hdiutil: image not recognized / no mountable file systems macOS Origin: Platform & cloud OSI layer 7 · Application Last updated 5 Nov 2026

macOS: hdiutil: attach failed - image not recognized / no mountable file systems

The .dmg file is corrupted, incomplete, or not actually a disk image (often an HTML download page).

Exact message you may see hdiutil: attach failed - image not recognizedhdiutil: attach failed - no mountable file systemsno mountable file systems dmgThe disk image couldn't be opened. image not recognizeddmg is corrupted and can't be opened
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Seen on: macOS

Meaning

Check size and type: file app.dmg. A tiny file or "HTML document" means the download failed (blocked, login page). Re-download, verify checksum, and try hdiutil verify. Encrypted or unusual formats need the right tool/password.

Common causes

  • Interrupted/incomplete download
  • Server returned HTML error page named .dmg
  • Corrupted file after transfer
  • Wrong file type (zip/pkg renamed)
  • Unsupported/encrypted image

⚡ Quick fix

  1. file app.dmg and compare size
  2. Re-download over a stable connection
  3. hdiutil verify app.dmg

Detailed fix by platform

macOS

  1. file app.dmg && shasum -a 256 app.dmg && hdiutil verify app.dmg

How to diagnose

  1. Type — file says disk image?
  2. Size — Expected?
  3. Checksum — Match?

🔧 Still not fixed?

Many errors look alike. If the steps above didn’t solve it, one of these is probably what you’re facing:

Where this error sits

Origin: Platform & cloud. Errors that are often confused with or caused by this one (click to open):

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