View source for Kernel configuration

[[Category:Documentation]]
Configuring your kernel is something that is often overlooked by new LFScript users. However, it is very important that you create a configuration file. It often makes the difference between a usable system and one that only gives you a kernel panic.

== Downloading the kernel source ==

LFScript is capable of downloading all source code you need, automatically. The Linux kernel is part of the basic LFS system, which means that the next command will also download the kernel source for you:

<pre>./lfscript -BS</pre>

All source code is saved to the <code>sources</code> directory.

<pre>cd sources</pre>

== Configuring the kernel ==

Extract your kernel source, and enter the source directory:

<pre>tar xf linux-3.*.tar.bz2
cd linux-3.*</pre>

It is recommended that you clean the source tree first:

<pre>make mrproper</pre>

Next, create a default configuration. This gives you a basis to build your own configuration on. You can create kernel configurations for other CPU's than you are currently using by supplying the '''ARCH=<TYPE>''' option:

<pre>make ARCH=x86_64 defconfig</pre>

or

<pre>make ARCH=i386 defconfig</pre>

If you already have a configuration file from an earlier build, you can upgrade it in stead of starting from scratch. Replace '''x86_64''' in the next command with your target architecture:

<pre>cp -v <LOCATION OF OLD CONFIG> .config
make ARCH=x86_64 oldconfig</pre>

The kernel source comes with a configuration tool included called <code>menuconfig</code>. Menuconfig has an ncurses based text user interface, which allows easy selection of the features you like to include in your kernel.

If your host system does not have the ncurses development package installed, the command may fail. On Ubuntu, for example you may need to run the next command, prior to <code>make menuconfig</code>:

<pre>sudo apt-get install ncurses-dev</pre>

Then, start the configuration tool. Replace '''x86_64''' in the next command with your target architecture:

<pre>make ARCH=x86_64 menuconfig</pre>

You can navigate the menu using the up and down keys, pressing enter to enter a submenu.

To select an option to include in the kernel, press <code>Y</code>. The option should become prefixed with a checked box: <code>[*]</code>.

=== Important things to include ===

Recent development versions of LFS require you to include support for <code>devtmpfs</code>:

<pre>Device Drivers --->
  Generic Driver Options --->
     Maintain a devtmpfs filesystem to mount at /dev</pre>

You should also be sure to include support for the file systems you want to use when you install your system:

<pre>File systems --->
  Second extended fs support
  Ext3 journalling file system support
  The Extended 4 (ext4) filesystem</pre>

If you want to build a Live CD of your system, you also need SquashFS support:

<pre>File systems --->
  Miscellaneous filesystems --->
    SquashFS 4.0 - Squashed file system support --->
      Include support for ZLIB compressed file systems
      Include support for LZO compressed file systems
      Include support for XZ compressed file systems</pre>

=== fsOS Live CD ===

In the <code>fsos</code> folder in LFScript, there is a text file called <code>kernel.features</code>. It contains a complete list of everything selected for the [[fsOS]] Live CD.

== Saving your configuration ==

When you quit the configuration tool, it will ask you if you want to save your configuration; Choose "yes".

Next, move the configuration file out of the kernel source:

<pre>cp -v .config ../../my_kernel.config</pre>

You don't need the kernel source tree any more, so remove it:

<pre>cd ../../
rm&nbsp;-rf sources/linux-3.*/</pre>

== Using your configuration with LFScript ==

You can present your configuration to LFScript with the [[LFScript Switches|-k switch]]:

<pre>./lfscript <options> -k my_kernel.config</pre>

The following command will rebuild your kernel, this may be useful if you have changed your configuration file:

<pre>./lfscript -BU kernel -k my_kernel.config</pre>