Following tips i got from https://www.linuxbabe.com/linux-server/how-to-enable-etcrc-local-with-systemd
Log into your hifiberryos with ssh
Create rc-local.service
nano /etc/systemd/system/rc-local.service
Then add the following content to it.
[Unit] Description=/etc/rc.local Compatibility ConditionPathExists=/etc/rc.local [Service] Type=forking ExecStart=/etc/rc.local start TimeoutSec=0 StandardOutput=tty RemainAfterExit=yes SysVStartPriority=99 [Install] WantedBy=multi-user.target
Save and close the file.
Now create rc.local
nano /etc/rc.local
Add the following content to it.
#!/bin/sh -e
#
# rc.local
#
# This script is executed at the end of each multiuser runlevel.
# Ensure that the script will "exit 0" on success or any other
# value on error.
#
# To enable or disable this script, just change the execution
# bits.
#
# By default, this script does nothing.
echo 80 > /sys/class/backlight/rpi_backlight/brightness
exit 0
Save and close the file.
Hint: the higher the digit after "echo" the brighter the screen.
Max is 255
Then add execute permission to the file
chmod +x /etc/rc.local
After that, enable the service on system boot:
sudo systemctl enable rc-local
Start the service
systemctl start rc-local.service
You can check the status with
systemctl status rc-local.service
Then reboot the system
reboot
Now the 7" screen should start in your desired brightness.
