Aspecten Mac software, aspect by aspect
Log in

Help

Fixing “app is damaged and can’t be opened”

macOS has one warning that still sends people to a search box, even in 2026. The window says the application is damaged and cannot be opened, and it offers Move to Bin. In most of the cases that land in my mail, the file is not damaged. Gatekeeper has decided it does not like the signature, or the quarantine flag on a download has not been cleared.

What the sentence actually means

Three different situations share that wording:

  1. The copy is incomplete — a disk image that stopped at 80%, a ZIP that failed over SMB.
  2. The copy is complete, but it was not signed (or was signed with a certificate Apple no longer accepts).
  3. The copy is signed, but the quarantine attribute from Safari or a mirror is still attached, and the check failed once.

Only the first one is actual damage. You can tell: the file size will not match the listing, or the image will not mount. Throw it away and fetch it again. Do not “repair” a half-file.

The other two are policy. Apple would like software to come from the App Store or from a Developer ID with notarisation. Plenty of useful Mac tools still do not. Aspecten notes that fact on the sheet; this page is only the mechanics of launching them on a machine you control.

Right-click Open

For case 2 and most of case 3, this is still the whole procedure:

  1. Make sure the app is in /Applications, not on the desktop, not inside the disk image.
  2. In Finder, right-click (or Control-click) the app.
  3. Choose Open, not the ordinary double-click.
  4. In the dialogue, confirm Open.

After that, ordinary double-clicks work. You are not turning off Gatekeeper for the system. You are making an exception for one bundle. I do this on the Intel mini every time I test a build that has not been notarised.

When that is not enough

If right-click Open still fails, the quarantine flag may be stuck. In Terminal:

xattr -cr /Applications/Compresto.app

Replace the name. Then try right-click Open again. -c clears extended attributes; it is blunt. Do not run it on your whole disk. Do not run it on an app you have not decided to trust.

System Settings → Privacy & Security sometimes shows an Open Anyway button at the bottom, after a failed launch. That is the same exception as right-click Open, in a different room. I prefer Finder; I can see which icon I am clicking.

If the warning persists after a clear download, a right-click, and xattr, treat it as case 1 and fetch a new copy. I have twice had a “direct” mirror serve an HTML error page saved with a .dmg extension. Disk Utility will not be kind about that, and nor should it.

How I update a programme

I do not let random apps update themselves in the background if I am in the middle of a test. The sequence I use:

  1. Quit the programme. Check Activity Monitor if it has a helper; quit that too.
  2. Move the old .app to a folder named Expired on an external disk, not to the Bin, until the new build has launched once.
  3. Install the new build into Applications.
  4. Launch, confirm the version in the About window, then throw the expired copy away.

Sparkle-based updaters (the ones with a “Check for Updates…” menu item) are fine for software I already trust. I still read the release note. A jump from 5.2 to 6.0 is not the same as 5.2.3 to 5.2.4.

For Mac App Store titles, the Store is the updater. Fighting it with a copied .app from elsewhere is how people end up with two icons and a preference pane that writes to the wrong container. I do not mix those sources.

What this is not

This is not a guide to disabling Gatekeeper, SIP, or FileVault. I will not publish those steps. If a programme needs them off in order to launch, I will say so on its sheet and I will not recommend it for a work machine.

It is also not a promise that every file linked from a programme page is notarised. Read the compatibility line. If you are not willing to make a per-app exception, stay with App Store builds.