READ. USE AT YOUR OWN R I S K - I’m not responsible for your machine- If your cheap and want me to fix it for you and it breaks thats your problem not mine, take it to an apple store if you want professional help. This works in most cases- READ BELOW for other fixes.
Repair error on startup volume on Mac disk utility with one simple trick.

1.Restart computer
2 Hold Command and S key
3. login
4. type fsck -fy hit enter
5.type reboot

or try the following then do the above:

Fix #2 Mac Stuck on White Screen?
Disconnect all peripherals
Restart in Safe Mode
Run Disk Utility
Reset NVRAM (or PRAM)
Power up your Mac with the Startup Manager and select your Startup Disk Manually
Launch Single User or Verbose Mode with Terminal
Reinstall macOS or OS X
Run Apple Diagnostics or Apple Hardware Test

Fix #3
Try pressing shift-option-command and pressing the power button for 5 seconds when its off-make sure the power adapter is attached when you do it the orange with turn to green after you let go then return to orange its resetting the EFI

Try :try holding Command R at boot then run disk utility

Great Resources for More Terminal commands
[ Ссылка ]

#diskutility #imac #macbook

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