changedetection.py exits with status=2/INVALIDARGUMENT when using --user-data-dir via systemd (Selenium fallback)

[tamarw]

Environment:

• Version: Latest main branch via git pull as of approx April 29, 2025.
• Installation Method: git clone, dependencies installed via pip3 install -r requirements.txt
• Operating System: Linux Fedora Core 40
• Python Version: Python 3.12
• Deployment: Running via systemd service as a regular user
• Browser Fetcher Context: Using local chromedriver (confirmed running on localhost:9515), accessed via WEBDRIVER_URL environment variable because application logs indicate "Falling back to selenium as fetcher".

Bug Description:

When attempting to run changedetection.io as a systemd service with the --user-data-dir argument specified in ExecStart (to provide unique browser profiles using systemd's %t), the main changedetection.py process exits immediately after starting. Systemd logs show the process exiting with code=exited, status=2/INVALIDARGUMENT. This prevents the service from starting successfully and makes the web UI (port 5000) inaccessible.

This occurs even when the specified --user-data-dir path points to a valid location (e.g., /path/to/userhome/app/data/profile-%t) where the user has write permissions, and even if the target profile directory is freshly created and empty.

Steps to Reproduce:

• Configure a systemd service unit similar to the snippet below.
• Ensure chromedriver is available and the WEBDRIVER_URL environment variable points to it.
• Run sudo systemctl daemon-reload.
• Run sudo systemctl restart your-service-name.service.
• Check logs using sudo journalctl -u your-service-name.service.

Logs & Evidence:

1. Systemd Log Snippet showing failure:

Apr 29 02:18:11 [hostname] systemd[1]: Started changedetection.service - Changedetection.io.
Apr 29 02:18:12 [hostname] python3[PID]: 2025-04-29 02:18:12.304 | DEBUG    | changedetectionio.content_fetchers:<module>:61 - Falling back to selenium as fetcher
Apr 29 02:18:12 [hostname] python3[PID]: 2025-04-29 02:18:12.679 | INFO     | changedetectionio.flask_app:<module>:83 - System locale default is ('en_US', 'UTF-8')
# Note: Strange usage line printed here instead of web server startup
Apr 29 02:18:12 [hostname] python3[PID]: backend.py -s SSL enable -h [host] -p [port] -d [datastore path] -l [debug level - TRACE, DEBUG(default), INFO, SUCCESS, WARNING, ERROR, CRITICAL]
# Process exits immediately with code 2
Apr 29 02:18:12 [hostname] systemd[1]: changedetection.service: Main process exited, code=exited, status=2/INVALIDARGUMENT
Apr 29 02:18:12 [hostname] systemd[1]: changedetection.service: Failed with result 'exit-code'.
# ... (Service enters restart loop and eventually fails) ...
Apr 29 02:18:20 [hostname] systemd[1]: Failed to start changedetection.service - Changedetection.io.

2. Broken --help Output: Running --help directly on the command line also fails when the Selenium fallback occurs, printing the same misleading backend.py line and exiting, instead of displaying help.

Bash

$ /usr/bin/python3 /path/to/userhome/app/changedetection.py --help
2025-04-29 02:21:57.321 | DEBUG    | changedetectionio.content_fetchers:<module>:61 - Falling back to selenium as fetcher
2025-04-29 02:21:57.643 | INFO     | changedetectionio.flask_app:<module>:83 - System locale default is ('en_US', 'UTF-8')
backend.py -s SSL enable -h [host] -p [port] -d [datastore path] -l [debug level - TRACE, DEBUG(default), INFO, SUCCESS, WARNING, ERROR, CRITICAL]
$ # Exits immediately

3. Non-existent backend.py: The backend.py script referred to in the erroneous output does not exist in the repository structure.

4. Consequence of Workaround: If --user-data-dir is removed from ExecStart, the service does start and port 5000 is accessible. However, this leads back to the expected browser profile locking errors during concurrent checks:

Exception: Message: session not created: probably user data directory is already in use, please specify a unique value for --user-data-dir argument, or don't use --user-data-dir Stacktrace: #0 0x55c2eca1cb8e <unknown> #1 0x55c2ec3f691b <unknown> ... (etc) ...

Expected Behavior:

The changedetection.py script should start successfully via systemd when the --user-data-dir argument is provided, bind to the specified host/port (e.g., 5000), and remain running to serve the web UI and perform checks using unique browser profiles based on the %t specifier. The --help argument should also function correctly.

Relevant Systemd Configuration Snippet:

Ini, TOML

[Service]
User=[username]
WorkingDirectory=/path/to/userhome/app/
# This ExecStart line causes the exit code 2 / INVALIDARGUMENT failure
ExecStart=/usr/bin/python3 /path/to/userhome/app/changedetection.py --user-data-dir=/path/to/userhome/app/data/profile-%t --host 0.0.0.0 --port 5000
Restart=always
# This environment variable is set to use local chromedriver
Environment=WEBDRIVER_URL=http://localhost:9515

[dgtlmoon]

--user-data-dir is not a valid option, it's even in your output logs that this is not a valid option

Use -d /tmp/data

Apr 29 02:18:12 [hostname] python3[PID]: backend.py -s SSL enable -h [host] -p [port] -d [datastore path] -l [debug level - TRACE, DEBUG(default), INFO, SUCCESS, WARNING, ERROR, CRITICAL]
# Process exits immediately with code 2
Apr 29 02:18:12 [hostname] systemd[1]: changedetection.service: Main process exited, code=exited, status=2/INVALIDARGUMENT
Apr 29 02:18:12 [hostname] systemd[1]: changedetection.service: Failed with result 'exit-code'.

