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MacOS Terminal: Create a Bootable USB from an ISO Using "dd"

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By: kedlogic
February 28, 2017
usb-bootThe .ISO file is a widely used disk image format and the standard format for bootable media. (Linux anyone?)Here is a quick and easy way to make a bootable USB from a .ISO file, no 3rd party apps required.Here are the terminal commands in order, followed by explanations of what they do:

Note: You'll need to be an administrator to do this.

diskutil listLists out all disk drives and their volumes. Drives are labeled as disk0, disk1, disk2, etc. Volumes are labeled disk1s0, disk1s1, disk1s2, etc. For our purposes, we only care about the drive. In this case, we're going to assume our flash drive is disk2.diskutil unmountDisk disk2The unmountDisk command unmounts all volumes of the given disk drive but keeps the drive itself visible to the computer (as opposed to the eject option that disconnects it entirely)sudo dd if=/Users/kyle/Downloads/Linux.iso of=/dev/disk2 bs=8m"sudo" tells the system to use root level (that is the system's highest level) privileges to perform the following action."dd"  is an extremely basic, but powerful block level copy command built into all Linux and Unix operating systems (MacOS is UNIX based)"if" stands for input file (a.k.a the source file or location). In our use-case, this is the .ISO file. In MacOS, if you have a finder window open, you can drag and drop the .iso into the terminal and it will auto-fill this file path."of" stands for "output file" (a.k.a the destination file or location). For us, this is our USB drive, disk2. The specific path for external drives is in "/dev", hence /dev/disk2"bs" stands for block size. dd copies data in blocks rather than on a file by file basis (this is why it's so fast) and this command gives you the option to set how big each block is. There is a science to the ideal block size, but I don't know it. 8m (MegaBytes) has consistently worked well for my uses.The command will not show any progress until it's done, but you can press control+t for status updates. With an average computer, this takes less than 5min to complete.Once complete:diskutil eject disk2The USB drive can now safely be removed. Assuming that the iso is EFI-compatible, you can reboot your mac to test it.   
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