ISO to USB in MacOS

Sandisk USB

I’d like to follow up on my recent Create Bootable USB from ISO post for MacOS: seems I have missed an important point. This post shows you how to burn ISO to USB in MacOS.

Specifically, I tested my procedure using Macbook and VirtualBox/Parallels VMs but the same bootable USB stick would for some reason not boot on a standard physical PC.

ISO to USB

After a bit more research, I realise now that the following step missing: unlike other operating systems, in MacOS you must convert an ISO image into a different image format, UDRW. If you don’t, your resulting USB stick will not boot (but still have all the valid files).

Convert ISO into bootable image

We convert ISO image into UDRW format using the excellent [hdutil command][hdutil]. I only need cd /Volumes/Stuff/dist command because that’s where I keep my ISO images.

In this example, I’m converting a CentOS 7 bootable DVD ISO:

greys@maverick:/ $ cd /Volumes/Stuff/dist
$ ls -al CentOS*
-rw-r--r--@ 1 greys staff 4521459712 13 Apr 2018 CentOS-7-x86_64-DVD-1708.iso
$ hdiutil convert -format UDRW -o centos CentOS-7-x86_64-DVD-1708.iso
Reading Master Boot Record (MBR : 0)…
Reading CentOS 7 x86_64 (Apple_ISO : 1)…
Reading (Type EF : 2)…
Reading CentOS 7 x86_64 (Apple_ISO : 3)…
.............................................................
Elapsed Time: 10m 15.681s
Speed: 7.0Mbytes/sec
Savings: 0.0%created: /Volume/Stuff/dist/centos.dmg
$ ls -al centos.dmg
-rw-r--r--  1 greys  staff  4520542208  2 Jan 17:54 centos.dmg

Burn image to make bootable USB stick in MacOS

As in the original bootable USB from ISO procedure for Mac, we’ll use dd command:

As you remember, dd command needs 3 parameters for our scenario:

• if – specifying the image we’d like to burn
• of – specifying the destination device, a USB disk /dev/disk9 in our case
• bs – a large enough block size, 1m (means 1 MegaByte)

here’s how we use dd to burn centos.dmg:

$ sudo dd if=./centos.dmg of=/dev/disk9 bs=1m
4311+1 records in
4311+1 records out
4520542208 bytes transferred in 1486.155206 secs (3041770 bytes/sec)

That’s it! The USB stick is ready, you can use it with a VM or physical desktop – it will definitely boot now!

pS: I’ll update the original ISO to bootable USB on Mac page as well.

See Also

• MacOS and OSX versions
• Creating Bootable USB from ISO in MacOS
• How To: Mount DMG using hdiutil
• Bootable USB from ISO with Etcher