My fingerprint sensor works fine, in fact it works quite well except when it comes to SDDM. I use fprintd and systemd.

I have looked online for solutions, one involved changing some code in a systemd service, the only problem is I use NixOS. (for those who don't know, NixOS makes most of the root folder read only for the purpose of making everything editable from one file). I don't know how to change an existing service inside of NixOS.

to replicate my situation I have a fresh install of NixOS plasma5 from Here. I then moved to the unstable channel and upgraded my system to plasma6 with this guid. and lastly I enabled fprintd. for my sensor I didn't need to specify any drivers but your experience may vary.

Does anyone know how to fix this? and if not, does anyone know how to edit or append to an already existing systemd service inside of NixOS? also, if possible, I would like to only use the config file. you should probably also know I have no experience using flakes or the nix-env command.

any help would be appreciated, thank you.

1 Answer 1


to login via sddm Make sure that your fingerprint is registered before making these changes. Fingerprint support is not completely working properly yet, and it seems logging in with only a password no longer works using this method.

In order to use either a password or a fingerprint add the following to the top of /etc/pam.d/sddm

auth            [success=1 new_authtok_reqd=1 default=ignore]   pam_unix.so try_first_pass likeauth nullok
auth            sufficient      pam_fprintd.so

source for sddm login

  • I don't have a folder at /etc/pam.d/ called system-local-login . I do have ones called login, kde-fingerprint, systemd-user, sddm, and sddm-autologin. also, if it wasn't clear before, my fingerprint sensor works great with everything after SDDM so are you telling me to remove and reinstall fprintd or was I not clear?
    – MatsuNoKi
    Commented Apr 8 at 3:45
  • @MatsuNoKi made it shorter Commented Apr 8 at 3:52
  • I also forgot to remind you that even if that file did exist, I use NixOS meaning most of the root folder is read only. I saw your new suggestion of instead editing the sddm file but since it is located within the root folder... I have tried it and it is read only.
    – MatsuNoKi
    Commented Apr 8 at 3:57

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