This is a systemd password agent that reads password from removable drive, e.g. USB thumb.
Get the sources and build them with make. iniParser library is required.
On Gentoo iniParser can be installed with emerge -av1 dev-libs/iniparser.
If the build succeeds, you'll get systemd-ask-password-remdev executable.
Copy it to some directory which is available during boot, e.g. /usr/local/bin.
Copy two provided systemd unit files (*.path and *.service) to /etc/systemd/system and edit the *.service one:
- in the Requires and After lines specify the device unit corresponding to your removable drive
- in the ExecStart line specify path to
systemd-ask-password-remdev, the removable device, its filesystem type and path to password file on the device
Execute systemctl enable systemd-ask-password-remdev.path.
Gentoo Linux, GCC 4.7.3, systemd 208