First Aid is a feature of Disk Utility, a native app that can be found in the Utilities folder. It is used for checking out the hard drive’s health and its reparation in case it did not suffer serious corruption. The tool is used when a computer shows red flags such as crashing, cryptic error messages, etc., and with the goals of preventive maintenance. Some users get warning messages after running First Aid. They may also experience kernel panics, have problems with Finder freezing and loose files from the cloud storage (for example, Dropbox).
If you have the same issue, try the next steps.
- Go to the System Preferences → Security & Privacy, then choose FileVault.
- Click the lock icon to unlock it. Then the system will ask you to type your administrator name and password.
- Click Turn Off FileVault and Turn Off Encryption.
Note: After you turn FileVault off, files on a computer are starting to decrypt. This process takes some time depending on the data volume. Meanwhile, you can still use a Mac for other unrelated tasks.
Reinstalling High Sierra Using Recovery Mode
- Make sure you have an Internet
- Turn your Mac off and wait for about half a minute.
- Press the power button and hold both the Command and R keys until you hear the chime noise.
- Download new OS X to reinstall it on your computer. Remember to have your Apple ID and password.
- Click Install Mac OS X and follow instructions displayed on the screen.
Note: Before reinstalling the system make sure that you have your data backed up. You can then restore it using the Migration Assistant.
If the issue persists, the following approach may be applied.
Reinstalling High Sierra after Erasing a Hard Drive
- Turn on your iMac Pro and launch the Disk Utility. For this, click on the Finder Icon and choose Applications. Scroll to the bottom of the window and click on Utilities → Disk Utility. Click Continue.
- Select your hard drive in the sidebar of Disk Utility.
- Click the Erase button after filling in the Name, Format and Scheme fields.
- Then quit Disk Utility to return to the Utilities.
- Install High Sierra again. Open Disk Utility First Aid and check with it if there are no problems with the hard drive.
Then you can make sure that FileVault does not cause problems by enabling it. Go to the System Preferences, choose Security & Privacy tab. Click the Lock icon to make changes. Then turn FileVault on.
If you do not get any crypto_val warnings, move further with restarting your iMac in Safe Mode. Erase the hard drive again and run First Aid. Enable FileVault again and test the disk with First Aid.
Note: Erasing a disk permanently removes all the data on it. Copy files you would like to save to another disk before proceeding.