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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, 50megs, theglobe, NBCi, Terrashare, Fortunecity, Freewebsites, Tripod, Spree, Escalix, Httpcity, Freeservers.

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.

  1. 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.

  2. 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 ).

  3. 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). A better alternative to command-line 'make config' is 'make menuconfig' which brings up a user-friendly ncurses text-based menu interface. Some persons like 'make menuconfig' over 'make xconfig'. My personal preference - whenever I cannot bring up the X-window, I use 'make menuconfig'. You can load the configuration file from /usr/src/linux/.config (dot config file. Note the dot before config).

  4. 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# man lsmod
      bash# man insmod
      bash# man rmmod
      bash# man depmod
      bash# man modprobe
      

  5. 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
    

  6. 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. 
    

  7. 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 
    

  8. 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   / 
    

  9. Now give
    bash# lilo 
    bash# lilo -q 
    

    You must re-run lilo even if entry 'myker' exists, everytime you create a new bzImage.

  10. 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

  11. 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) 
    

  12. 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
    

  13. 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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