Linux Kernel 1: How to Compile Linux Kernel

I. Introduction:

This post is the first post for linux kernel hacking. Before you can dig into linux kernel source you should first learn how to build a kernel yourself.

There are many distributions out there, and I prefer to use Slackware 14, gentoo or debian (not dibian based distro such as ubuntu, mint). The reason I recommend to use these two distro is because that most modern distributions have changed so many linux codes that may confused you while your are tracing linux code.

II. Environment:

• Linux Distro: Slackware 14 x86_64
• kernel version: 3.2.37
• gcc version: 4.7.1

III. Contents:

1. pre-requirement:

The first thing you should do is download the kernel source that you want to build. The kernel source file can be found in : http://www.kernel.org/pub/linux/kernel/.

In my case, "linux-3.2.37.tar.bz2". Just extract the file and put it into the directory that you want. I put the source code in "$HOME/kernel/".

2. config:

Before building the kernel, you have to config it first.  type "make help" and you can see a list of options. In this part, we just focus on the config sections.

The following  are some options that are commonly used.

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config          - Update current config utilising a line-oriented program
menuconfig      - Update current config utilising a menu based program
xconfig         - Update current config utilising a QT based front-end
gconfig         - Update current config utilising a GTK based front-end
oldconfig       - Update current config utilising a provided .config as base
localmodconfig  - Update current config disabling modules not loaded
localyesconfig  - Update current config converting local mods to core

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The description is very self-explained therefore I'm not going to explain it. Just a quick note, if you prefer the GUI interface, type "make xconfig/gconfig" which will give you gui interface to config the kernel. In my case I use "make localmodconfig" which will set the config file according to your system modules.

------------------------------------[update]---------------------------------------------------------
 you can also use "gcat /proc/config.gz > .config" if your previous kernel has enable the IKCONFIG  and IKCONFIG_PROC flag. This will copy the previous kernel configuration to your current kernel source. After you finished the above command you can still type "make oldconfig" if you are using a newer kernel. (The newer kernel may have some new features )
Thank you +Eric Garland. :)

3. build the kernel:

If this is the first time you compile this kernel Type "make all -j8" to compile the kernel. The "make help" output tell us that the make install will build the target marked * and the default one is "vmlinuz" and "modules".

However, if u have compiled the kernel before and there is no new featured that is added in the config file.You can type "make vmlinuz -j8" instead. It will only build the vmlinuz and will not build the modules.

If you have add a new modules or edit the modules source code you can type "make modules -j8" to only compile the linux modules.

P.S Compiling the linux kernel may take some time according to your hardware. (get a cup of coffee or watch a movie :P)

4. Install the modules:

If this is the first time you build the linux kernel: type "sudo make modules_install". If your haven't modify any kernel modules or add a new one in the config file, this step can be skiped.

5. Install the kernel:

Instead of typing "make install" I prefer using the following command.

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sudo cp arch/x86_64/boot/bzimage /boot/vmlinuz-3.2.37

sudo mkinitrd -c -k 3.2.37 -m ext4 -f ext4 -r /dev/sdaN -o /boot/initrd-3.2.37.img

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More detailed about mkinitrd command, type "man mkinitrd" or check out this link: http://mirrors.slackware.com/slackware/slackware-11.0/extra/linux-2.6.17.13/README.initrd

6. Update your bootloader:

Since I'm using slackware and the default bootloader of slackware is lilo, so I have to edit the /etc/lilo.conf. After modified the /etc/lilo.conf type "sudo lilo".

7. Command Walk through:

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        // if this is the first time you compile the kernel

make mrproper;

// if this is the first time you compile the kernel or want to add some new features to your kernel.

make localmodconfig/menuconfig/xconfig/gconfig;

make all && make modules_install; // if this is the first time you compile the kernel or adding new stuff to the

make vmlinuz; // if you just change the kernel source

make modules && make modules_install; // if you have add a new module in config file or modify the module source code

cp arch/x86_64/boot/bzimage /boot/vmlinux-3.2.37

mkinitrd -c -k 3.2.37 -m ext4 -f ext4 -r /dev/sda2

-----update your bootloader----

echo "done";

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IV Conclusion:

This is basically how to compile a linux kernel. I will talk about some more configuration and some tools to help you trace the linux code. Happy Hacking.