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://aldev0.webjump.com, angelfire, geocities, virtualave, 50megs, theglobe, NBCi, Terrashare, Fortunecity, Freewebsites, Tripod, Spree, Escalix, Httpcity, Freeservers.

These sites have lots of linux goodies and tips.

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 bin86-mandrake , bin86-kondara ).
- Start X-windows with 'startx'. If you are not able to start X-window then see next step below.
```
        bash# man startx
        bash# startx
        bash# cd /usr/src/linux 
        bash# make xconfig 
```
- If you are not able to start X-window above then try -
```
        bash# make menuconfig
If the above command fails then try -
        bash# make config
```
The "make xconfig" or "make menuconfig" brings up a user friendly GUI interface. You can load the configuration file from /usr/src/linux/.config (dot config file. Note the dot before config).
Within 'make xconfig' you must do these to avoid problems -
- Select proper CPU type - Pentium 3, AMD K6, Cyrix, Pentium 4, Intel 386, DEC Alpha, PowerPC otherwise kernel will not boot!!
- Select SMP support - whether single CPU or multiple CPUs
- Filesystems - Select Windows95 Vfat, MSDOS, NTFS as part of kernel and not as loadable modules.
- 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# rpm -i /mnt/cdrom/Redhat/RPMS/modutils*.rpm
bash# man lsmod
bash# man insmod
bash# man rmmod
bash# man depmod
bash# man modprobe
```
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   / 
```
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
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
```
LOADABLE MODULES: This step is required ONLY if you had enabled Loadable module support in step 3 above. Loadable module are located in /lib/modules. You MUST do this step if you enabled or disabled any modules, otherwise you will get 'unresolved symbols' errors during or after kernel boot. Check for insmod command which is extensively used for loading the modules.
```
bash# cd /usr/src/linux
bash# make modules
bash# make modules_install
bash# man insmod
bash# insmod 
```
This will copy the modules to /lib/modules directory.

2.1 Troublshoot Common Mistakes

No init found

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

Kernel does not load module - Unresolved symbol error messages

When you boot kernel and system tries to load any modules and you get "Unresolved symbol : __some_function_name" then it means that you did not clean compile the modules and kernel. It is mandatory that you should do make clean and make the modules. Do this -

        bash# cd /usr/src/linux
        bash# make dep
        bash# make clean
        bash# nohup make bzImage &  
        bash# tail -f nohup.out     (.... to monitor the progress) 
        bash# make modules
        bash# make modules_install

Kernel fails to load a module

If the kernel fails to load a module (say loadable module for network card or other devices), then you may want to try to build the driver for device right into the kernel. Sometimes loadable module will NOT work and the driver needs to be built right inside the kernel. For example - some network cards do not support loadable module feature - you MUST build the driver of the network card right into linux kernel. Hence, in 'make xconfig' you MUST not select loadable module for this device.

Loadable modules

You can install default loadable modules with -

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)

2.2 Post Kernel Building

After successfully building and booting the Linux kernel, you may be required to do these additional steps to make some of the devices to work with Linux. (The steps below were tested on Redhat Linux but should work with other distributions as well.)

Video card/Monitor configuration:

Please see the video card manual which is usually shipped with the PC. You should look for a "Technical Specifications" page.
Please see the monitor's manual and look for a "Technical Specifications" page.

You can configure the Video card and monitor by using these commands:

bash$ su - root
bash# man Xconfigurator
bash# /usr/bin/X11/Xconfigurator --help
bash# /usr/bin/X11/Xconfigurator 
bash# /usr/bin/X11/Xconfigurator --expert

If your card is not detected automatically, then you can use the --expert option and select the "Unlisted card". If your monitor is not listed then select the generic monitor type SVGA 1024x768.

Sound card configuration:

Connect your external speakers to the sound card's audio port.
Connect your CDROM audio wire to sound card's audio 4-pin socket. (Otherwise your cdrom drive will not play the music from your music cd)
Refer to HOWTO docs on 'Sound' at http://www.linuxdoc.org

bash$ su - root
bash# man sndconfig
bash# /usr/sbin/sndconfig

Then start X-window 'KDE desktop' with 'startx' command. Click on 'K Start->ControlCenter->SoundServer->General->Test Sound'. This should play the test sound. Then click on 'K Start->MultiMedia->SoundMixer->SoundVolumeSlider' and adjust the sound volume.

Network card configuration:

Use /sbin/linuxconf
Or use KDE control panel
Refer to HOWTO docs on 'Networking' at http://www.linuxdoc.org

Configure Firewall and IP Masquerading : For Linux kernel version 2.4 and above, the firewall and IP Masquerading is implemented by NetFilter package. Hence in kernel config you should enable Netfilter and run the Firewall/IPMasq script. Download the scripts from Firewall-IPMasq scripts , main page of Netfilter is at http://netfilter.samba.org. Related materials at firewalling-matures and Netfilter-FAQ.

For kernel version below 2.4 you should install the firewall rpms from rpmfind.net or firewall.src.rpm.

Configuration of other devices: Refer to HOWTO docs relating to your devices at http://www.linuxdoc.org

2.3 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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