I’m running Mac OS Sierra and I needed to make a bootable CentOS 7 USB stick.
I downloaded the minimal ISO and proceeded to follow the instructions at How to Copy an ISO to a USB Drive from Mac OS X with dd, but it never worked. The server never recognized the USB stick as valid media.
At first, I thought it might have had to do with the formatting of the USB stick, which was FAT32. So I tried Mac OS Extended and Extended FAT, but that didn’t help either.
As mentioned by a couple of the comments on that page, I tried writing to disk2 instead of disk2s1 (keep in mind that the USB key on your system may be a different disk — use diskutil list to help identify it):
$ diskutil unmount disk2s1
disk2s1 was already unmounted
$ sudo dd if=~/Downloads/CentOS-7-x86_64-Minimal-1611.iso of=/dev/rdisk2 bs=1m
Once it finishes copying, it should look like this:
$ diskutil list
/dev/disk2 (external, physical):
#: TYPE NAME SIZE IDENTIFIER
0: FDisk_partition_scheme *16.1 GB disk2
1: 0xEF 6.4 MB disk2s2