The Linux Kernel HOWTO: Quick Steps

2. Quick Steps - Kernel Compile

This section is written by Al Dev (alavoor@yahoo.com)

The latest version of this section is at http://www.aldev.8m.com and click on "Quick Steps to recompile linux kernel". Mirror sites are at - http://aldev.webjump.com, angelfire, geocities, virtualave, bizland, theglobe, spree, infoseek, bcity, 50megs, NBCi, Terrashare, Fortunecity, Freewebsites, Tripod. These sites have lots of linux goodies and tips.

A copy of the above web-site is reproduced here -

Kernel re-compile is required in order to make the kernel very lean and which will result in FASTER operating system . It is also required to support any new devices. Note: Below 'bash#' denotes the bash prompt, you should type the commands that appear after the 'bash#' prompt. Below are commands tested on Redhat Linux, but it should work for other distributions with very minor changes.

Note: You can have many kernel images on your system. By following the steps below you do not overwrite or damage your existing kernel. These steps are very safe and your current kernel will be intact and will not be touched.
Login in as 'root' throughout all these steps. Mount Redhat linux cdrom and install the linux kernel source rpm
```
bash$ su - root
bash# cd /mnt/cdrom/RedHat/RPMS 
bash# rpm -i    kernel-headers*.rpm 
bash# rpm -i    kernel-source*.rpm 
bash# rpm -i dev86*.rpm   
bash# rpm -i bin86*.rpm   
```
(The bin86*.rpm and 'as86' is required only for OLDER Linux systems like redhat 5.x. Get Intel assembler 'as86' command from dev86*.rpm on cdrom or from http://rpmfind.net/linux/RPM/mandrake/7.1/Mandrake/RPMS/bin86-0.4-12mdk.i586.html , http://rpmfind.net/linux/RPM/kondara/jirai/i586/bin86-0.4-8k.i586.html ).
Start X-windows with 'startx'.
```
bash# man startx
bash# startx
bash# cd /usr/src/linux 
bash# make xconfig 
```
The "make xconfig" brings up a user friendly GUI interface! DO NOT use 'make config' which is a command-line option ( use this ONLY if you CANNOT bring up X-window). You can load the configuration file from /usr/src/linux/.config (dot config file. Note the dot before config).
Enable the Loadable kernel modules support! With this option you can load/unload the device drivers dynamically on running linux system on the fly. See these man pages
```
bash# man lsmod
bash# man insmod
bash# man rmmod
bash# man depmod
```
Save and Exit "make xconfig". All the options which you selected is now saved into configuration file at /usr/src/linux/.config (dot config file). And now, do -
```
bash# make dep
bash# make clean
```

Read the following file (to gain some knowledge about kernel building. Tip: Use the color editor gvim for better readability.

bash# gvim -R   /usr/src/linux/arch/i386/config.in 
bash# man less 
bash# less   /usr/src/linux/arch/i386/config.in 
Type 'h' for help and to navigate press i, j, k, l, h or arrow, page up/down keys.

Now, give the make command -

        bash# cd /usr/src/linux
        bash# man nohup
        bash# nohup make bzImage &  
        bash# tail -f nohup.out     (.... to monitor the progress) 
This will put the kernel in /usr/src/linux/arch/i386/boot/bzImage 
        bash# man tail

