Process management with supervisor in Raspberry Pi - Cheat Sheet & Quick Revision

Recall & Review

beginner

What is Supervisor in process management?

Supervisor is a tool that helps you start, stop, and monitor processes automatically on your Raspberry Pi. It keeps your programs running and restarts them if they crash.

beginner

How do you install Supervisor on a Raspberry Pi?

You install Supervisor by running sudo apt-get update and then sudo apt-get install supervisor. This sets up the tool to manage your processes.

intermediate

What is a Supervisor configuration file used for?

It tells Supervisor which programs to manage, how to start them, and what to do if they stop. You write the program details in a file usually inside /etc/supervisor/conf.d/.

beginner

How does Supervisor help if a process crashes?

Supervisor automatically restarts the crashed process so your program keeps running without you needing to do anything.

intermediate

What command do you use to reload Supervisor after changing config files?

You run sudo supervisorctl reread to read new configs, then sudo supervisorctl update to apply changes and start or stop processes as needed.

What is the main purpose of Supervisor on a Raspberry Pi?

A To manage and keep processes running automatically

B To update the Raspberry Pi operating system

C To connect to the internet

D To write Python programs

Supervisor manages processes by starting, stopping, and restarting them automatically.

Where do you usually place Supervisor configuration files?

A /var/log/

B /etc/supervisor/conf.d/

C /usr/bin/

D /home/pi/

Supervisor configuration files are placed in /etc/supervisor/conf.d/ to define managed programs.

Which command reloads Supervisor configurations after editing?

A sudo supervisorctl reread

B sudo apt-get update

C sudo reboot

D sudo systemctl start

The command 'sudo supervisorctl reread' tells Supervisor to read new or changed config files.

If a process crashes, what does Supervisor do?

A Sends an email to the user

B Deletes the process files

C Restarts the process automatically

D Shuts down the Raspberry Pi

Supervisor restarts crashed processes to keep them running without manual intervention.

How do you install Supervisor on Raspberry Pi?

A sudo pip install supervisor

B sudo install supervisor

C sudo supervisor install

D sudo apt-get install supervisor

You install Supervisor using the package manager with 'sudo apt-get install supervisor'.

Explain how Supervisor helps manage processes on a Raspberry Pi.

Think about what happens if a program stops unexpectedly.

Describe the steps to add a new program to Supervisor and make it run automatically.

Focus on configuration and commands to apply changes.

Practice

1. What is the main purpose of using supervisor on a Raspberry Pi?

easy

A. To update the Raspberry Pi operating system

B. To install new software packages

C. To manage network connections

D. To automatically restart programs if they stop unexpectedly

Solution

1. Step 1: Understand Supervisor's role

   Supervisor is a tool designed to keep programs running by restarting them if they crash or stop.

2. Step 2: Compare options with Supervisor's function

   Updating the operating system, managing network connections, or installing software packages are tasks Supervisor does not do.

3. Final Answer:

   To automatically restart programs if they stop unexpectedly -> Option D

4. Quick Check:

   Supervisor restarts stopped programs = B [OK]

Hint: Supervisor restarts crashed programs automatically [OK]

Common Mistakes:

• Confusing Supervisor with system update tools
• Thinking Supervisor manages network or installs software
• Assuming Supervisor only monitors without restarting

2. Which of the following is the correct syntax to start Supervisor after installing it on Raspberry Pi?

easy

A. start supervisor

B. supervisor start

C. sudo systemctl start supervisor

D. sudo start supervisor

Solution

1. Step 1: Recall Supervisor service management

   Supervisor runs as a system service managed by systemctl on modern Raspberry Pi OS.

2. Step 2: Identify correct command syntax

   The correct command to start Supervisor service is sudo systemctl start supervisor. Other options are incorrect or incomplete.

