How to Open a DMG File

What is a DMG file?

DMG (Apple Disk Image) is Apple's UDIF (Universal Disk Image Format) container — effectively a virtual disk in a single file, and the standard way Mac apps and installers are distributed. When you double-click one on a Mac, it "mounts" exactly like a physical external drive would, complete with its own filesystem (almost always HFS+ or APFS) and icon on the desktop.

Structurally, every modern DMG ends with a fixed 512-byte block called the "koly" trailer, which records the image's true uncompressed size, checksum information, and the location of an embedded Apple XML property list (plist). That plist lists every partition in the disk image by name, along with a compact binary table describing how each partition's data is encoded — stored raw, or compressed with zlib, bzip2, Apple Data Compression, or the newer LZFSE. That's exactly the structure this page's tool reads directly, without needing to actually mount or decode the filesystem inside.

How to open a DMG file on Mac

1. Double-click the .dmg file — it mounts automatically and usually opens a Finder window showing its contents.
2. Drag the app (or other contents) to wherever you want it, most commonly the Applications folder.
3. When finished, "eject" the mounted disk image from the Finder sidebar or desktop — the original .dmg file can then be deleted safely, since its contents have already been copied out.

Installing an app from a DMG (drag to Applications)

Most Mac app downloads are a DMG whose window shows the app's icon next to a shortcut to your Applications folder, often with an arrow between them. That layout is the installer: there's nothing to "run".

1. Double-click the .dmg in Downloads to mount it.
2. Drag the app icon onto the Applications shortcut in the same window. If there's no shortcut, drag it onto Applications in the Finder sidebar.
3. If the window contains a .pkg file instead of an app, double-click the .pkg and follow the installer's steps.
4. Eject the disk image (eject icon in the Finder sidebar), then move the .dmg file to the Trash — the app now lives in Applications and doesn't need it.
5. Open the app from Launchpad or the Applications folder. The first launch may show a security prompt (see the next section).

"App can't be opened", "Apple could not verify" or "is damaged"

These messages come from Gatekeeper, macOS's check that downloaded apps are signed by a registered developer and notarized by Apple. They appear when you open the app, not the DMG itself. Only bypass them for software you trust from the developer's own website.

"Apple could not verify ... is free of malware" (macOS Sequoia and later)

On macOS Sequoia (15) and later, the old shortcut of Control-clicking an app and choosing Open no longer bypasses this warning. Instead:

1. Try to open the app once and click Done on the warning.
2. Open System Settings > Privacy & Security and scroll down to the Security section.
3. Next to the message saying the app was blocked, click Open Anyway, then confirm with your password or Touch ID.
4. The app opens, and macOS remembers your choice for that app.

"can't be opened because Apple cannot check it for malicious software" (older macOS)

On macOS Sonoma and earlier, Control-click (or right-click) the app in Applications, choose Open, then click Open in the dialog. The same System Settings > Privacy & Security > Open Anyway route also works.

"... is damaged and can't be opened. You should move it to the Trash."

First re-download the DMG — a truncated download really can damage the app. If a fresh copy from the official site still shows this, the usual cause is an app that isn't notarized combined with the quarantine flag macOS adds to downloads. If (and only if) you trust the developer, you can remove that flag in Terminal:

xattr -dr com.apple.quarantine "/Applications/Example.app"

Replace the path with your app's. This turns off Gatekeeper's check for that one app, so never do it for software from an unofficial source.

How to open a DMG file on Windows

1. Install 7-Zip (free) and right-click the .dmg file, choosing 7-Zip > Open archive or Extract files.
2. This works for many DMG images, especially simpler, uncompressed or zlib-compressed ones, but can fail on images using newer compression (like LZFSE) or unusual partition layouts.
3. If 7-Zip fails, a dedicated third-party DMG-extraction tool for Windows may handle it — or, if you have access to a Mac (including a cloud/virtual one), extracting there and transferring the files is the most reliable fallback.
4. Use the tool on this page first to see the compression method and partition layout — this tells you upfront whether a simple tool like 7-Zip is likely to work.

How to open a DMG file on Linux

1. Install dmg2img (available in most distributions' package managers) and run dmg2img yourfile.dmg to convert it into a raw disk image.
2. Mount the resulting image with an HFS+ or APFS driver — hfsprogs or hfsplus packages provide HFS+ support; APFS support on Linux is newer and less universally packaged.
3. 7-Zip (via p7zip) can also be tried directly on simpler images, the same as on Windows.

Can you open a DMG on iPhone, iPad, Android or Chromebook?

Not in any useful way. A DMG almost always contains a macOS app, and macOS apps can't run on iOS, iPadOS, Android or ChromeOS — even on iPads with the same Apple silicon chips. The Files app on iPhone and iPad doesn't mount disk images. If you need the app on a phone or tablet, look for the developer's App Store or Google Play version instead. If the DMG holds documents rather than an app, open it on a Mac (or with 7-Zip on Windows), copy the files out and transfer them.

Convert a DMG to ISO (or a writable image)

On a Mac, the built-in hdiutil command converts between image formats. To turn a DMG into an ISO-style image:

Keep in mind that converting the container doesn't change the filesystem inside: the result is still HFS+ or APFS, so Windows still can't read it, and it won't magically make a Mac app run on a PC. ISO conversion is mainly useful for virtual machine software or burning tools that only accept .iso. Two other handy conversions:

• Writable copy: hdiutil convert Example.dmg -format UDRW -o Example-rw creates a read/write DMG you can mount and edit.
• Smaller compressed copy: -format ULFO (LZFSE, macOS 10.11 and later) or -format UDZO (zlib, readable by older tools such as 7-Zip) re-compresses it.

On Linux, dmg2img Example.dmg Example.img produces a raw image, as described above.

Common DMG file problems and how to fix them

"This disk image is corrupted and cannot be opened" (on Mac)

Usually means the download was incomplete or interrupted. Re-download the file, and verify its size matches what the source lists, if given.

7-Zip can't extract the file on Windows

Some DMG images use compression methods or partition layouts 7-Zip doesn't fully support. Check the tool on this page first — if it shows LZFSE compression or several partitions, that's a common cause of 7-Zip failures, and a Mac (or a dedicated Windows DMG tool) will be more reliable.

The disk image won't eject ("Resource busy" or "one or more programs may be using it")

Something still has a file open on the mounted image — most often the app itself, launched directly from the DMG, or a Finder or Quick Look window. Quit the app, close Finder windows showing the image and try again. If it still refuses, run hdiutil detach "/Volumes/Example" in Terminal (use the volume name shown in Finder), and add -force as a last resort. Restarting the Mac always unmounts it.

"hdiutil: attach failed - no mountable file systems"

The image opened but macOS found no filesystem it can read. Usually the download is incomplete (re-download it and compare the size with the source); occasionally the DMG contains an APFS volume and you're on a very old macOS that predates APFS (before High Sierra).

The mounted disk image is read-only and won't let me save changes

Most distributed DMGs are intentionally read-only. If you need a writable copy, use Disk Utility's Images > Convert option on a Mac to create a read-write version.

Related file extensions

Technical references

Apple has never published an official DMG specification. The most complete public technical reference comes from the libyal forensics project, whose reverse-engineered documentation is widely relied on by disk-image tooling.

• Mac OS disk image types — libmodi documentation (libyal project) — A detailed, community-maintained reverse-engineered reference for Apple's disk image formats, used by forensic and archival tools.

Frequently asked questions