Howto make a bootable USB stick on OS X

By | 2016/01/28

Recently I updated my Windows PC (which I only use for gaming purpose of course) and managed to screw it. Once I did the planned restart it showed me “No operating system found”. Since I upgraded from Windows 7 to Windows 10 via the update manager I also did not had a Windows 10 image available to recover the system.

Thanks that I still have my Mac, and I am even more thankful, that it understands most of the Unix/Linux commands. So to get back to my old life, I first downloaded the Windows 10 ISO image from the Microsoft Homepage [1].

Okay so we have an ISO image – how to we get it on an USB stick – a simple copy would not make it. Therefore the following steps are required.

1.) Identify your USB stick – you would not like to replace your data storage or your OS X system.

This I usually do via the mount command:

jvr-mac:~ jvr$ mount
/dev/disk1 on / (hfs, local, journaled)
devfs on /dev (devfs, local, nobrowse)
map -hosts on /net (autofs, nosuid, automounted, nobrowse)
map auto_home on /home (autofs, automounted, nobrowse)
/dev/disk2s1 on /Volumes/Data (exfat, local, nodev, nosuid, noowners)
/dev/disk3s1 on /Volumes/ESD-USB (msdos, local, nodev, nosuid, noowners)

And here we go /dev/disk3s1 is the drive I was searching for. To be sure – double check it in the Finder App.

2.) Convert the .iso image to an .dmg image by using hdiutil

jvr-mac:~ jvr$ hdiutil convert -format UDRW -o Win10.dmg Downloads/Win10_1511_German_x64.iso
J_CCSA_X64FRE_DE-DE_DV5          (Apple_UDF : 0) lesen …
........................................................................................................
Dauer:  1m  2.901s
Geschwindigkeit: 61.0M Byte/s
Ersparnis: 0.0 %
created: /Users/jvr/Win10.dmg

The last sentence looks promising!

3.) Unmount the USB stick

jvr-mac:~ jvr$ diskutil umount /dev/disk3s1 
Volume ESD-USB on disk3s1 unmounted

4.) Write the image to your USB stick using dd command

This is the most critical part – so be sure that you write the image on the correct drive/stick. Just for your information: if stands for input file, of for output file and bs is the blocksize. The dd command basically copies block by block to the new drive.

jvr-mac:~ jvr$ sudo dd if=Win10.dmg of=/dev/disk3s1 bs=10m

5.) Unmount USB stick again

jvr-mac:~ jvr$ diskutil unmountDisk /dev/disk3s1

And by now you should have a bootable USB stick to recover your system. Lets cross the fingers that everything will work out fine with the PC 🙂

[1] Microsoft, Windows 10 ISO Image

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