3. Final Answer:

   sudo systemctl start supervisor -> Option C

4. Quick Check:

   Use systemctl to start services = A [OK]

Hint: Use 'sudo systemctl start supervisor' to start service [OK]

Common Mistakes:

• Omitting sudo and getting permission errors
• Using incomplete or wrong command like 'supervisor start'
• Confusing with older init.d commands

3. Given this Supervisor config snippet:

[program:myapp]
command=python3 /home/pi/myapp.py
autostart=true
autorestart=true
stderr_logfile=/var/log/myapp.err.log
stdout_logfile=/var/log/myapp.out.log

What happens if myapp.py crashes?

medium

A. Supervisor restarts myapp.py automatically

B. Supervisor stops and does not restart myapp.py

C. Supervisor logs the error but does not restart

D. Supervisor deletes the log files

Solution

1. Step 1: Analyze config options autostart and autorestart

   autostart=true means program starts with Supervisor; autorestart=true means it restarts if it crashes.

2. Step 2: Understand Supervisor behavior on crash

   With autorestart=true, Supervisor will restart myapp.py automatically after a crash.

3. Final Answer:

   Supervisor restarts myapp.py automatically -> Option A

4. Quick Check:

   autorestart=true means auto restart = C [OK]

Hint: autorestart=true means program restarts on crash [OK]

Common Mistakes:

• Thinking logs are deleted on crash
• Assuming Supervisor only logs errors without restart
• Confusing autostart with autorestart

4. You wrote this Supervisor config but your program does not start automatically:

[program:myapp]
command=python3 /home/pi/myapp.py
autostart=false
autorestart=true

What is the problem?

medium

A. autostart is set to false, so program won't start on Supervisor launch

B. command syntax is incorrect

C. autorestart should be false to start program

D. Log files are missing

Solution

1. Step 1: Check autostart setting

   autostart=false means Supervisor will NOT start the program automatically when it launches.

2. Step 2: Understand effect on program start

   Because autostart is false, the program must be started manually; this explains why it does not start automatically.

3. Final Answer:

   autostart is set to false, so program won't start on Supervisor launch -> Option A

4. Quick Check:

   autostart=false means no auto start = D [OK]

Hint: autostart=false disables automatic program start [OK]

Common Mistakes:

• Confusing autorestart with autostart
• Assuming command syntax is wrong without checking
• Thinking missing logs stop program start

5. You want Supervisor to run two programs, app1.py and app2.py, but only restart app2.py if it crashes. Which config setup is correct?

hard

A. [program:app1]
command=python3 /home/pi/app1.py
autostart=false
autorestart=true

[program:app2]
command=python3 /home/pi/app2.py
autostart=true
autorestart=false

B. [program:app1]
command=python3 /home/pi/app1.py
autostart=true
autorestart=false

[program:app2]
command=python3 /home/pi/app2.py
autostart=true
autorestart=true

C. [program:app1]
command=python3 /home/pi/app1.py
autostart=true
autorestart=true

[program:app2]
command=python3 /home/pi/app2.py
autostart=false
autorestart=true

D. [program:app1]
command=python3 /home/pi/app1.py
autostart=false
autorestart=false

[program:app2]
command=python3 /home/pi/app2.py
autostart=false
autorestart=false

Solution

1. Step 1: Identify requirements for app1 and app2

   app1 should run automatically but NOT restart on crash (autorestart=false). app2 should run automatically and restart on crash (autorestart=true).

2. Step 2: Match config options to requirements

   [program:app1] command=python3 /home/pi/app1.py autostart=true autorestart=false [program:app2] command=python3 /home/pi/app2.py autostart=true autorestart=true sets autostart=true for both, autorestart=false for app1, and autorestart=true for app2, matching the requirements exactly.

3. Final Answer:

   [program:app1] command=python3 /home/pi/app1.py autostart=true autorestart=false [program:app2] command=python3 /home/pi/app2.py autostart=true autorestart=true -> Option B

4. Quick Check:

   app1 no restart, app2 restart = A [OK]

Hint: Set autorestart true only for programs needing auto-restart [OK]

Common Mistakes:

• Setting autostart false prevents program from running automatically
• Confusing autostart and autorestart settings
• Setting autorestart true for programs that shouldn't restart