This code is based on the following answer on Stack Overflow: https://stackoverflow.com/a/66686784 - I just changed the system() and cleaned up a few things.
It "fixes" the "Disk not Ejected Properly" issue on OSX. I use quotes because this isn't a permanent fix, I haven't patched OSX or anything of that sort. It's just an application that listens for OSX going to sleep and waking up and runs a system() call. This is extremely simple and rudimentary. It uses kIOMessageSystemWillSleep and kIOMessageSystemHasPoweredOn.
I really should be passing in the volume to eject & remount as command line arguments to the binary, or as a confgiuration. It is hardcoded for now. Change/Update the volume mount & disk in the source code to reflect your external disk.
Compile as follows:
gcc -o eam -framework IOKit -framework Cocoa eam.c
Run as follows:
./eam
Put your machine to sleep and then wake it up and you'll see similar output to the following:
☹ ./eam
Volume External on disk4s2 unmounted
Volume External on disk4s2 mounted
You may want to add a cron to ensure the binary is always running. If I get more time I'll add steps on how to do that.