A Look at minit

The power on button

Sys-V init has long been the standard solution for booting. It's kind of easy to work with, it kind of works and everybody kind of knows it. However, being open minded, let's look at an alternative approach.

There are quite a few alternatives. All of them focus on improving boot times. This is accomplished by starting and running different processes simultaneously and asynchronously. Doing type of boot attempts to use all (more) parts of the hardware simultaneously and avoid having to wait for slow hardware.

In an embedded setting, one more factor to look for is keeping the footprint and number of processes down (each process comes with an overhead - albeit small).

One of the alternatives that I've looked at is minit by Felix von Leitner of diet-libc fame. What can it do? Well, the most basic feature is that it can start services and takes dependencies into account, e.g. it waits for the network to be up before it starts the web server. It also does respawning and handles ctrl+alt+delete.

Being the brain child of von Leitner, it is also minimalist (to the extreme?) and works with diet-libc. So, how does it work?

The configuration lives in /etc/minit, where each sub-directory contains one or services. Each service is configured from a number of symlinks and text files, all listed in detail in this howto. Basically, you create a symlink called "run" pointing at the program to start, a text file called "depends" with the names of any prerequisite services, an empty file called "respawn" if the service is to be respawned upon termination, and so on.

Having configured all your services, create a directory called "default" and add a depends file there listing your services. That will kickstart the system.

Image courtesy of http://www.flickr.com/photos/livingos/ / CC BY-SA 2.0. Original: at Flickr.

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