[tamarw]

Thanks, so much for using AI to help me troubleshoot and structure my ask.

So how does one work around this issue? I've spent way too much time trying to figure it out.

Thanks for the fast reply.

Exception: Message: session not created: probably user data directory is already in use, please specify a unique value for --user-data-dir argument, or don't use --user-data-dir Stacktrace: #0 0x55c2eca1cb8e <unknown> #1 0x55c2ec3f691b <unknown> #2 0x55c2ec430a7c <unknown> #3 0x55c2ec42acf7 <unknown> #4 0x55c2ec47beae <unknown> #5 0x55c2ec47b403 <unknown> #6 0x55c2ec46c5a3 <unknown> #7 0x55c2ec4383e7 <unknown> #8 0x55c2ec4390c1 <unknown> #9 0x55c2ec9e91da <unknown> #10 0x55c2ec9ec4f7 <unknown> #11 0x55c2ec9ebf88 <unknown> #12 0x55c2ec9ec9a5 <unknown> #13 0x55c2ec9d3156 <unknown> #14 0x55c2ec9ecd12 <unknown> #15 0x55c2ec9bb68a <unknown> #16 0x55c2eca0b2d5 <unknown> #17 0x55c2eca0b4f7 <unknown> #18 0x55c2eca1b5b5 <unknown> #19 0x7fd3feba7088 start_thread #20 0x7fd3fec2af8c __clone3

[dgtlmoon]

@tamarw I'm sorry I dont appreciate being offended by being called "AI", I spent my own time, for free, for you, to help you, so you can use software that is free for you to use, that was written by me when I should have been spending time with my family

So how does one work around this issue? I've spent way too much time trying to figure it out.

"
Exception: Message: session not created: probably user data directory is already in use, please specify a unique value for --user-data-dir argument, or don't use --user-data-dir Stacktrace: #0 0x55c2eca1cb8e #1 0x55c2ec3f691b #2 0x55c2ec430a7c #3 0x55c2ec42acf7 #4 0x55c2ec47beae #5 0x55c2ec47b403 #6 0x55c2ec46c5a3 #7 0x55c2ec4383e7 #8 0x55c2ec4390c1 #9 0x55c2ec9e91da #10 0x55c2ec9ec4f7 #11 0x55c2ec9ebf88 #12 0x55c2ec9ec9a5 #13 0x55c2ec9d3156 #14 0x55c2ec9ecd12 #15 0x55c2ec9bb68a #16 0x55c2eca0b2d5 #17 0x55c2eca0b4f7 #18 0x55c2eca1b5b5 #19 0x7fd3feba7088 start_thread #20 0x7fd3fec2af8c __clone3
"

--user-data-dir is not from changedetection.io , it is from playwright, selenium or others

Since you didnt attach your systemd setup config files i cannot help you, this from something you are doing custom, we do not yet have an official systemd recipe

[dgtlmoon]

How is selenium being started? I do not see in what you've pasted that your config is starting selenium

you are pasting the startup script for changedetection.io but the error is coming from your selenium startup, this error text does not exist in changedetection

[tamarw]

Hi, I didn't reply in the nested thread as I should've. I replied below; not sure if you saw it. I created a general systemd startup service, but I assume I can tweak it a bit. It might also solve the other question I posted; I think these are mostly JavaScript loading concerns.

I appreciate your help. Really, I do. Serious kudos on a super awesome app.

[tamarw]

Sorry you thought I was referring to YOU as AI. I wouldn't call a creator of excellent software AI. But to save you the trouble, that's where I started my troubleshooting. I've spent probably two days over maybe 18 hours to guide me here. After what can probably be more than 400 pages printed out across ChatGPT and Gemini, I have not gotten an answer.

Are you seeing anything here that might trigger it?

[Unit]
Description=Changedetection.io
After=network.target
[Service]                                                                                       User=ne
WorkingDirectory=/home/me/changedetection.io
#ExecStart=/usr/bin/python3 /home/me/changedetection.io/changedetection.py
ExecStart=/usr/bin/python3 /home/me/changedetection.io/changedetection.py -d /tmp/data/profile-%t --host 0.0.0.0 --port 5000                                                                 Restart=always
Environment=WEBDRIVER_URL=http://localhost:9515
#Environment=CHROME_BROWSER_COMMAND=google-chrome --no-sandbox --disable-dev-shm-usage --user-data-dir=/tmp/chrome-profile-%t
[Install]                                                                                       WantedBy=multi-user.target