Example to boot from `dev/disk0s3` once:
sudo /usr/sbin/bless --device /dev/disk0s3 --setBoot --legacy --nextonly
More information:
https://hints.macworld.com/article.php?story=201106012209257...
List the available startup volumes:
sudo systemsetup -liststartupdisks
Set startup partition:
sudo systemsetup -setstartupdisk /Volumes/MyPartition
https://krypted.com/mac-security/dont-use-bless-to-change-st...