# OS Description files
OS description files are used to detected host os for options such as `onlyon`.
## Where are these files located?
Bundled OSes are included (by `include_str!`) when kelpdot compiles. This YAML list can be found in [/src/config/oses.yaml](https://github.com/Woomymy/kelp/blob/main/src/config/oses.yaml).
You can add custom OSes in `/etc/kelpdot/os.yaml`.
### Describing an OS
```yaml
# /etc/kelpdot/os.yaml
- name: "superos" # Name for `onlyon`
file: "/" # if this file exist, we are **sure** the OS is O.K
priority: 0 # If multiple OSes are detected, the higher priority is more important. Use higher for childer distros
prettyname: "My super Gentoo-Based distro" # Pretty name of the OS (for printing)
submatches: [ "gentoo" ] # For exemple, mother distros
```