Lock Screen from root shell

Question

I try to set up a script to lock my screen when I unplug my Yubikey.

At the moment I am stuck with the correct way to send the command to lightdm.

That were my tries:

smiddy@3000-N200:~$ sudo su -
[sudo] password for smiddy: 
root@3000-N200:~# dm-tool lock
Not running inside a display manager, XDG_SEAT_PATH not defined
root@3000-N200:~# /bin/su smiddy -c "dm-tool lock"
Not running inside a display manager, XDG_SEAT_PATH not defined
root@3000-N200:~# $XDG_SEAT_PATH
root@3000-N200:~# echo $XDG_SEAT_PATH

root@3000-N200:~# XDG_SEAT_PATH="/org/freedesktop/DisplayManager/Seat0"
root@3000-N200:~# echo $XDG_SEAT_PATH
/org/freedesktop/DisplayManager/Seat0
root@3000-N200:~# dm-tool lock
Not running inside a display manager, XDG_SEAT_PATH not defined
root@3000-N200:~# /bin/su smiddy -c "dm-tool lock"
Not running inside a display manager, XDG_SEAT_PATH not defined
root@3000-N200:~# su smiddy
smiddy@3000-N200:/root$ dm-tool lock
Not running inside a display manager, XDG_SEAT_PATH not defined

It seems that the dm-tool does not recognize the active seat. But when I just fire up a terminal an send dm-tool lock the screen is locked.

Answer 1

To set an env var, you need to use export:

export XDG_SEAT_PATH="..."

printenv command prints env variables.