How to convert macOS installer to bootable ISO using disk utility?

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macOS installer.app have to be converted to .iso image to be used in Virtual machines (such as Virtualbox, VMware, …)

When you download any macOS installer, it comes in the form of installer .app you can follow the steps described in this tutorial to convert installer .app to .DMG then .ISO

1) Using disk utility as described in this video.
2) Using terminal commands.
3) Using third party application.

just follow the steps described carefully: –

Converting a macOS installer .app file (e.g., Install macOS Ventura.app) to a .dmg and then to a bootable .iso using Disk Utility is an alternative to Terminal-based methods. This process leverages Disk Utility’s graphical interface to create a disk image, make it bootable with the installer’s createinstallmedia tool (via Terminal), and then convert it to an ISO. Below is a step-by-step guide tailored for macOS, using Disk Utility where possible.

Prerequisites

macOS Installer: A full .app file (e.g., Install macOS Ventura.app) in /Applications. Download from the Mac App Store or gibMacOS if needed.
Mac with Disk Utility: Any macOS version compatible with the installer (e.g., 10.13+ for Ventura).
Free Space: At least 20GB (installer ~12GB + working space).
USB Drive or Space for Image: A USB drive (optional) or enough disk space for a 14GB .dmg.
Admin Access: Needed for createinstallmedia in Terminal.

Step-by-Step Instructions to create bootable iso using disk utility?

Step 1: Locate the macOS Installer

Verify the Installer:
Open Finder, go to /Applications, and confirm Install macOS Ventura.app is present.
Right-click > Get Info—size should be ~12-13GB.
Move if Needed:
If it’s elsewhere (e.g., ~/Downloads), drag it to /Applications.

Step 2: Create a Blank `.dmg` Using Disk Utility

Open Disk Utility:
Go to Applications > Utilities > Disk Utility or search via Spotlight (Command + Space, type “Disk Utility”).
Create a New Image:
Click File > New Image > Blank Image from the menu bar.
Configure the Image:
Save As: Ventura (saves as Ventura.dmg).
Where: Choose a location (e.g., ~/Desktop).
Name: VenturaISO (volume name when mounted).
Size: 14GB (enter “14” in the field, select “GB” from the dropdown—Ventura needs ~12GB+).
Format: Mac OS Extended (Journaled) (required for createinstallmedia).
Encryption: None.
Partitions: Single partition - GUID Partition Map.
Image Format: read/write disk image (not sparse—ensures compatibility).
Click Save.
Result:
Disk Utility creates Ventura.dmg (e.g., ~/Desktop/Ventura.dmg) and mounts it as /Volumes/VenturaISO.

Step 3: Make the `.dmg` Bootable

Note: Disk Utility can’t directly make a bootable installer—use Terminal’s createinstallmedia for this step.
Run createinstallmedia:
Open Terminal (Applications > Utilities > Terminal).
Enter:
sudo /Applications/Install\ macOS\ Ventura.app/Contents/Resources/createinstallmedia --volume /Volumes/VenturaISO --nointeraction
Enter your admin password.
Process takes 10-20 minutes—Terminal shows “Copying installer files…” and ends with “Install media now available at /Volumes/Install macOS Ventura”.
Result: The .dmg is now bootable, renamed to /Volumes/Install macOS Ventura.

Step 4: Unmount the `.dmg`

Unmount in Disk Utility:
In Disk Utility’s sidebar, find “Install macOS Ventura” under your Ventura.dmg image.
Click the eject icon (⏏) next to it, or right-click > Eject.
Verify:
Check Finder or Terminal (ls /Volumes/)—it should no longer appear.

Step 5: Convert `.dmg` to `.iso` Using Disk Utility

Convert the Image:
In Disk Utility, click Images > Convert from the menu bar.
Select Ventura.dmg (e.g., ~/Desktop/Ventura.dmg) > Open.
In the dialog:
- Save As: VenturaISO (saves as VenturaISO.dmg—we’ll rename later).
- Where: ~/Desktop.
- Image Format: DVD/CD master (this creates a .cdr file, equivalent to ISO).
- Encryption: None.
Click Convert.
Result:
Outputs VenturaISO.cdr (e.g., ~/Desktop/VenturaISO.cdr), a bootable CD/DVD master image.

Step 6: Rename `.cdr` to `.iso`

Rename:
In Finder, right-click VenturaISO.cdr > Rename > Change to Ventura.iso.
Or in Terminal:
mv ~/Desktop/VenturaISO.cdr ~/Desktop/Ventura.iso
Why: .iso is more universally recognized by VM software (though .cdr works in many cases).

Step 7: Clean Up

Remove Original .dmg:
Delete Ventura.dmg if space is needed:
rm ~/Desktop/Ventura.dmg
Verify ISO Size:
Right-click Ventura.iso > Get Info—should be ~12-14GB.

Step 8: Test the ISO (Optional)

VirtualBox:
Create a new VM > Attach Ventura.iso under Storage > Start. It should boot to the Ventura installer.
VMware:
Attach to a VM > Boot and confirm.

Troubleshooting

“createinstallmedia” Fails:
Ensure the .dmg format is Mac OS Extended (Journaled)—recreate if APFS.
Verify installer integrity (re-download if <12GB).
“Volume Busy” on Eject:
Quit apps accessing /Volumes/Install macOS Ventura, or force eject in Terminal:
hdiutil detach /Volumes/Install\ macOS\ Ventura -force
ISO Not Bootable:
Confirm createinstallmedia completed—rerun if interrupted.
Use DVD/CD master format, not read/write, in conversion.
Disk Utility Errors:
Ensure enough free space (20GB+). Restart Disk Utility if it hangs.

Notes

Disk Utility Limits: It can’t make the .dmg bootable directly—Terminal bridges this gap.
Alternative: Terminal-only methods (e.g., hdiutil) are faster but less GUI-based—see prior answers if preferred.
Use Case: The .iso works for VMs (VirtualBox, VMware) or burning to DVDs (rare).

2) Convert .app to .dmg then .iso using terminal commands and parallels desktop app:-

these are the terminal commands used in the following video: –
a] hdiutil create -o ………… -size 15000m -layout SPUD -fs JHFS+
,b] hdiutil attach ………… -noverify -nobrowse -mountpoint /Volumes/installer_goes_here
c] asr restore -source ………………. -target /Volumes/installer_goes_here -noprompt -noverify -erase
d] hdiutil detach ………….
e] hdiutil convert …….. -format UDTO -o ……..