Recognized files

systemd

• Units: .service, .socket, .timer, .path, .mount, .automount, .swap, .target, .device, .slice, and .scope
• Networkd: .network, .netdev, .link, .dnssd, and .dns-delegate
• Daemon configuration, .nspawn, .oomrule, repart, sysupdate, and drop-ins
• udev, hwdb, tmpfiles, sysusers, sysctl, modules-load, binfmt, presets, boot files, and systemd tables
• PCR lock, DNS record, and public userdb JSON

Quadlet and mkosi

Quadlet supports .artifact, .build, .container, .image, .kube, .network, .pod, and .volume.

mkosi supports its main file, drop-ins, presets, profiles, images, local files, tools, initrd, version, and UKI profiles.

Custom names

{
  "files.associations": {
    "deploy/my-unit": "systemd-unit"
  }
}

Use systemd.dialectAssociations for path-based choices and systemd.templateSuffixes for custom compound suffixes.