Lab 09 - Process Control

• Lab Procedure
• Part 1 - Game the System
• Part 2 - Process Control
• Part 3 - back and fore
• Part 4 - Detach
• Submission
• Rubric

Lab Procedure

Make sure to return to the AWS Learner Lab page (link in Pilot if you forgot to bookmark it) and hit “Start Lab” to turn on your sandbox / AWS instance.

Use ssh to connect to your AWS Ubuntu instance.

Go to the folder that contains your repository (likely named ceg2350-yourgithubusername).

Create a new directory, Lab09.

Create a file named README.md in the Lab09 folder. The Lab 09 Template can be copied from this link:

• https://raw.githubusercontent.com/pattonsgirl/CEG2350/refs/heads/main/docs/Labs/Lab09/LabTemplate.md

You may refer to additional resources outside of the recommended resources provided.

Any resource that you use that contributes to your understanding of exercises in this lab should be cited in the Citations section of your lab answers. To add citations, provide the site and a summary of what it assisted you with. If generative AI was used, include which generative AI system was used and what prompt(s) you fed it.

If you make mistakes with commands in the lab, note them! Writing down what went wrong and what the correction was will significantly help your learning journey. If you cannot find a correction, it will help the TAs or myself understand what point you reached and determine some potential solutions.

Can’t SSH?

If you cannot ssh to your instance anymore, you may have run into one of these scenarios:

• You overwrote the partition table (or partitions) in xvda - this would erase your root / / filesystem.
• You wrote a bad entry in /etc/fstab - if the system cannot mount the disk, the boot process will hang and not complete

If you think one of those scenarios happened to you, you’ll need to go back to AWS Academy Setup and create a new stack. Once you are in the new instance, don’t forget the steps to cloning your GitHub repo:

1. create a new keypair for authentication to GitHub
2. add the public key to your GitHub user settings
3. clone with ssh

Part 1 - Game the system

• Useful commands: apt, which, whereis

Choose a command line game from this site: It’s Foss - Top 10 Command Line Games for Linux

• bastet is what this lab was tested on

In the answer template, document the game name, how you installed it, where the executable is located, and how to run the game.

For the remainder of this lab, you will be running this game to practice controlling processes.

Part 2 - Process control

Create a second ssh session to your AWS instance. You should now have two ssh sessions to your AWS instance. This will be referred to as Shell A and Shell B in the exercises below - you decide which is A and which is B.

• Useful Commands: pstree, ps, kill, pgrep, top / htop

1. Fill out the following table of process related commands:

Action	Command or Keybind
Check process CPU/memory usage
Show running processes
Show detailed process tree
Find a process by name
Kill a process by PID
Force kill a process by PID
Pause / suspend a process by PID
Resume a suspended process by PID

1. Explain the meaning of the following ps fields:

ps field	Meaning
PID
PPID
UID / USER
TTY
STAT
COMMAND / CMD
%CPU
%MEM
PSR

1. Craft a ps command for processes owned by your user that will show the fields: USER / UID, PID, PPID, TTY, STAT, and COMMAND / CMD
2. In Shell A, run the game. Using Shell B, run your ps command. Provide answers to the following, using Shell B to observe the process statuses:
3. For the game:
   • What is it’s process id?
   • What is it’s parent process id?
   • What process is the parent process?
4. Use kill to kill only the game.
   • Describe what the effect was.
5. [Run the game again] Use kill to kill the game and it’s parent process.
   • Describe what the effect was.
6. Create a new ssh session - Shell C - and run the game again. Watch the processes from the other terminal. Describe what happens, using process knowledge in your description, if you close / exit your connection with Shell C and determine if you can reenter the game (resume the process).

Resources

• Linuxize - Ps Command in Linux (List Processes)
• Digital Ocean - How To Use ps, kill, and nice to Manage Processes in Linux

Part 3 - back and fore

• Useful Commands: pstree, ps, kill, bg, job, fg

1. Fill out the following table of job control commands and keybinds:

Action	Command or Keybind
Show current jobs
Run a command in background
Pause current foreground job
Send job to the background
Bring job to the foreground
Kill a background / stopped job

1. Run the game in the foreground.
2. Send a STOP signal to suspend it.
3. Use ps to confirm the process is still alive, but has been stopped. Provide the line of output that relates to the process.
4. Resume the process in the foreground.
5. Send a TERMINATE signal to kill it.
6. Start the game as a background process. Repeat 3 times.
7. Display the output of jobs and your custom output format ps command
   • If jobs is empty, make sure you are running it in the same shell, the controlling terminal, that you created the background jobs.
8. Kill one job.
9. Move one job to the foreground.
10. Describe what happens, using process knowledge in your description, if you close / exit your connection with this shell and determine if you can reenter the game (resume the process).

Resources

• Introduction To Unix Signals Programming - Sending Signals To Processes
• Digital Ocean - How To Use Bash’s Job Control to Manage Foreground and Background Processes

Part 4 - Detach

The perhaps obtuse goal of the previous two exercises is to understand process control, but also to realize that with these methods, your shell connection must remain active. If you end your shell session, the processes attached to it also end. There are tools that allow you to run processes detach from your shell session. This lab will have you use tmux, but other tools exist.

1. Fill out the following table of tmux commands and keybinds:

Action	Command or Keybind
Start a new session and set a name
List tmux sessions
Attach to session by name
Kill session by name
Detach from session
Split pane horizontally
Split pane vertically
Switch panes
Close pane

1. Create a tmux session. Run the game in the session.
2. Leaving your game running, detach from the session.
3. Run your custom formatted ps command, showing processes without a controlling terminal
4. Use tmux to list sessions
5. Close your ssh shell session to your instance, then ssh in again. How can you determine if your tmux session with your game running is available?
6. Reattach to your tmux session running the game.
7. Kill the tmux session

Resources

• RedHat - A beginner’s guide to tmux

Submission

1. Verify that your GitHub repo has a Lab09 folder with at minimum:

   • README.md

2. In the Pilot Dropbox, paste the URL to the Lab09 folder in your GitHub repo

   • URL should look like: https://github.com/WSU-kduncan/ceg2350-YOURGITHUBUSERNAME/tree/main/Lab09

Rubric

Your files should be cleanly presented in your GitHub repository. Citations should be included as needed. Include which generative AI system was used and what prompts were used if generative AI was used.

Rubric