| Most of the functionality that dracut implements are actually implemented |
| by dracut modules. Dracut modules live in modules.d, and have the following |
| structure: |
| |
| dracut_install_dir/modules.d/ |
| 00modname/ |
| install |
| check |
| <other files as needed by the hook> |
| |
| 00modname: The name of the module prefixed by a two-digit numeric sort code. |
| The numeric code must be present and in the range of 00 - 99. |
| Modules with lower numbers are installed first. This is important |
| because the dracut install functions (which install files onto |
| the initrd) refuse to overwrite already installed files. This makes |
| it easy for an earlier module to override the functionality of a |
| later module, so that you can have a distro or system specific |
| module override or modify the functionality of a generic module |
| without having to patch the mode generic module. |
| |
| install: dracut sources this script to install the functionality that a |
| module implements onto the initrd. For the most part, this amounts |
| to copying files from the host system onto the initrd in a controlled |
| manner. dracut supplies several install functions that are |
| specialized for different file types. Browse through dracut-functions |
| fore more details. dracut also provides a $moddir variable if you |
| need to install a file from the module directory, such as an initrd |
| hook, a udev rule, or a specialized executable. |
| |
| check: Dracut calls this program to check and see if a module can be installed |
| on the initrd. |
| |
| When called without options, check should check to make sure that |
| any files it needs to install into the initrd from the host system |
| are present. It should exit with a 0 if they are, and a 1 if they are |
| not. |
| |
| When called with -H, it should perform the same check that it would |
| without any options, and it should also check to see if the |
| functionality the module implements is being used on the host system. |
| For example, if this module handles installing support for LUKS |
| encrypted volumes, it should return 0 if all the tools to handle |
| encrpted volumes are available and the host system has the root |
| partition on an encrypted volume, 1 otherwise. |
| |
| Check may take additional options in the future. |
| We will most likely grow a module dependency checking system in the |
| near future, and check will need to handle a -d option when we do. |
| |
| Any other files in the module will not be touched by dracut directly. |
| |
| You are encouraged to provide a README that descrobes what the module is for. |