What does “booting a secondary […] device” mean? Either you boot from a device, and that makes it the primary device, or you boot off another device, in which

What does “booting a secondary […] device” mean? Either you boot from a device, and that makes it the primary device, or you boot off another device, in which case this is now the primary device. Or did you mean unlocking an encrypted device after unlocking and booting on the primary device? What does systemd have to do with that? Unless you want to type in the password manually every boot, you store the password (for the secondary device) on the primary device, add the password file to /etc/crypttab and be done with it, right?