Unable to run first aid in recovery mode

If Disk Utility reports that the disk appears to be OK or has been repaired, you’re done. You can click Show Details to see more information about the repairs. Otherwise, you may need to do one of the following.

• If Disk Utility reports “overlapped extent allocation” errors, two or more files occupy the same space on your disk, and at least one of them is likely to be corrupted. You need to check each file in the list of affected files. Most of the files in the list have aliases in a DamagedFiles folder at the top level of your disk.
  • If you can replace a file or re-create it, delete it.
  • If it contains information you need, open it and examine its data to make sure it hasn’t been corrupted.
• If Disk Utility can’t repair your disk or it reports “The underlying task reported failure,” try to repair the disk or partition again. If that doesn’t work, back up as much of your data as possible, reformat the disk, reinstall macOS, then restore your backed-up data.

An article : Disk Utility for Mac: Repair a disk using Disk Utility

I'm just going to assume that you're trying to run First Aid on the startup disk and not some other drive, right?

First Aid is part of the Mac OS, so the report that it can't even be run in recovery mode suggests that one of two things is true: either the Mac OS is corrupted and needs to be reinstalled (you can do that from Disk Utility) OR the hard drive is actually damaged.

The SSD may have failed. Try erasing it then reinstalling OS X. If that doesn't work then the SSD is probably gone.

Install El Capitan from Scratch

Backup if possible before continuing.

1. Restart the computer. Immediately after the chime hold down the Command and Rkeys until the Apple logo appears. When the Utility Menu appears:
2. Select Disk Utility from the Utility Menu and click on Continue button.
3. When Disk Utility loads select the volume (indented entry, usually Macintosh HD) from the Device list.
4. Click on the Erase icon in Disk Utility's main window. A panel will drop down.
5. Set the Format type to Mac OS Extended (Journaled.)
6. Click on the Apply button, then wait for the Done button to activate and click on it.
7. Quit Disk Utility and return to the Utility Menu.
8. Select Reinstall OS X and click on the Continue button.

What if you dont have a copy of osx to re-install with?

Alex360noscope: you can start up the computer with the COMMAND + OPTION + R keys to invoke the online version of the recovery and reinstall the OS from an online copy.

Had the same problem (I would even guess that this is a bug in Sierra recovery).

I could solve it by running diskutil from command line (in recovery mode), similar as described here: https://computers.tutsplus.com/tutorials/how-to-verify-and-repair-a-disk-from-th e-os-x-command-line--cms-21561

I did "diskutil verifyDisk /dev/disk0" and then "diskutil repairDisk /dev/disk0" which fixed the errors (and afterwards "diskutil verifyVolume disk18", but there was no error found).

You should however be careful with diskutil from command line (and have a backup first).

Afterwards I ran the graphical Disk Utility again (still in recovery mode) to be on the safe side. It did not bring up the problematic prompt anymore and it even fixed something additional on my partition successfully. So I would recommend to do that, too.

Thanks jakob.j.w, I applied your command line with success.

- You choose the boot by pressing "option key" when starting your computer.

- You choose "Recovery Boot",

- After choose Terminal and write the command line:

"diskutil verifyDisk /dev/disk0"

and after the verification:

"diskutil repairDisk /dev/disk0"

For me it solved:

"Problems were found with the partition map with might prevent booting"

"Error: -69766: The partition map needs to be repaired because there's a problem with the EFI system partition's file system"

Before repairing, the system tell you :

"Repairing the partition map might erase disk0s1..."

A clone, a Time Machine disk is a good idea .

There is not a lot of choices, it works or you have to re-install your OS, in my case macOS Sierra 10.12.2 (16C67).

DiskUtility confirmed after that everything was back to normal.

(First, I tried to boot with a USB key and use DiskUtility, it's not working. Use directly the Recovery.)

Thanks again Jakob.

Mac OS is completely free to reinstall. Unlike windows, you don't need a registration key to reinstall, so your good :D