CS3013 Project O

Due date: (Not due)

Note, you must have formed groups and received your machine and root password from the TAs before starting this project.

Index

• Overview
• Specifics
  • Administrative
  • Tools
  • Re-Compiling the Kernel
  • Fossil Lab Use
• Questions
• Hotlinks

Overview

The last project for this course will involve modifying the Linux kernel. This project is designed to get you familiar with the Linux system: how to create and add users, how to use some common Unix tools, where the kernel (the operating system) source code is located, how to re-compile the kernel and reboot, and how to save your work onto the Fossil server. The set of commands is not intended to be exhaustive. Rather, it is to get you started on the kinds of things you will need to do for future projects.

As you work the project below, feel free to explore further than the basic commands below, if you so desire. Refer to the Hotlinks section for more information on Linux and the Fossil lab. You may also send questions to the TA mailing list at cs3013_ta@cs.wpi.edu.

Have fun!

Specifics

Administrative

You will be the system administrator for your Linux machine for the entire term. Fortunately, this will not typically involve much effort, as each machine is configured to provide the necessary initial configuration to do all projects. Here, you will create some user accounts and give them the ability to access system-private stuff as root.

Carry out following steps:

1. Log into your machine as user root. You should then change the root password on the first login. Choose a smart password. Remember, if the machine is compromised, it will hurt you the most!
2. Create a new user account with the command useradd. You may want to use the -m flag, too.
3. Create a password for the new account using the passwd command.
4. Give sudo permissions to the new account by editing the file /etc/sudoers with your favorite editor (emacs, vi or pico, say). If you like vi, you might consider running the command visudo. Add a line to the end of the sudoers file that looks like:

      newuser ALL=(ALL) ALL
   

   replacing "newuser" with your new account name.
5. Add the new account to the group "root" (in /etc/group). You'll need this to get access to linux kernel sources.
6. Change permissions to prevent 'guests' from seeing the Linux source code with the command chmod -R o-rwx /usr/src/linux*
7. Login to the new account to be sure it works. From the same machine use login or su. From a different Fossil machine use slogin or ssh. From a different WPI machine, you must first login to the Fossil server (fossil.wpi.edu) using slogin or ssh.
8. As a user, you may use passwd to change your password or chsh to change your shell as desired.
9. Repeat the above steps for each person in your group.
10. Note, to delete an account use the command userdel, with a -r option to remove home directories. Please note that the user accounts "guest" and "admin" should never be deleted. If you ever find a machine with the "guest" account not working, please report it to the TA mailing list (cs3013_ta@cs.wpi.edu).

After the above steps, you will typically log into your machine as a normal user and then use the sudo command to perform any commands that require root access. This is the preferred method used below.

Tools

Here, you will find where the Linux source code is located, how many lines of code it is, how large the "core" part of the kernel is and locate some specific kernel modules.

1. Go to the main directory of the Linux source code by doing a cd /usr/src/linux.
2. Run the command find to see how many files there are.
3. Run the command find | wc -l to count how many files there are.
4. Run the command find -name '*.c' to see how many .c files there are.
5. Count the lines of source code.
6. Find how many source code files have been copyrighted (at one time, at least) in the kernel (in /usr/src/linux/kernel, the core part of the Linux operating system) by Linus Torvalds using:

   grep -l Linus `find -name '*.c'` | wc -l

Re-Compiling the Kernel

Some of the projects you do for this class will involve re-compiling the kernel and rebooting. You will re-compile the kernel, set it up so that your new kernel will be used instead of the default kernel, and then reboot.

1. Change directory to /usr/src/linux.
2. Type sudo make xconfig. (Enter your user password, if requested by sudo.) Normally, you would customize any aspects of the kernel you need to. In this case, just select "Save and Exit."
3. Type sudo make dep to set up all the dependencies correctly.
4. Type sudo make bzImage to create a compressed kernel image. This will take some time and you can watch the new kernel being built, or go out for a quick cup of coffee and come back. When done, you should have a new kernel in /usr/src/linux/arch/i386/boot/bzImage.
5. In order to boot your new kernel, you'll need to copy the kernel image to the place where a regular bootable kernel is found. Do this with cp /usr/src/linux/arch/i386/boot/bzImage /boot/vmlinuz.proj0.
6. Configure lilo (the Linux boot manager) to enable you to select your new kernel in addition to the old kernel. Edit /etc/lilo.conf (using sudo and your favorite editor) and add the following lines to the end of the file:

     image = /boot/vmlinuz.proj0
       root = /dev/hda5
       label = proj0
   

7. Run lilo to enable it to recognize your new kernel by typing sudo /sbin/lilo.
8. Prepare to reboot. Check if anyone else (your group members, most likely) is logged into your machine using the who command. If there is, ask them to log out (use talk or write or something similar). Once they log out, use sudo /sbin/reboot to reboot the machine. Note, in general, if you cannot reach a remotely logged in user and need to reboot, you may try using sudo /sbin/shutdown -r +5 to reboot it in 5 minutes, sending out warning messages periodically.
9. When the computer reboots, at the "lilo" prompt, type proj0 to select the new kernel you have for booting.

You can use /sbin/reboot to reboot and then select "linux" to get back to the original kernel.

Fossil Lab Use

All the client machines are on a private network. The only remote access to the rest of WPI (and the rest of the Internet) is through the Fossil server (fossil.wpi.edu), which is a Firewall.

Your client machines are not backed up. You should save your source code and any other class-specific files by copying the files to the Fossil server, which is backed up nightly.

1. From your assigned machine, type ssh ccc.wpi.edu and login to a CCC machine (bert, reno ...).
2. From the CCC machine, ping (using ping, of course) your assigned machine.
3. Type slogin fossil.wpi.edu and log into the server (using the account given to you by the TAs).
4. Use slogin to log into your assigned machine.
5. Type scp /usr/src/linux/.config fossil:/home/newuser/config.save to save the linux kernel configuration to the fossil server, replacing "newuser" with your login name. In general, you should use scp to backup your work to the fossil server.

Questions

Hotlinks

The main Fossil home page is at http://fossil.wpi.edu. It has additional information on the Lab itself, system administration, and Linux.

Return to the 3013 Home Page

Send all project questions to the TA mailing list.

Send all Fossil administrative questions to the Fossil mailing list.