What is daemontools?
From the daemontools website:
daemontools is a collection of tools for managing UNIX services.
supervise monitors a service. It starts the service and restarts the service if it dies. Setting up a new service is easy: all supervise needs is a directory with a run script that runs the service.
At first when I was introduced to this tool at work, I thought “What a typical Linux-admin. FreeBSD’s rc. system is superior.” Despite my personal preferences, whatever software is used at work is what I have to use and learn to use, too. After getting a little more familiar with supervise, and installing it on a FreeBSD server, I was finally convinced that this may also have a place on FreeBSD machines.
Have you ever needed to know that a process is 100% sure to be running no matter what? Well, some of our applications need that extra little safety net, and you might too. Just right of the bat I can mention things like httpd, sshd, denyhosts, and syslog(-ng). While the theoretical risk of these applications crashing randomly and still being able to run again without any direct editing of some configuration file seems to be very low, in a production environment where loads are extremely high and all processes are pushed into a stage where their theoretical load-handling capacity is on the edge with what has practically been tested, this may happen to you – and you can’t afford the service being down until you figure out a way to fix it permanently.
Either way, if some application crashes in a recoverable manner, it’s most likely that either 1) supervise is still running and will try to revive the process or 2) your box is so broken, it doesn’t even matter that supervise is still running. It’s all about that extra little factor of reliability.
Convinced? Here’s the walkthrough