How to: Compile Linux kernel 2.6

Posted on in Categories CentOS, Debian Linux, GNU/Open source, Howto, Linux last updated May 5, 2012

Compiling custom kernel has its own advantages and disadvantages. However, new Linux user / admin find it difficult to compile Linux kernel. Compiling kernel needs to understand few things and then just type couple of commands. This step by step howto covers compiling Linux kernel version 2.6.xx under Debian GNU Linux. However, instructions remains the same for any other distribution except for apt-get command.

Step # 1 Get Latest Linux kernel code

Visit http://kernel.org/ and download the latest source code. File name would be linux-x.y.z.tar.bz2, where x.y.z is actual version number. For example file inux-2.6.25.tar.bz2 represents 2.6.25 kernel version. Use wget command to download kernel source code:
$ cd /tmp
$ wget http://www.kernel.org/pub/linux/kernel/v2.6/linux-x.y.z.tar.bz2

Note: Replace x.y.z with actual version number.

Step # 2 Extract tar (.tar.bz3) file

Type the following command:
# tar -xjvf linux-2.6.25.tar.bz2 -C /usr/src
# cd /usr/src

Step # 3 Configure kernel

Before you configure kernel make sure you have development tools (gcc compilers and related tools) are installed on your system. If gcc compiler and tools are not installed then use apt-get command under Debian Linux to install development tools.
# apt-get install gcc

Now you can start kernel configuration by typing any one of the command:

  • $ make menuconfig – Text based color menus, radiolists & dialogs. This option also useful on remote server if you wanna compile kernel remotely.
  • $ make xconfig – X windows (Qt) based configuration tool, works best under KDE desktop
  • $ make gconfig – X windows (Gtk) based configuration tool, works best under Gnome Dekstop.

For example make menuconfig command launches following screen:
$ make menuconfig

You have to select different options as per your need. Each configuration option has HELP button associated with it so select help button to get help.

Step # 4 Compile kernel

Start compiling to create a compressed kernel image, enter:
$ make
Start compiling to kernel modules:
$ make modules

Install kernel modules (become a root user, use su command):
$ su -
# make modules_install

Step # 5 Install kernel

So far we have compiled kernel and installed kernel modules. It is time to install kernel itself.
# make install

It will install three files into /boot directory as well as modification to your kernel grub configuration file:

  • System.map-2.6.25
  • config-2.6.25
  • vmlinuz-2.6.25

Step # 6: Create an initrd image

Type the following command at a shell prompt:
# cd /boot
# mkinitrd -o initrd.img-2.6.25 2.6.25

initrd images contains device driver which needed to load rest of the operating system later on. Not all computer requires initrd, but it is safe to create one.

Step # 7 Modify Grub configuration file – /boot/grub/menu.lst

Open file using vi:
# vi /boot/grub/menu.lst

title           Debian GNU/Linux, kernel 2.6.25 Default
root            (hd0,0)
kernel          /boot/vmlinuz root=/dev/hdb1 ro
initrd          /boot/initrd.img-2.6.25
savedefault
boot

Remember to setup correct root=/dev/hdXX device. Save and close the file. If you think editing and writing all lines by hand is too much for you, try out update-grub command to update the lines for each kernel in /boot/grub/menu.lst file. Just type the command:
# update-grub
Neat. Huh?

Step # 8 : Reboot computer and boot into your new kernel

Just issue reboot command:
# reboot
For more information see:

  • Our Exploring Linux kernel article and Compiling Linux Kernel module only.
  • Official README file has more information on kernel and software requirement to compile it. This file is kernel source directory tree.
  • Documentation/ directory has interesting kernel documentation for you in kernel source tree.

How to save your live CD session online

Posted on in Categories News last updated September 27, 2005

I use different Live distro for various purpose. Either you can save data on USB pen or hard disk partition. Most of the time all modification or downloads during a Live CD session is kept in RAM until system is rebooted… and then it’s gone/lost.
However new live CD called SLAX allow you to save your session online :D This is very handy as I use multiple computers. Visit online to download CD and read more on webconfig online.

FreeBSD Enable Security Port Auditing to Avoid Vulnerabilities With portaudit

Posted on in Categories FreeBSD, Howto, Security, Sys admin, Tip of the day, Tips last updated February 27, 2008

This is new nifty and long term demanded feature in FreeBSD. A port called portaudit provides a system to check if installed ports are listed in a database of published security vulnerabilities. After installation it will update this security database automatically and include its reports in the output of the daily security run. If you get message like as follows

Vulnerability check disabled, database not found

You need install small port called portaudit. From the man page:

portaudit checks installed packages for known vulnerabilities and generates reports including references to security advisories. Its intended audience is system administrators and individual users. portaudit checks installed packages for known vulnerabilities and generates reports including references to security advisories. Its intended audience is system administrators and individual users.

Install portaudit

1) Install port auditing (login as root)
# cd /usr/ports/ports-mgmt/portaudit
Please note that old portaudit port was located at /usr/ports/security/portaudit/.
2) Install portaudit:
# make install clean
Output:

===>  WARNING: Vulnerability database out of date, checking anyway
===>  Extracting for portaudit-0.5.12
===>  Patching for portaudit-0.5.12
===>  Configuring for portaudit-0.5.12
===>  Building for portaudit-0.5.12
===>  Installing for portaudit-0.5.12
===>   Generating temporary packing list
===>  Checking if ports-mgmt/portaudit already installed
===>   Compressing manual pages for portaudit-0.5.12
===>   Registering installation for portaudit-0.5.12
===>  Cleaning for portaudit-0.5.12

3) Fetch the database so that port auditing get activated immediately. By default it install a shell script ‘portaudit’ in /usr/local/etc/periodic/security/:
# /usr/local/sbin/portaudit -Fda
Output:

auditfile.tbz                                 100% of   47 kB  405 kBps
New database installed.
Database created: Wed Feb 27 06:10:01 CST 2008
0 problem(s) in your installed packages found.

Where,

  • -F: Fetch the current database from the FreeBSD servers.
  • -d: Print the creation date of the database.
  • -a: Print a vulnerability report for all installed packages

4) portaudit script automatically get called via FreeBSD’s periodic (cron job) facility. So your database get updated automatically everyday.

Let us assume you would like to install a port called sudo. If it has known vulnerabilities it will not install sudo:
# cd /usr/ports/security/sudo
# make install clean

===>  sudo-1.6.8.7 has known vulnerabilities:
=> sudo -- local race condition vulnerability.
   Reference: &tt;http://www.FreeBSD.org/ports/portaudit/3bf157fa-
e1c6-11d9-b875-0001020eed82.html>
=> Please update your ports tree and try again.
*** Error code 1

Stop in /usr/ports/security/sudo.

For more information refer portaudit man page:
$ man portaudit