By Alex Garnett

Senior DevOps Technical Writer

In many VPS environments, it is often the case that you will have a number of small programs that you want to run persistently, whether these are small shell scripts, Node.js apps, or any large-sized packages.

Usually, external packages are supplied with a unit file that allows them to be managed by an init system such as systemd, or packaged as docker images which can be managed by a container engine. However, for software that isn’t well-packaged, or for users who would prefer not to interact with a low-level init system on their server, it is helpful to have a lightweight alternative.

Supervisor is a process manager which provides a singular interface for managing and monitoring a number of long-running programs. In this tutorial, you will install Supervisor on a Linux server and learn how to manage Supervisor configurations for multiple applications.

To complete this guide, you will need:

Begin by updating your package sources and installing Supervisor:

The supervisor service runs automatically after installation. You can check its status:

You should receive the following output:

Now that we have Supervisor installed, we can look at adding our first programs.

A best practice for working with Supervisor is to write a configuration file for every program it will handle.

All programs run under Supervisor must be run in a non-daemonising mode (sometimes also called ‘foreground mode’). If, by default, your program automatically returns to the shell after running, then you may need to consult the program’s manual to find the option to enable this mode, or Supervisor will not be able to properly determine the status of the program.

In order to demonstrate Supervisor’s functionality, we’ll create a shell script that does nothing other than produce some predictable output once a second, but will run continuously in the background until it is manually stopped. Using nano or your favorite text editor, open a file called idle.sh in your home directory:

Add the following contents:

Save and close the file. If you are using nano, press Ctrl+X, then when prompted, Y and Enter.

Next, make your script executable:

The per-program configuration files for Supervisor programs are located in the /etc/supervisor/conf.d directory, typically running one program per file and ending in .conf. We’ll create a configuration file for this script, as`/etc/supervisor/conf.d/idle.conf:

Add these contents:

We’ll review this line by line:

The configuration begins by defining a program with the name idle and the full path to the program:

The next two lines define the automatic behavior of the script under certain conditions.

The autostart option tells Supervisor that this program should be started when the system boots. Setting this to false will require a manual start following any system shutdown.

autorestart defines how Supervisor should manage the program in the event that it exits:

The final two lines define the locations of the two main log files for the program. As suggested by the option names, stdout and stderr will be directed to the stdout_logfile and stderr_logfile locations respectively. The specified directories must already exist, as Supervisor will not attempt to create any missing directories.

The configuration we have created here is a minimal template for a Supervisor program. The Supervisor documentation lists many more optional configuration options that are available to tune how programs are run.

Once our configuration file is created and saved, we can inform Supervisor of our new program through the supervisorctl command. First we tell Supervisor to look for any new or changed program configurations in the /etc/supervisor/conf.d directory with:

Followed by telling it to enact any changes with:

Any time you make a change to any program configuration file, running the two previous commands will bring the changes into effect.

At this point our program should now be running. We can check its output by looking at the output log file:

Next, we’ll cover some other usage of Supervisor.

Beyond running programs, you will want to stop, restart, or see their status. The supervisorctl program, which we used in Step 2, also has an interactive mode which we can use to control our programs.

To enter the interactive mode, run supervisorctl with no arguments:

supervisorctl will initially print the status and uptime of all configured programs, followed by its command prompt. Entering help will reveal all of its available commands:

You can start or stop a program with the associated commands followed by the program name:

Using the tail command, you can view the most recent entries in the stdout and stderr logs for your program:

Using status you can view again the current execution state of each program after making any changes:

Finally, you can exit supervisorctl with Ctrl+C or by entering quit into the prompt:

In this tutorial, you learned how to install and manage Supervisor. As mentioned, Supervisor is very lightweight by modern standards, but it continues to be well-maintained, and it can be a useful tool for smaller deployments. It is also a low-maintenance and self-contained way of generating logs as a component part of a larger deployment.

If you’re running multiple small apps that need to be web accessible, you may also want to read about configuring Nginx as a reverse proxy, which is another fundamental component of small, reusable deployments.

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Senior DevOps Technical Writer

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Hi there, I was trying to run this tutorial in a docker context and was running into errors:

https://stackoverflow.com/questions/22450171/attempting-to-recreate-supervisor-tutorial-in-docker-running-into-error-permis

Any thoughts on why?

Great tutorial! One more thing to add would be “directory=[some directory]”, which causes a change directory to occur before running your command. In my case this helped resolve relative paths in my application.

Thanks!

This is awesome! So much nicer than having to fiddle with init.d files

Is there an easy way to take control of a process that supervisor started? Like for example when running a game server that might require occasional console input.

When you install supervisor like this it runs as root :

Is this correct or should instruction be added to the article to advise users to update Supervisor configuration file and add a non root user?

Had error:

When running:

had to add:

on top of /etc/supervisor/conf.d/idle.conf

This comment has been deleted

Do I have to do something special in the config file to stop it from trying to restart an already running service?

for example tail stdout.log shows this over and over:

“Service admin is already running Service admin is already running Service admin is already running Service admin is already running”

Thanks for the great tutorial. The supervisord ppa that ships with ubuntu 14.04 LTS is an old 3.0b version. The current latest stable version is 3.3.3 and it fixes some useful things (works better with ansible for example). Could you provide suggestions on a neat way of updating the ppa? Thanks!

Thank you, good explanation.

Having setup my conf file, and launch sudo supervisorctl reload and sudo supervisorctl start all, I got the following errors:

Here is my /etc/supervisor/leanote.conf:

Please help.