pam_systemd_loadkey - Read password from kernel keyring and set it as PAM authtok

pam_systemd_loadkey.so

pam_systemd_loadkey reads a NUL-separated password list from the kernel keyring, and sets the last password in the list as the PAM authtok.

The password list is supposed to be stored in the "user" keyring of the root user, by an earlier call to systemd-ask-password(1) with --keyname=. You can pass the keyname to pam_systemd_loadkey via the keyname= option.

This module is intended to be used when you use LUKS with a passphrase, enable autologin in the display manager, and want to unlock Gnome Keyring / KDE KWallet automatically. So in total, you only enter one password during boot.

You need to set the password of your Gnome Keyring/KWallet to the same as your LUKS passphrase. Then add the following lines to your display managers PAM config under /etc/pam.d/ (e.g. sddm-autologin):

.RS 4

-auth       optional    pam_systemd_loadkey.so
-session    optional    pam_gnome_keyring.so auto_start
-session    optional    pam_kwallet5.so auto_start
    

.RE

And add the following lines to your display managers systemd service file, so it can access roots keyring:

.RS 4

[Service]
KeyringMode=inherit
    

.RE

In this setup, early during the boot process, systemd-cryptsetup@.service(8) will ask for the passphrase and store it in the kernel keyring with the keyname "cryptsetup". Then when the display manager does the autologin, pam_systemd_loadkey will read the passphrase from the kernel keyring, set it as the PAM authtok, and then pam_gnome_keyring and pam_kwallet5 will unlock with the same passphrase.