Is it possible to run an (inkyphat) python write script on raspi shutdown (systemd)

@peterG wrote:

Pi Zero W, Debian 9 (Raspbian)

I want to be able to run a last text-write to my inkyphat when I shutdown my Pi. So far, I’ve tried a number of systemd entries that allegedly work (for other people), but not for me. Here’s the systemd entry that almost worked:

[Unit] 
Description=runs only upon shutdown
Conflicts=reboot.target
After=network.target
[Service]
Type=oneshot
ExecStart=/bin/true
ExecStop=/bin/bash /usr/local/bin/shutdown_screen
RemainAfterExit=yes
[Install]
WantedBy=multi-user.target

And here’s shutdown_screen

#!/bin/bash
# send a shutdown message only at shutdown (not at reboot)    
/usr/bin/systemctl list-jobs | egrep -q 'reboot.target.*start' || inkywrite.py "time to go"

I know this gets run by systemd, but I can’t get the shutdown to wait until the write has completed before it shuts down. Can anyone advise me here as I’m going round in circles :(

edit: I got the above from https://unix.stackexchange.com/questions/284598/systemd-how-to-execute-script-at-shutdown-only-not-at-reboot#284773

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