# Hafnium RAM disk

Hafnium expects to find the following files in the root directory of its RAM
disk:

*   `manifest.dtb` -- configuration file in DeviceTree format (required)
*   kernels for the VMs, whose names are described in the manifest (optional)
*   initrd of the primary VM, whose name is described in the manifest (optional)

The `manifest.dtb` must be the first file in the RAM disk, to ensure that it is
properly aligned. Hafnium will not be able to read it if it is not aligned to a
4 byte boundary.

Follow the [preparing Linux](PreparingLinux.md) instructions to produce
`vmlinuz` and `initrd.img` for a basic Linux primary VM.

## Create a RAM disk for Hafnium

Assuming that a subdirectory called `initrd` contains the files listed in the
previous section, we can build `initrd.img` with the following command:

```shell
cd initrd; echo -e "./manifest.dtb\n$(find . -type f -not -name manifest.dtb)" | cpio -o -v > ../initrd.img; cd -
```