You can change a remote computer’s startup disk using SSH.
Log in to the remote computer using SSH, then enter:
$ sudo systemsetup -liststartupdisksLog in to the remote computer using SSH, then enter:
$ sudo systemsetup -setstartupdisk pathReplace path with the path to an available startup disk on the remote computer. If a startup disk name contains spaces or other special characters, you may need to precede each with the backslash escape “\” character.
To view the current settings for the startup disk enter:
$ sudo systemsetup -getstartupdisk