Process management with supervisor in Raspberry Pi - Mini Project: Build & Apply

Process Management with Supervisor on Raspberry Pi

📖 Scenario: You have a Raspberry Pi running several small programs. You want to make sure these programs start automatically and keep running even if they crash. Supervisor is a tool that helps manage these programs easily.

🎯 Goal: You will create a Supervisor configuration file to manage a simple Python script as a process. You will set up the configuration, start Supervisor, and check the process status.

📋 What You'll Learn

Create a Supervisor configuration file for a Python script

Set up a program section with the correct command and settings

Reload Supervisor to apply the configuration

Check the status of the managed process

💡 Why This Matters

🌍 Real World

Supervisor helps keep important programs running on devices like Raspberry Pi without manual restarts.

💼 Career

Understanding process management with Supervisor is useful for system administrators and developers managing services on Linux-based systems.

1

Create a simple Python script

Create a Python script called hello.py that prints "Hello from Supervisor!" and then waits for 60 seconds. Write exactly these two lines in the script.

Raspberry Pi

# Create hello.py with the required two lines
# Your code here

Hint

Use print() to show the message and time.sleep(60) to pause.

2

Create Supervisor configuration file

Create a Supervisor configuration file named hello.conf with a [program:hello] section. Set command=python3 /home/pi/hello.py, autostart=true, and autorestart=true exactly as shown.

Raspberry Pi

print("Hello from Supervisor!")
import time
time.sleep(60)

# Create hello.conf with the program section and settings
# Your code here

Hint

The file must start with [program:hello] and include the exact command and options.

3

Reload Supervisor to apply configuration

Run the command sudo supervisorctl reread followed by sudo supervisorctl update to reload Supervisor and apply the new hello.conf configuration.

Raspberry Pi

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

# Run commands to reload Supervisor
# Your code here

Hint

Use these two commands exactly to reload Supervisor's configuration.

4

Check the status of the managed process

Run the command sudo supervisorctl status hello to check if the hello program is running under Supervisor.

Raspberry Pi

sudo supervisorctl reread
sudo supervisorctl update

# Check the status of hello program
# Your code here

Hint

This command shows if the program is running or stopped.

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