After bzImage is successful, copy the kernel image to /boot directory. You must copy the new kernel image to /boot directory, otherwise the new kernel MAY NOT boot. And then read the manual page on lilo (see also http://www.linuxdoc.org/HOWTO/LILO-crash-rescue-HOWTO.html) and see the sample lilo.conf file. Always give a date extension to the filename, because it tells you when you built the kernel, as shown below:
```
bash# cp /usr/src/linux/arch/i386/boot/bzImage     /boot/bzImage.myker.26mar2001
bash# man lilo
bash# man lilo.conf
And edit /etc/lilo.conf file and put these lines - 
        image=/boot/bzImage.myker.26mar2001 
        label=myker
        root=/dev/hda1 
        read-only 
You can check device name for 'root=' with the command - 
        bash# df   /boot 
```
Now give
```
bash# lilo 
bash# lilo -q 
```
You must re-run lilo even if entry 'myker' exists, everytime you create a new bzImage.
Reboot the machine and at lilo press tab key and type 'myker' If it boots then you did a good job! Otherwise at lilo select your old kernel, boot and re-try all over again. Your old kernel is still INTACT and SAFE at say /boot/vmlinuz-2.0.34-0.6
Loadable Modules: Check for insmod command which is extensively used for loading the modules.
```
bash# man insmod
bash# insmod 
bash# rpm -i /mnt/cdrom/Redhat/RPMS/modutils*.rpm
```
The step given below may not be required but is needed ONLY FOR EMERGENCIES where your /lib/modules files are damaged. If you already have the /lib/modules directory and in case you want replace them use the --force to replace the package and select appropriate cpu architecture. For new versions of linux redhat linux 6.0 and later, the kernel modules are included with kernel-2.2*.rpm. Install the loadable modules and the kernel with
```
        This will list the already installed package.
bash# rpm -qa | grep -i kernel
        
bash# rpm -U --force  /mnt/cdrom/Redhat/RPMS/kernel-2.2.14-5.0.i686.rpm
(or)
bash# rpm -U --force  /mnt/cdrom/Redhat/RPMS/kernel-2.2.14-5.0.i586.rpm
(or)
bash# rpm -U --force  /mnt/cdrom/Redhat/RPMS/kernel-2.2.14-5.0.i386.rpm
```
This is only for old versions of redhat linux 5.2 and before. Boot new kernel and install the loadable modules from RedHat Linux "contrib" cdrom
```
bash# rpm -i /mnt/cdrom/contrib/kernel-modules*.rpm 
....(For old linux systems which do not have insmod pre-installed) 
```
This step is required ONLY if you had downloaded a new version of linux kernel source. Loadable module are located in /lib/modules.
```
bash# cd /usr/src/linux
bash# make modules
bash# make modules_install
```
If your new kernel 'myker' boots and works properly, you can create the boot disk. Insert a blank floppy into floppy drive and -
```
bash# cd /usr/src/linux
bash# make bzdisk
See also mkbootdisk -
bash# rpm -i mkbootdisk*.rpm
bash# man mkbootdisk
```

2.1 Troublshoot Common Mistakes

The following mistake is commited very frequently by new users.

If your new kernel does not boot and you get -

Warning: unable to open an initial console
Kernel panic: no init found. Try passing init= option to kernel

The problem is that you did not set the "root=" parameter properly in the /etc/lilo.conf. In my case, I used root=/dev/hda1 which is having the root partition "/". You must properly point the root device in your lilo.conf, it can be like /dev/hdb2 or /dev/hda7.

The kernel looks for the init command which is located in /sbin/init. And /sbin directory lives on the root partition. For details see -

bash# man init

2.2 Sample lilo.conf

Given below is a sample /etc/lilo.conf file. You should follow the naming conventions like ker2217 (for kernel 2.2.17), ker2214 (for kernel 2.2.14). You can have many kernel images on the same /boot system. On my machine I have something like:

boot=/dev/hda
map=/boot/map
install=/boot/boot.b
prompt
timeout=50
default=firewall

image=/boot/vmlinuz-2.2.14-5.0
        label=ker2214
        read-only
        root=/dev/hda9

image=/boot/vmlinuz-2.2.17-14
        label=ker2217
        read-only
        root=/dev/hda9

#image=/usr/src/linux/arch/i386/boot/bzImage 
#       label=myker 
#       root=/dev/hda7
#       read-only 

image=/boot/bzImage.myker.11feb2001
        label=myker11feb 
        root=/dev/hda9
        read-only 

image=/boot/bzImage.myker.01jan2001
        label=myker01jan 
        root=/dev/hda9
        read-only 

image=/boot/bzImage.myker-firewall.16mar2001
        label=firewall 
        root=/dev/hda9
        read-only

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