What is Supervisor and how to set it up

Supervisor is a process manager that simplifies running and monitoring long-lived programs. It's particularly useful for keeping background processes alive on a VPS or dedicated server.

Supervisor has two components: supervisord — the server process that spawns and monitors child processes — and supervisorctl, a command-line and web interface for managing supervisord.

Installation

On Debian and Ubuntu, install Supervisor from the standard repository:

apt-get install supervisor

Configuration

The configuration file is located at /etc/supervisor/supervisord.conf on Debian and Ubuntu, or /etc/supervisord.conf on other distributions.

To add a process, define a program section in the configuration file:

[program:worker]
command=/usr/bin/php /var/www/worker.php
stdout_logfile=/var/log/worker.log
autostart=true
autorestart=true
user=www-data
stopsignal=KILL
numprocs=1

Parameter descriptions:

• [program:worker] — the process name.
• command — path to the executable.
• stdout_logfile — path to the log file for console output.
• autostart — start the process automatically when Supervisor starts.
• autorestart — restart the process automatically if it crashes.
• user — the user account the process runs under.
• stopsignal — the signal sent to stop the process.
• numprocs — the number of process instances to run.

After updating the configuration, restart Supervisor:

/etc/init.d/supervisor restart

Web interface

Supervisor includes a built-in web interface for monitoring and controlling processes. To enable it, uncomment and configure the [inet_http_server] section in the configuration file:

[inet_http_server]
port=127.0.0.1:9001
username=some_user_name
password=some_password

Event monitoring

Supervisor has a built-in event listener mechanism for receiving error notifications. Here's an example configuration that sends an alert when memory usage exceeds a threshold:

[eventlistener:memmon]
command=memmon -a 200MB -m error@site.com
events=TICK_60