Safari can’t open the file “.dmg” because no available application can open it

Question

macOS Monterey 12.5, MacBook Air, M1, 2020

I am pretty sure I was learning how to partition my disk to install Linux and I may have done something with diskutil like unmounting my primary disk. I have no idea if that was correct or not. I was exploring, following some advice, and trying to understand what was happening by trying out some commands.

Everything about my computer appears to be fine except I seem to not be able to install any new applications. Anything I install from homebrew gives an error message that the installation is corrupted when I try to launch it. When I download a .dmg file in the browser and double click on it, I get "No available application can open it".

I was told (not sure if this is correct) that if your disk is unmounted you can still access files but you cannot install software, for some reason. So I just thought I needed to remount a disk or something.

I did diskutil list:

/dev/disk0 (internal):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      GUID_partition_scheme                         251.0 GB   disk0
   1:             Apple_APFS_ISC ⁨⁩                        524.3 MB   disk0s1
   2:                 Apple_APFS ⁨Container disk3⁩         245.1 GB   disk0s2
   3:        Apple_APFS_Recovery ⁨⁩                        5.4 GB     disk0s3

/dev/disk3 (synthesized):
   #:                       TYPE NAME                    SIZE       IDENTIFIER
   0:      APFS Container Scheme -                      +245.1 GB   disk3
                                 Physical Store disk0s2
   1:                APFS Volume ⁨Macintosh HD⁩            23.4 GB    disk3s1
   2:              APFS Snapshot ⁨com.apple.os.update-...⁩ 23.4 GB    disk3s1s1
   3:                APFS Volume ⁨Preboot⁩                 847.4 MB   disk3s2
   4:                APFS Volume ⁨Recovery⁩                1.7 GB     disk3s3
   5:                APFS Volume ⁨Data⁩                    135.6 GB   disk3s5
   6:                APFS Volume ⁨VM⁩                      6.4 GB     disk3s6
   7:                APFS Volume ⁨Nix Store⁩               2.4 GB     disk3s7

It seems like Disk 3 is the main disk, then someone said I should see which apfs volume is the mount point:

0: diskutil apfs list
APFS Containers (4 found)
|
+-- Container disk3 641E9C2B-3A65-49CA-89DF-5602B982CC6E
|   ====================================================
|   APFS Container Reference:     disk3
|   Size (Capacity Ceiling):      245107195904 B (245.1 GB)
|   Capacity In Use By Volumes:   171067355136 B (171.1 GB) (69.8% used)
|   Capacity Not Allocated:       74039840768 B (74.0 GB) (30.2% free)
|   |
|   +-< Physical Store disk0s2 74B7C79D-2DFC-4F34-B96D-E6DE7CB8A2E8
|   |   -----------------------------------------------------------
|   |   APFS Physical Store Disk:   disk0s2
|   |   Size:                       245107195904 B (245.1 GB)
|   |
|   +-> Volume disk3s1 38D89153-A250-4536-8442-126F420B8F8D
|   |   ---------------------------------------------------
|   |   APFS Volume Disk (Role):   disk3s1 (System)
|   |   Name:                      Macintosh HD (Case-insensitive)
|   |   Mount Point:               /System/Volumes/Update/mnt1
|   |   Capacity Consumed:         23363510272 B (23.4 GB)
|   |   Sealed:                    Broken
|   |   FileVault:                 Yes (Unlocked)
|   |   Encrypted:                 No
|   |   |
|   |   Snapshot:                  CC85FCCB-935B-48A9-9E41-563DA356B255
|   |   Snapshot Disk:             disk3s1s1
|   |   Snapshot Mount Point:      /
|   |   Snapshot Sealed:           Yes

It looks like its already mounted and I confirmed that by doing diskutil mount disk3s1. It says "Sealed: broken". Now I am getting information that I might want to do diskutil apfs repairVolume?

I've done quite a bit given how new I am to this. Can someone please explain everything going on here on a conceptual level? I feel like my disk can not truly be that messed up, I must have just don't some odd little command at one point that did something odd.

Also, I earlier checked that my computer could actually mount a .dmg and run it, and it worked fine - in the command line, I went to my /Downloads directory, found the .dmg file that I had downloaded, did sudo chmod 755 to give it execution permissions, used hdiutil attach, cd'ed into the mount point, found the actual app file, and ran it with ./app. And it launched. So I know I can actually run .dmg files. I just can't double click them in Safari or install stuff from brew.

So clearly there is some very particular reason for all this and I would appreciate if anyone could fill me in on what is going on and what I can investigate. Thanks.

Answer 1

I just can't double click them [DMG files] in Safari or install stuff from brew.

No, you can't "double-click" DMG files to run from Safari. It's not a filetype Safari knows how to handle. As for installing applications, the typical type of DMG is read-only so you wouldn't be able to write anything to it.

Just double click the DMG in Finder and it should automatically mount the volume and open a Finder window showing the file to be copied or installer to be run.

A DMG file is an Apple Disk Image and is a completely separate entity from your APFS container. To install software, you shouldn't be mounting/dismounting your APFS volumes; it's unclear why you're doing so.

I am pretty sure I was learning how to partition my disk to install Linux and I may have done something with diskutil like unmounting my primary disk.

If you're booted into macOS, you simply cannot unmount your primary drive. You'd need to boot into Recovery to make those changes.

Dual booting an OS has been asked/answered many times and there are excellent guides on how to do this. However, this is unrelated to installing software via Homebrew. As you're new to all of this, I don't advise you go down the dual/multi-boot path just yet. Instead, try things out in a virtual environment (VirtualBox is free). You can run things in "seamless mode" meaning that it appears as if it's running natively rather than in a window. You'll gain valuable experience running things before you take on the challenge of modifying APFS containers and drive partitions.

That said, if you do plan on persuing a dual/multi-boot system, be sure to back everything up before you proceed!

As for installing your Homebrew Apps, it's best to peruse the documentation to gain a familiarity with how things work. However, to summarize, you'd install a package with the command brew install <formulae>. We even have questions/answers on how to install formulae from local files which is what you'd do if you had a DMG with brew formulae/packages contained within it.