On Yosemite 10.10 Onyx returns the following error:
Error: -69845: File system verify or repair failed Underlying error:
8: POSIX reports: Exec format error
The disk needs to be repaired.
I tried repairing the disk in recovery mode but the disk utility returns a message that everything is fine, however, the after running Onyx the second time the error persists.
On a related matter, the option to repair permissions is not available in the Disk Utility.
Best Answer
I had the same issue. I was able to fix it in an interesting way.
I have been testing El Capitan on an external drive. So, I thought, why not try Disk Utility using OS 10.11.x and (after the second pass) it repaired the drive. As the Beta was on a separate disk, and the Macintosh HD was unmounted at the time, it was analyzed and repaired. Just like using a 3rd party app.
At least this was a "free" way to fix it. Saved the hassle of reformatting and restoring.