From the course: macOS for IT Administrators

Modifying the startup process - Mac OS Tutorial

From the course: macOS for IT Administrators

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Modifying the startup process

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- [Instructor] You can change what happens at boot time with modifier keys on the keyboard. Start up your Mac and hold down Command and V together. Hold them down until you see text on the screen. This is a great way to watch the booter and kernel load in real time, which can be helpful in troubleshooting boot problems. Unless your Mac has a retina display, in which you will need reading glasses. We used to be able to press Command and S together to enter single-user mode, but that's no longer possible. Instead, the recommended method to access a pre-booted Mac is to use the command line for administration and hold down Command-R at startup. This allows you to enter the Recovery partition. You then open Disk Utility and mount the file system. This asks you for a password if File Vault's enabled. Go ahead and enter it there. And then when it mounts, you open up Terminal from the Utilities menu and you should be able to enter whatever commands you may find necessary. Though some commands are not included in the Recovery partition. These boot interrupt process changes became a standard in late-2018 and continue today. So what if you see something other than what I've described? Well, if you see a spinning globe instead of the apple, your Mac has booted from the internet servers Apple has in place to to provide recovery data to Macs in distress. A minimal boot volume will be installed so you can use Recovery to reinstall the operating system. If you see a prohibitory symbol, the circle with a slash through it, that means the operating system cannot load the version of macOS on the hardware that you're running. Now that's in 10.14 and later, but that means the booter couldn't load the kernel for some reason, possibly because of kernel caches being messed up on 10.13 and earlier. So, depending on the version, different troubleshooting steps. A folder with a question mark means that the selected startup disk isn't available or doesn't contain a Mac operating system. Boot into Safe Mode if your Mac can find an OS to boot from, to delete caches and start up again. Safe Boot is accomplished by holding down the Shift key during boot and we've covered it in another movie. If the system starts during Safe Boot, it means the booter found problems to repair on the boot volume. The right thing to do is keep holding down that Shift button and wait. If it can, the booter will hand off to the kernel, which will continue its own Safe Boot mode. If Safe Boot fails to resolve your problem, or if your storage is malfunctioning, or the OS is damaged beyond repair, you have to erase storage and reinstall the operating system, which is why backup is such an important administrative safety net.

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