How to write startup script for systemd

There are mainly two approaches to do that:

• If you have to run a script, you don't convert it but rather call the script through a systemd service.

Therefore you need two files: the script and the "service" file. Let's say your script is called vgaoff. Place your script in /usr/lib/systemd/scripts, make it executable. Then create a new service file in /usr/lib/systemd/system (a plain text file, let's call it vgaoff.service). So this is the location of your files:

1. the script: /usr/lib/systemd/scripts/vgaoff
2. the service: /usr/lib/systemd/system/vgaoff.service

Now you have to edit the service file. Its content depends on how your script works:

If vgaoff just powers off the gpu, e.g.:

exec blah-blah pwrOFF etc 

then the content of vgaoff.service should be:

[Unit]
Description=Power-off gpu

[Service]
Type=oneshot
ExecStart=/usr/lib/systemd/scripts/vgaoff

[Install]
WantedBy=multi-user.target

If vgaoff is used to power off the GPU and also to power it back on, e.g.:

start() {
  exec blah-blah pwrOFF etc
}

stop() {
  exec blah-blah pwrON etc
}

case $1 in
  start|stop) "$1" ;;
esac

then the content of vgaoff.service should be:

[Unit]
Description=Power-off gpu

[Service]
Type=oneshot
ExecStart=/usr/lib/systemd/scripts/vgaoff start
ExecStop=/usr/lib/systemd/scripts/vgaoff stop
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target

Once you have the files in place and configured you can enable the service:

systemctl enable vgaoff.service

It should then start automatically after rebooting the machine.

• For the most trivial cases, you can do without the script and execute a certain command directly through the .service file:

To power off:

[Unit]
Description=Power-off gpu

[Service]
Type=oneshot
ExecStart=/bin/sh -c "echo OFF > /whatever/vga_pwr_gadget/switch"

[Install]
WantedBy=multi-user.target

To power off & on:

[Unit]
Description=Power-off gpu

[Service]
Type=oneshot
ExecStart=/bin/sh -c "echo OFF > /whatever/vga_pwr_gadget/switch"
ExecStop=/bin/sh -c "echo ON > /whatever/vga_pwr_gadget/switch"
RemainAfterExit=yes

[Install]
WantedBy=multi-user.target