disk utility first aid is stuck won't quit

You can Force Quit:

1. Press COMMAND-OPTION-ESC to open the task manager. Select Disk Utility from the list of running tasks then click on the Force Quit button.
2. CTRL- or RIGHT-click on the Disk Utility icon on the Dock. Select Force Quit from the context menu.
3. Open Activity Monitor. Under the Name list, locate and select Disk Utility. Click on the Quit button in the upper left corner, then click on the Force Quit button.

Open a terminal window. Run ps -ef | grep fsck . You'll see the a process named fsck_hfs running. This is the file system checker for the hfs file system. Rerun this periodically and you'll see that the elapsed CPU time has increased. In my experience, if this is increasing, the process is running and is making progress, as opposed to being hung. I wouldn't worry or think about forcing a quit until this number stalls. Patience.

Do you know if force quitting while Disk Utility first aid is "checking" a Time Machine disc will cause me to lose data?

Thanks

First Aid seems to be slowed down significantly by the accumulation of all of the local snapshots that Time Machine copies to the backup drive. Even running First Aid on my iMac's boot drive (an SSD) is much slower after upgrading to High Sierra. Clicking on Show Details will confirm checking these snapshots takes time. Apple really ought to address this matter.

Apple doesn’t routinely monitor the discussions. These are mostly user to user discussions.

Send Apple feedback. They won't answer, but at least will know there is a problem or a suggestion for change. If enough people send feedback, it may get the problem/suggested change solved sooner.

Click here to send Feedback

It will not cause data loss assuming all you did was run First Aid.

I find that trying to run FirstAid on a Time Machine drive takes forever and often fails after hours of checking.

Trying to run FirstAid on a Time Machine volume takes F O R E V E R.

Kappy has explained how to force quit the process.

Check you log file, it may have completed. (command-L)

Oops, log file no longer exists. You probably have no option except a force quit.

Thanks Kappy. I figured as much but wasn't sure, I quit out with no problems.