H. Nikolaus Schaller wrote on Thu, Jan 03, 2019:
root@letux:~# phosh 2018-12-21 18:54:53 - [rootston/config.c:370] Configured output Virtual-1 with mode 720x1440@0.000000 2018-12-21 18:54:53 - [rootston/config.c:370] Configured output X11-1 with mode 768x1024@0.000000 2018-12-21 18:54:53 - [backend/session/logind.c:363] Failed to get seat id: No data available 2018-12-21 18:54:53 - [backend/session/direct.c:159] Could not get current tty number: Inappropriate ioctl for device 2018-12-21 18:54:53 - [backend/session/session.c:76] Failed to load session backend 2018-12-21 18:54:53 - [backend/backend.c:250] Failed to start a DRM session 2018-12-21 18:54:53 - [rootston/main.c:26] could not start backend
I don't have any device to play with and never tried phosh, but the wlroots logind code here is pretty trivial, sd_session_get_seat() failed so looking at systemd code it looks like /run/systemd/sessions/<whatever your session is> doesn't have a SEAT value i.e. `loginctl list-sessions` would not match up your current session with a systemd "seat".
There can be many reasons for that but I'd wager something is missing in your pam, is there a line 'session optional pam_systemd.so' in the pam used at login?
Basically you need to make systemd understand that logging in from the tty means having physial access, with the seat lies all kinds of permissions to use the graphic cards and input devices etc.