Operating System Kernel Compilation

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 • 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 4.15.4 (bleeding edge stable version)

14. Kernel Repository • http://kernel.org – 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-4.15.4.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-4.15.4 $> make defconfig

22. Compiling the Kernel • Issue ‘make’ inside the source directory $> make • 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-4.15.4 4.15.4

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