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Bad Block Scan from Terminal

How to do a bad block scan of a volume.

This reads the whole disk and reports any (hardware) errors found.

List available disks: diskutil list
Find the ID of volume to be scanned in the list, eg /dev/disk2

Enter this: sudo fsck_hfs -dylS DISKID
Example: sudo fsck_hfs -dylS /dev/disk2s2

Meaning of options...
d = output debugging info
y = assume a yes response to all questions
l = live fsck (lock down and test-only)
S = Scan disk for bad blocks





I usually write a blog post about once a week. The latest post can be viewed here: Think for Yourself: In the end, everything is just an opinion. Be skeptical, and think for yourself! (posted 2026-04-25 at 21:12:02). Or go to the Home Page of My Blog to choose a post to view.

I do podcasts too! You can listen to my latest podcast, here: OJB's Podcast 2026-04-14 How Far is that Star?: How would we really know how big the universe is? Or subscribe to my podcast RSS feed, on my RSS Feeds page.

If you're not sure what to view from the thousands of pages on my site, here are some suggestions: My Latest Airshow Report (photos and movies from Warbirds Over Wanaka, 2026), My Favourite Wines and Beers (tasting notes for some of my favourites), An Interesting Astronomical Observation (learn a bit about astronomy from these observing notes), See Some Photos (A short rail journey through the Taieri Gorge), Read Some Mac Tips (Learn about how to use your Mac, and fix some problems).


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