Unable to access second start up disk

Crowsfeet48 wrote:

Tried the PRAM reset. No luck.

Do you mean the traditional method mentioned in the Apple article I linked? If so, did it ignore the keys or were you able to hear the startup chime multiple times if you held the keys down for a minute?

(Note, I've never used the terminal. Do I simply type in that code?)

Yes, just type it as is, or copy & paste it into the Terminal app. Press the "Return" key after typing the command (or pasting it) to execute the command. Re-read the rest of my instructions & notes in my previous post on what to do next after executing the command.

I'll try the rEFind, I'm not a code guy but I'll give it a shot.

I believe the rEFInd developer has good instructions on how to launch & use the rEFInd installer script. It has been some time since I have reviewed those instructions. I think you will be impressed with the boot menu once rEFInd has been installed & configured as the default Startup Disk.

Are you using a wired USB keyboard? If not, then it is possible the wireless keyboard is not being recognized soon enough to process the special startup keys.

Try a PRAM Reset. Since you are having issues accessing the Option Boot screen, then it will likely affect being able to perform a PRAM Reset. There is another method using the command line in the Terminal app to clear the PRAM (aka NVRAM). Here is the command to use:

sudo  nvram  -c

This command will prompt you for your admin password. Nothing will appear on the screen as you type the password. Press the "Return" key to submit the password. You may see a permission denied message for certain settings which is Ok as long as there are no errors for the command itself. Reboot the computer so it will pull the default PRAM settings which hopefully will give you access to the special startup keys again.

Disconnect all other external devices including your external Catalina boot drive to see whether you can access the Option Boot screen. If this works, then it may indicate a problem with your external drive causing a problem.

You may want to consider using rEFInd which is a graphical boot manager which would make switching between the two operating systems very easy. You will want to install rEFInd to the internal boot drive so it is always available. All the rEFInd installer script does is create & store the rEFInd software on an existing hidden EFI (aka ESP) partition so that the system firmware will see the rEFInd bootloader as a valid boot option. AFAIK rEFInd doesn't remain running within macOS after the installer finishes (unless you run it again yourself). I believe the rEFInd installer script will work with Mavericks.