https://github.com/swagdevops/ylem

Another minimal init system for Unix/Linux containers
https://github.com/swagdevops/ylem

containers init init-system linux startup-process unix

Last synced: 8 days ago
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Another minimal init system for Unix/Linux containers

• Host: GitHub
• URL: https://github.com/swagdevops/ylem
• Owner: SwagDevOps
• License: gpl-3.0
• Created: 2017-05-21T20:55:17.000Z (over 7 years ago)
• Default Branch: master
• Last Pushed: 2024-03-01T16:54:03.000Z (9 months ago)
• Last Synced: 2024-04-22T14:47:29.609Z (7 months ago)
• Topics: containers, init, init-system, linux, startup-process, unix
• Language: Ruby
• Homepage:
• Size: 384 KB
• Stars: 1
• Watchers: 2
• Forks: 1
• Open Issues: 1
• Metadata Files:
  • Readme: README.md
  • License: LICENSE

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README

        


# Ylem ``/ˈiːlɛm/`` the primordial matter of the universe

## Principles

During the [Linux startup process](https://en.wikipedia.org/wiki/Linux_startup_process),

``ylem`` is intended to sequentially execute arbitrary "user scripts"

(alphabetically sorted). Moreover ``ylem`` provides [logging](#logging)

which facilitates startup __debugging__.

Startup scripts executed through ``ylem`` SHOULD be aimed to:

* create required files and directories

* setup users and permissions

* prepare the system to run deamons

For example, ``ylem`` COULD start

[``supervisor``](https://github.com/Supervisor/supervisor),

to manage daemons, as soon as the system is sufficiently ready.

Create an ``/etc/ylem/scripts`` directory and put your bootstraping scripts.

Then scripts are executed alphabetically sorted.

## Sample of use

In a ``Dockerfile``:

```

ENTRYPOINT ["dumb-init", "-c", "--", "ylem", "start", "--"]

CMD ["sleep", "infinity"]

```

## Configuration

The configuration uses a [YAML syntax](https://en.wikipedia.org/wiki/YAML)

and remains in ``/etc/#{progname}/config.yml``,

where ``progname`` is ``ylem``.

Furthermore configuration filepath can be set on the

CLI.

Available configuration keys are:

* ``scripts.path``


  where bootstraping scripts are stored


  default value is: ``/etc/#{progname}/scripts``

* ``logger.file``


  default value is: ``/var/log/#{progname}.log``

* ``logger.level``


  default value is: ``INFO`` (see: [Logger::Severity](https://ruby-doc.org/stdlib-2.1.0/libdoc/logger/rdoc/Logger/Severity.html))

* ``environment.file``


  default value is: ``/etc/environment``

  ([System-wide environment variables](https://help.ubuntu.com/community/EnvironmentVariables#System-wide_environment_variables))

Missing configuration keys use default values.

Configuration file can be: complete, partial or empty.



## Logging

Ylem provides its own logging mechanism, based on

[``Logger``](https://ruby-doc.org/stdlib-2.1.0/libdoc/logger/rdoc/Logger.html).

During its init process, each handled script is logged to ``logger.file``.

Depending on ``logger.level`` only the messages with a level greater or equal

will be published to the log file.

| Level         | Format          | Summary                             |

| ------------- | --------------- | ----------------------------------- |

| ``DEBUG``     | ``/"BEGIN"/``   | script started                      |

| ``INFO``      | ``/".*"/``      | script message echoed to ``STDOUT`` |

| ``WARN``      | ``/".*"/``      | script message echoed to ``STDERR`` |

| ``DEBUG``     | ``/"ENDED \[0\]/"``     | script ended (success)      |

| ``ERROR``     | ``/"ERROR \[[0-9]+\]"/``| script error                |

## Resources

* [Yelp/dumb-init: A minimal init system for Linux containers](https://github.com/Yelp/dumb-init)

* [Supervisor process control system for UNIX](https://github.com/Supervisor/supervisor)

* [``/sbin/my_init`` as seen in ``phusion/baseimage-docker``](https://github.com/SwagDevOps/baseimage-docker/blob/master/image/bin/my_init)

* [``runit`` - a UNIX init scheme with service supervision](http://smarden.org/runit/)