How to make a downloaded ISO bootable on Mac OS


This article explains how to make a downloaded ISO file bootable on Mac OS. The test was was an Mac Mini M2 but in theory this should work across all Macs and all versions.


Download the ISO

Download the ISO to a temporary location on your hard drive. For example, if you want to make a Proxmox bootable USB disk, you might download the latest ISO from here:

Start Terminal:

mkdir ~/Desktop/iso
cd ~/Desktop/iso

Convert the ISO

Convert the downloaded ISO file to an .dmg file.

hdiutil convert -format UDRW -o proxmox proxmox-ve_8.2-1.iso
Elapsed Time: 5.270s

Next put the USB disk into the Mac’s USB port.

Figure out the USB disk number

The best way to figure out the disk number is to carefully observe the disk size written on the USB disk. If your disk is 8 GB the output won’t display exactly 8GB, for example, it might display 7.8 GB. Also look for asterisks. If you’re still unsure, put the disk in, run the utility. Take the disk out again, and run the utility again. You’ll see something is now missing.

This disk number is important because it will be used throughout the rest of this tutorial.

diskutil list
/dev/disk7 (external, physical):
0: GUID_partition_scheme *7.8 GB disk7

On my system, disk7 was the USB disk which I only knew because I could compare the sizes with what I already knew was there. The disk name is important because it’s used in the next step.

Unmount the disk:

diskutil unmountDisk /dev/disk7
Unmount of all volumes on disk7 was successful

Use dd as sudo to make an input file and output file of block size 1m. Please note this could take a while, for example, for example on the Mac Mini M2 50 seconds for 1 gigabyte, and up to 4 minutes for 1.6 gigabytes.

Note: The output file (of) below rdisk7. The 7 is important because it’s the disk number you obtained earlier.

sudo dd if=proxmox.dmg of=/dev/rdisk7 bs=1m
1395881984 bytes transferred in 213.717118 secs (6531447 bytes/sec)

In the above procedure, if you get the disk number wrong, you might end up with something like this:

dd: /dev/rdiskX: Operation not permitted

Eject the disk

diskutil eject /dev/disk7

The job is done.


Struggling to format your USB disk?

“Couldn’t modify partition map.” or “Couldn’t modify partition map. : (-69874)”

Do this in a terminal:

diskutil list

Identify the disk. If you’re still unsure, pull disk disk out, and see what changed.


diskutil eraseDisk FAT32 USB /dev/disk7



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