1. Operating System Kernel Compilation
Sarah Diesburg
CS 3430
Operating Systems

2. Kernel Coding The next project involves compiling a new kernel!
Fun but challenging….
Each person/team will get their own virtual machine(s)
See website instructions for how to install/use the virtual machine

3. Booting with the Bootloader (grub2)
The newest version of the kernel will boot by default
Look in the submenu (or further down the list) for any older version

4. Logging In
Username: os
Password: os
Username: root
Password: iamr00t

5. No GUI/Desktop? I disabled it by default (to run faster)
If you really want it, issue (as root)
#> systemctl set-default multi-user.target
If you want to turn it off again, issue (as root)
#> systemctl set-default graphical.target

6. Communicating with your fresh virtual machine
Use ssh
Log into the terminal, and issue /sbin/ifconfig to get the second IP address
Type the IP address directly into PuTTY
Transfer files
Must use Winscp or Filezilla with the IP address found above
Basically, communicate with it the same way you communicated with the student.cs.uni.edu machine

7. SSH/WinSCP Demo…

8. If you created your own virtual machine….
Good for you!
You will want to install these packages:
gcc
make
ssh
vim / emacs / (your choice of editor)
sudo
libncurses5-dev
others (heh heh)

9. Basic System Commands $> passwd $> su $> sudo
Change your password
$> su
Become root directly. Use root’s password when prompted.
$> sudo
Do something with root’s privileges without having to become root

10. Basic System Commands $> chown –R os:os <dir>
Changes ownership of dir to user/group os
$> adduser <username>
Adds user specified by username
$> userdel <username>
Deletes user specified by username

11. Kernel Compilation

12. Example of Kernel Compilation….

13. Choosing a Kernel The next project will involve kernel development
We all need to be in the same boat…
The class version will be (bleeding edge stable version)

14. Kernel Repository
– place to download latest and greatest Linux kernels!
Traditional place for kernel is in /usr/src/
It is already in there for you
…That is, unless you created your own virtual machine. Then download it from kernel.org, and extract it with the command
$> tar xv linux tar.xz

15. Compiling the Kernel
Compiles based on configuration of .config file located in the kernel source directory
How can I correctly configure my kernel?
Use the ‘make defconfig’ command
Use the ‘make menuconfig’ command

16. ‘make defconfig’
This new command makes the default configuration file for Linux.
It creates a smaller configuration file than previous methods, so the kernel is faster to compile

17. ‘make menuconfig’
Only do this if you are trying to make the kernel smaller
Manually select and deselect drivers and options for your kernel
* -- compiled directly into kernel
M – compiled into a module (driver) that can be dynamically added
Can be tough to figure out what you need and don’t need
Command ‘lspci’ shows hardware on computer

18. ‘make menuconfig’

19. ‘lspci’

20. General Linux Source Organization
Memory Management
Networking Layer
Security
Sound Processing
Architecture-specific Code
Disk Drivers
Devices
File Systems

21. Config Example (Inside Source Dir)
$> cd /usr/src/linux $> make defconfig

22. Compiling the Kernel Issue ‘make’ inside the source directory
Grab some coffee….

23. Installing the Kernel Install the modules (drivers)
$> sudo make modules_install
Install the actual kernel
$> sudo make install
What does ‘sudo’ do?

24. Historical final steps
Now the ‘make install’ command does all the following for you
Create a ramfs image
Update grub

25. Boot Driver Problem Why ramfs?
Suppose you compiled the disk drivers and root file system drivers as modules
Boot process loads the kernel image
Kernel image does not contain disk drivers

26. Boot Driver Solutions
Hard: Figure out all drivers needed to read the root file system and compile into kernel
May take a few tries…
Easy: Create a root file system image file that will load the right modules for you
initramfs
(Remember, ‘make install’ does this for you already, so you do not have to do the following steps anymore…)

27. initramfs Create the initramfs image $> cd /boot
$> sudo mkinitramfs –o /boot/initrd.img

28. Configure the Boot Loader (Grub)
Update bootloader (no longer necessary with ‘make install’)
$> sudo update-grub
Now you can issue a reboot and cross your fingers!
$> sudo reboot

29. Telling Which Kernel You are In
Select the new kernel from the grub menu!
Watch your virtual machine
If something goes wrong, reboot and go back into your original kernel to try again
The following command will tell you which kernel you are in:
$> uname -r

30. Uh oh…. If it doesn’t boot, go back into the original kernel
Always important to have one working kernel!
Make sure you didn’t skip a step…
You may have taken too much out of the kernel…
Start with bloated kernel, take things out one by one

31. Next Time… More on Project 2
Loading a kernel module and playing with proc files