fingerprintd

Fingerprint daemon for the Fairphone 6 (milos, SM7635) on mainline Linux.

fingerprintd-core is a static library with no GLib, no libqcomtee and no system headers. Everything in it is a wire format or a state machine that was recovered by reverse-engineering, so all of it is pinned by tests that run on a dev box with no phone, no TEE and no sensor. The daemon shell holds everything that touches hardware.

fprintd-enroll -f right-index-finger user   ten stages, enroll-completed
fprintd-list user                            - #0: right-index-finger
fprintd-verify user   (wrong finger)         verify-no-match, on the first press
fprintd-verify user   (enrolled finger)      verify-match,    on the first press

Lock-screen unlock

Two routes, both on by default:

• PAM. The daemon provides fprintd, so a lock screen that runs pam_fprintd beside its password prompt unlocks by finger the usual way. Plasma's does (kde-fingerprint; the fingerprint-auth and postlogin services it needs are shipped here). Phosh's cannot: its PAM conversation answers every prompt with the password, so a fingerprint module in its stack would only stall the password behind the fingerprint timeout.
• Standby. While the session in front on its seat is locked and the display is on, the daemon runs a verify of its own and answers a match with logind's Session.Unlock, which Phosh honours. No verify runs while the display is off (an open verify polls the sensor at ~5 Hz; the display state comes from the backlight's bl_power or the panel's DRM dpms, and a device with neither is treated as always on). Any fprintd client takes precedence: a Claim cancels the standby verify, a Release re-arms it. Only fingers named in that session owner's map unlock, and the map is re-read at every arm, so a finger deleted while locked stops counting at once. Per-finger no-unlock rules apply here too, and every match is announced as FingerMatched for the session agent. --standby-unlock=off disables it.

Per-finger macros

The trustlet reports which finger matched, so a finger can mean more than "it was you". Two files, in two trust domains:

• ~/.config/fingerprintd/fingers.conf runs a command as you, in your session. This is how a finger opens an application.
• /etc/fingerprintd/actions.conf runs a command as root, and can mark a finger as one that never unlocks.

In your session: fingers.conf

# ~/.config/fingerprintd/fingers.conf
right-ring-finger    kde-open camera
left-index-finger    plasma-settings
left-thumb           sh -c 'notify-send "hello from a finger"'

• using these requires the fingerprintd-agent service to be running.

As root: actions.conf

# /etc/fingerprintd/actions.conf
# <finger>  [no-unlock]  [absolute command...]
right-ring-finger    /usr/local/bin/toggle-something
left-little-finger   no-unlock  /etc/fingerprintd/panic.sh
left-thumb           no-unlock

• no-unlock: the finger matches and the client is told it did not. PAM sees verify-no-match, the standby unlock stays locked. The command, if there is one, runs regardless.
• the command: an absolute path, run by root through /bin/sh -c with a fixed PATH and FINGERPRINTD_FINGER set to the finger's name, detached from the daemon with its stdio on /dev/null, so it may block or reboot the phone without stalling the sensor.
• a line needs at least one of the two, and a finger gets at most one line.
• editing this file requires a restart of the fingerprintd service before changes take effect.

Runtime dependencies

The focal64 trustlet is proprietary and is not in this repo. It is extracted from the device's own stock Android partition on first boot by the fp6-vendor-blobs mechanism, the same way other firmware in fp6-img is.

License

GPL-3.0-only - see LICENSE.

Funding

https://catcrafts.net/shop/donation - see FUNDING

Copyright

Copyright (C) 2026 Catcrafts® catcrafts.net