level" that includes prompts for development and/or incompletes.
  • Since I wanted frame buffer support, I asked for these experimental modules (which reflect my hardware)
    • nVidia Riva Support
    • ATI Mach64 display support
    • ATI Rage128 display support
  • In "Character devices" I also chose to enable "Support for console on serial terminal". If, as a result of what you've done, Linux thinks there's no VGA console here, startup console messages will go to this serial port.
    Under normal circumstances, ie: when VGA does exist, this by itself does not redirect console messages to the serial port. You must also pass a kernel command line option at the LILO prompt with something like
          console=/dev/ttyS0
    or add this option to an append line in lilo.conf

The process

Go through each and every selection in the menus given. If you are not sure what an option is used for, click on the HELP button for more information. If you're still not sure, look for a Documentation sub-directory in the tree. That directory consists of files and other sub-directories. Each directory contains a file called 00-INDEX which tells you more of what's there. This will be a time consuming process. Make sure you document what you did in case you have to re-visit it later!

When you have selected all of the options you would like in your "custom" kernel configuration, you will have finished the hard part.

  1. Select Store Configuration to File in order to save a copy of your configuration selections. You can use this file later if you need to do this again.
  2. This is particularly handy if you have several different config versions. The very last configuration you used is also stored in a file named .config
  3. Select Save and Exit
Now...
  • make dep checks dependencies and updates .depend
  • make clean
  • make bzImage which will create a compressed kernel image file called /usr/src/linux/arch/i386/boot/bzImage (Don't get sucked in as I did by /usr/src/linux/vmlinux which is the uncompressed kernel image.)
(The "b" in bzImage means this will be a big Image.)
(The "z" in bzImage means this will be a compressed Image.)

An alternative to make bzImage which I don't like is make bzlilo For my liking, it goes too far. Not only does it make a kernel image file, it also
   puts that image into /boot
   adjusts /etc/lilo.conf (in ways I don't like)
   and even runs /sbin/lilo

That's a little too much for me! I'd prefer to do those steps myself. Call me paranoid, but I prefer to be a little more hands-on and to run lilo in test mode /sbin/lilo -t first!

The next steps concern modules and are only needed if you are going to be using a modular kernel, which is the preferred way. (The alternative is a monolithic kernel.)

  • make modules
  • make modules_install
(These two steps took me about 10-15 minutes to complete.)
Copy the new image into your /boot partition, giving it a meaningful name, with something like this:

cp /usr/src/linux/arch/i386/boot/bzImage /boot/vmlinuz-2.4.10

OK! Now your new kernel has been built and has been placed in /boot Now you have tell LILO about it. (There's a reasonably full discussion on LILO here in another section of these notes.)

  • Make sure you add a new stanza into your /etc/lilo.conf leaving the other ones in tact. In case the new kernel screws up, you'll want the option of being able to boot an old one!
  • The new stanza ought to be configured quite similarly to the old one there with the exception of the image= which will point to your new kernel and the label= which will be whatever text label you want to associate with this new kernel.
  • Run /sbin/lilo -t   If it's looking good,
  • Run /sbin/lilo and reboot your system
Once you've rebooted, the command uname -r can be used to report on which kernel is running and when it was built.