everyday mac tools

Can you delete DMG files after installing an app on a Mac?

· 6 min read

Yes. A DMG is only the box the app was delivered in. Once the app has been copied into your Applications folder and opens from there, the DMG in Downloads has done its job and can go in the Trash, along with any PKG installer you have already run. The one thing to check first is that the app really was copied, because it is easy to run an app straight from the disk image for months without noticing.

What a DMG file actually is

A .dmg file is a disk image: a single file that macOS can mount as if it were a drive. Double-click one and two things happen. A new item appears in the Finder sidebar under Locations, and a window opens showing what is inside, which for most apps is the app icon and a shortcut to the Applications folder with an arrow between them.

That window is an invitation, not an installation. Nothing is installed until you drag the app onto the Applications shortcut, which copies it onto your Mac. After that there are three separate things:

  1. The app in Applications, which is the one you keep.
  2. The mounted disk image in the sidebar, which you eject.
  3. The .dmg file in Downloads, which you can delete.

Deleting the DMG does not uninstall the app, and keeping it does not make the app work any better. Some disk images hold a .pkg installer instead of an app. In that case you run the installer, it puts the files where they belong, and both the PKG and the DMG are finished with.

Check the app is really installed

Do this before deleting anything, especially for apps you installed in a hurry.

  1. In the Finder sidebar, click the eject button next to any disk image still listed under Locations. If Finder says the disk is in use, an app is running from it, and that is your answer already.
  2. Press Shift-Command-A in Finder to open Applications and look for the app.
  3. Quit the app and open it again from Applications, Launchpad or Spotlight.

For an app that is open right now, there is a quicker check. Right-click its icon in the Dock, choose Options, then Show in Finder. If Finder shows the app inside Applications, it is installed. If it shows the app inside a volume named after the download, you have been running it from the disk image.

That matters for more than tidiness. A downloaded disk image is usually read-only, so an app running from one often cannot update itself, and it vanishes the moment the image is ejected or the DMG is deleted. The fix takes seconds: quit the app, drag it from the image window into Applications, eject the image, and open the copy in Applications from now on. If you kept it in the Dock, remove the old icon and add the new one, since the old Dock entry points at the disk image.

Find every DMG and PKG you have collected

Most of them sit in Downloads, often in several copies, because a browser gives each repeat download a new name with a number added.

In Finder, open Downloads, choose View, as List, then click the Kind column header. Disk images are listed as Disk Image and installers as Installer package or Installer flat package, so they group together. Click the Size column afterwards to see which are worth the effort. Tidy the Downloads folder without losing anything covers the rest of that folder.

To look further than Downloads, Terminal can list every DMG and PKG in your home folder with its size:

find ~ \( -name "*.dmg" -o -name "*.pkg" \) -not -path "*/Library/*" -exec du -h {} + 2>/dev/null

The -not -path part skips the Library folder, where apps keep their own files and where deleting things by hand is a bad idea. Read the list, then delete from Finder rather than from Terminal, so everything passes through the Trash first and can be put back if you change your mind.

When you have finished, empty the Trash. Until then the space is not returned. You emptied the Trash but your Mac got no space back explains the cases where even that is not enough.

The installers worth keeping

A few installers deserve a place somewhere other than Downloads:

  • Apps you cannot download again. Older versions, discontinued apps, or software from a developer whose site has gone. If a license is tied to a particular version, keep the matching installer with the license email.
  • Installers for offline machines. A Mac that is rarely online is easier to set up from a folder of installers.
  • Drivers for older hardware. Printer, scanner and audio interface drivers can disappear from a maker’s site when a model is retired.

Move these to a folder called Installers on an external drive or in your archive, and delete the rest. Anything you can download again from the developer or the App Store is not worth the space.

PKG receipts and old macOS installers

Once a PKG has run, macOS keeps a receipt of what it installed. Receipts are not the installer and take almost no space, so leave them alone. They are useful, too: pkgutil --pkgs lists every package installed on the Mac, and pkgutil --files followed by a package name lists the files it put in place, which helps when you later want to remove something completely. Uninstall an app on a Mac completely covers that job.

The biggest single installer on many Macs is not in Downloads at all. An app called Install macOS followed by a version name can sit in Applications long after the update it was downloaded for. Not enough space to update macOS explains when it is safe to delete.

Doing it in one pass

The manual route works well enough for one folder. If installers are scattered around, or you have downloaded the same one four times, Crumb can take some of the legwork out of it. Its Organize tool tidies a messy folder such as Downloads by type, so disk images and installers end up together, and Duplicates finds the repeated copies. If you are unsure what a particular file is, Ask Crumb explains what the item is, whether it comes back on its own, and what breaks if it goes, then proposes a plan. Nothing is deleted until you approve it.

Crumb’s whole-Mac audit and one full cleanup are free. Organize, Duplicates and Ask Crumb are part of the $9 one-time unlock, on up to two Macs.

Questions

Will deleting a DMG uninstall the app? No. The app in Applications is a separate copy. Deleting the DMG only removes the box it came in.

Finder will not let me eject the disk image. Why? Something is running from it, almost always the app itself. Quit it, then eject. If it still refuses, use the Dock check above to find which app is holding it open.

Is it safe to delete a PKG file after installing? Yes. The installer has already copied its files into place, and deleting the PKG does not remove what it installed.

Do DMG files slow a Mac down? No. They only take up disk space. A Mac that is short of free space can slow down, which is the real reason to clear them out.