Those features are:. This feature prevents anyone who does not know the firmware password from starting the Mac up from a disk other than your designated startup disk. Secure boot makes sure that the Mac is only able to boot from a legitimate, trusted Mac operating system or Microsoft Windows operating system under Boot Camp.
What does it mean when your Mac says the disk is full?
By default, the T2 chip disallows booting from any external media. This can be changed in the Startup Security Utility. To do this:. Startup Security Utility, available on new Macs with the T2 chip. You can set a firmware password to keep anyone without that password from starting up from a disk other than your designated startup disk. As the Mac starts up, it verifies the integrity of the operating system on the startup disk to ensure that it is legitimate.
If the OS is either unknown or not verified as legitimate, the Mac connects to Apple to download the information it needs to verify the OS. That information is unique to each Mac and is used to make sure that the Mac is starting up from an OS that is trusted by Apple.
An internet connection is required for verification of an unknown or non-legitimate operating system, so make sure that the Mac is connected to a Wi-Fi network or Ethernet. Clicking Update opens the macOS installer, which can then be used to reinstall macOS on the startup disk.
The other option is to click Startup Disk and select a different startup disk, which the Mac then attempts to verify. When your Mac starts up with Medium Security enabled, it only checks whether or not the operating system has been properly signed by Apple or Microsoft. No internet connection is required unless Secure Boot determines that the operating system must be updated before it allows the system to boot.
This means that any compatible version of macOS or Windows can be used to boot the Mac, or even Linux distributions that are designed for installation on Macs. A startup drive that is experiencing problems is likely to prevent your Mac from starting, so you may find yourself in a catch The easiest solution by far is to boot from a different device. To boot from another hard drive or a USB flash device, hold down the option key and start up your Mac.
The Mac OS startup manager will appear, allowing you to select the device to boot from. To start up in Safe Mode , hold down the shift key and then start your Mac.
- Use Startup Disk preferences?
- How to Clean Your Almost-Full Startup Disk on MacBook Air/Pro!
- How to Clean Up Startup Disk on MacBook Air/Pro with MacClean.
It will also delete some of the startup caches that may also be preventing your Mac from starting successfully. When First Aid is finished, restart your Mac normally. You should use this startup mode only for troubleshooting and not for running day-to-day applications. Press return or enter after you type the above line. Do you have a thumb drive to install macOS Sierra to?
You might try removing the disk and using an enclosure or USB reader to mount the disk on a different Mac. In the end, it's probably easier to salvage what stuff you know you need, nuke the disk, and make a clean installation. After your able to mount the disk erasing the files the other website recommended.
Hope this helps and good luck on recovery your data. Matthew N Matthew N 2 2 gold badges 7 7 silver badges 25 25 bronze badges.
How to use macOS Recovery to restore the operating system on your Mac
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Why Is My Startup Disk Full? Powerful Tips to Free Up Space on your Mac - Parallels Blog
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