Thanks again. When I looked in biometric-authentication.service (as debian would have it) YES, the service restart option is set to Always however I noticed the next entry “RestartSec=0” so I tried setting it to 2 and rebooting. Not as many visible errors during the reboot but still a fail! Looking through the logs/displays etc I was further directed to - “journalctl -xe” which included the line = “PAM unable to dlopen(pam_biometric.so): /lib/x86_64-linux-gnu/security/pam_biometric.so: cannot open shared object file: No such file or directory” This is followed by the line “PAM adding faulty module: pam_biometric.so
" so it appears that the system attempts to repair the fault but rummaging around /lib/x86_64-linux-gnu/security there is no sign of a file “pam_biometric.so” which I think should be provided by the package " libpam-biometric_1.2.1-1_amd64.deb”. I believe I have all the prescribed libraries, all later versions than the minimum required, just no pam_biometric.so file.