On your computer, console.log (Node.js) and print (Python) show up on screen. A server has no screen, and the question is where they went. The short answer: on shared hosting, what the application writes goes to the Passenger log, the file you name in the Passenger log file field on the application screen; on a VPS it depends on what starts the application (PM2, systemd or Docker). Without that log, debugging an application is guesswork.
Where the log is, in each case
| Where it runs |
Where to look |
Command or place |
| Node.js or Python in cPanel |
In the file named in the Passenger log file field (on the “Setup Node.js App” or “Setup Python App” screen). |
Name a file inside the application folder, save, restart and repeat the request. Open it in File Manager, or in Terminal with tail -n 100 file.log. |
| VPS with PM2 |
In PM2’s logs. |
pm2 logs name or pm2 logs --lines 100 |
| VPS with systemd |
In the system journal. |
journalctl -u name -n 100, and -f to follow live |
| Docker |
In the container’s logs. |
docker logs name or docker compose logs -f service |
The site’s general error log is something else: it catches web server errors, not what your application writes. For that one, see errors 500, 403, 404 and 508.
Making it write logs you can read
| 1 |
Set the log file on the application screen (in cPanel), or use PM2’s, systemd’s or Docker’s (on a VPS).
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| 2 |
Write with meaning. Instead of console.log("here"), say what and with which value: the request’s method and path, the id of the record that was read, the whole error. Never write passwords, keys or personal data.
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| 3 |
In Python, avoid the delay. When output goes to a file, print may be held in memory and only appear later. Use print("text", flush=True), or the logging module, which writes at once. The environment variable PYTHONUNBUFFERED=1 has the same effect for the whole application.
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| 4 |
Restart and repeat. Make the request that fails and read the last lines: the cause is usually there. If the application will not even start, see the causes of the 503 error.
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A log with no limit ends up filling the disk. On a shared account, a file that grows every day uses space, and space is limited. Delete or archive now and then, or cap the size (in Python, the logging module’s RotatingFileHandler does that). On a VPS, the system journal and Docker’s logs grow too: see Docker filling the disk.
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Live, in Terminal. If the account has a terminal (the cPanel Terminal), tail -f file.log shows lines as they arrive: open the site in another tab and watch what appears. To leave, Ctrl+C.
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Have the log in front of you and cannot make sense of the last line? Send us the domain, the time of the error and that line.
Open a support ticket
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