When macOS says the app is damaged

MacOS has a sentence it likes to produce when it is unsure of a file: the application is damaged, and should be moved to the bin. Most of the time, in this studio, the file is not damaged. It is quarantined. The system saw it arrive from a browser, or from a mail attachment, and it would like a human to hesitate. I respect the instinct. I do not enjoy performing the same explanation in the hallway, so it lives here.

What the warning actually means

A disk image can be corrupted. That happens, and it looks similar, which is why the warning is not a joke. More often, on the machines I set up, the bytes are fine and a flag is set on the application bundle. The flag is called quarantine. Gatekeeper reads it and refuses to open the app, then phrases the refusal as damage, which sends people back to the download button. A second download, with the same flag, fails in the same way. I have watched a colleague do this three times and begin to distrust the developer, the mirror, and me, in that order.

Before you touch a command, check the obvious. Did the disk image open? Did the application copy all the way into the Applications folder, or is it running from the image? Eject the image. Open the copy that lives in Applications. If the warning repeats, you are probably looking at quarantine, not at a ruined file.

The quarantine flag

The flag is metadata. It does not change the picture, the audio, or the code you meant to run. It records where the file came from. That record is useful when a program arrived from a place you do not recognise. It is less useful when you fetched a build you were already expecting, from a page you were already reading, and the only thing standing between you and the work is a sentence about damage.

I still read the sentence. I look at the domain I downloaded from. I look at the size, because a four-megabyte “suite” is a different kind of problem. Then, if I trust the source, I clear the flag. I do not clear it for a file a stranger sent to the studio address with a cheerful subject line. That file can wait until morning, and morning can include not opening it.

The command I keep

I keep one command, and I paste it rather than retype it, because a mistyped path is how you “fix” the wrong bundle. Replace the name with the application you actually have.

xattr -d com.apple.quarantine /Applications/Compresto.app

Run it in Terminal, from an account that is allowed to write to Applications. If the system asks you to confirm, confirm only after you have read the path. Then open the application from the folder, not from the disk image you have already ejected. The first launch may still ask you to approve the developer under Privacy & Security. That second dialog is a different door. Approve it if you meant to install the program. Do not approve it because a dialog is in your way and the kettle has boiled.

If the command replies that the attribute is not found, the flag was never there. In that case the file may actually be damaged, or it may be the wrong architecture: an Intel build opened on Apple silicon without the translation you expected, or the reverse. Download the build that matches the chip. The catalogue lists them separately when I know them to be separate. Take the matching one, even if it sits lower on the page.

When I do not bypass it

I do not clear quarantine on a machine that is not mine. A client’s laptop is not the place for my habits, and a borrowed machine in a colour house is not the place either. I send files, not installers, unless someone has asked in words for the installer.

I do not clear it when the download came from a link I was not looking for: a comment under a video, a shortened address, a mirror whose name is almost the developer’s name. Almost is the whole trick. I would rather wait a day and fetch the build from the page I already trust.

I do not run a broader command that strips every attribute from every application in the folder, even though I have seen it recommended in a forum voice that sounded sure of itself. Sure is cheap. A wide command will also remove notes I meant to keep, and it will teach the next person that Terminal is a place where you paste mysteries. We do not do that at this table.

After it opens

Once the application opens, leave it in Applications and throw the disk image away, or file the image with the version number if you are the sort of person who needs last month’s build. I am that sort of person for a few programs, and a hoarder for none of the others. A folder called installers is allowed. A desktop covered in disk images is how the wrong build gets dragged across in June.

If a program asks for a helper, a login item, or a permission to record the screen, read the request against the job you actually wanted. A compression tool does not need your camera. A menu utility may need permission to draw over other windows, and that one I will grant, because otherwise it cannot do the only thing it is for. The difference is not subtle if you are willing to read the sentence.

When the warning was right — when the file really was damaged — delete the copy and download it again from the same place, once. Compare the size to the size written on the catalogue page. If they disagree by more than a rounding error, stop. Write to me, or write to the developer, and do not keep trying mirrors until one of them is polite enough to open. Polite malware opens.