This is MyCloud OS5 application wich allow to run scripts on boot
You need the packager mksapkg-OS5 from WD https://github.com/WDCommunity/wdpksrc
I package the app under Ubuntu 20.04 (x64) with the command line and using the template MyCloudEX2Ultra (please read documentation about mksapkg-OS5)
cd ./boot4shell
./mksapkg-OS5 -s -m MyCloudEX2Ultra
The resulting bin file will be generated at the parent folder of ./boot4shell remove the date stamp at the end of the file and keep the .bin extension (MyCloudEX2Ultra_boot4shell_0.0.1.bin)
Manually install the app from your WD Cloud ui then modify the boot.sh in the /mnt/HD/HD_a2/Nas_Prog/boot4shell folder. Once installed don't forget to activate the app