Mac Low-Level Write on an USB Drive

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Internal

Overview

This is the procedure to write an USB drive at low level with dd. This is sometimes necessary when we want to create a bootable USB drive, for example.

Procedure

Insert the USB drive in the drive, the system will mount it and expose it automatically.

Identify the device the USB drive was associated with: 

mount

/dev/disk1s1 on / (apfs, local, journaled)
devfs on /dev (devfs, local, nobrowse)
/dev/disk1s4 on /private/var/vm (apfs, local, noexec, journaled, noatime, nobrowse)
map -hosts on /net (autofs, nosuid, automounted, nobrowse)
map auto_home on /home (autofs, automounted, nobrowse)
/dev/disk3s1 on /Volumes/NOVA ORDIS (msdos, local, nodev, nosuid, noowners)

The device associated with USB can also be identified with Disk Utility:

DiskUtility.png

Unmount with diskutil: 

diskutil unmount /dev/disk3s1

Write with dd: 

dd if=/Users/ovidiu/Desktop/rhel-server-7.6-x86_64-dvd.iso of=/dev/disk3s1
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