Can I make my iMac boot from an OS on an external drive in safe mode?

I've searched all over the internet but I could not find a concrete answer to this question: I have an iMac that works fine and an external hard drive with OSX on it that I can boot too, but how can I boot to that drive in safe mode? Thanks!


Solution 1:

Just after your Mac is switched on:

First you select to boot from external drive by holding Option key and waiting for the list of disk choices.

Immediately after you select the external disk among boot options, you press and hold shift for safe boot.