This covers the start up mode using Command + R keys.
Note: Recovery Mode takes longer to boot - this is normal.
Things you can do in Recovery Mode:
- Restore from Time Machine back up
- Reinstall the last macOS that was previously installed
- Go to Apple Support help online
- Use Disk Utility to partition, repair, erase, format drives
- Add or remove an EFI password (must know password if removing)
- Troubleshoot network connection
- Open Terminal from Recovery Partition (reset user password, disable/enable SIP, change date, etc.)
- Select a different startup disk
- See the Installer Log
If you cannot startup in Recovery Mode by this startup combination, the recovery partition may be corrupt or non-existent, keyboard may be faulty, or the Mac was running an older OS (10.6 or older). Try a wired keyboard, Internet Recovery, a different startup disk, or bootable installer.
Using Recovery environment to backup folders and data
In some cases (for example, you replaced PCH on 16" Macbook Pro and it wont boot untill DFU Restore clears the ME region, target disk mode dows not work too) you can only use recovery mode.
You can actually backup any folder or even whole partition using Disk utility. Simply mount target drive and unlock source drive, then create an image of folder you need.