Create a CentOS installation USB key with dd command

1. Prepare an USB key.

2. Copy the iso to the USB with dd command:
[Warning!!] This will overwrite all the existing data on the disk.

> sudo dd if=CentOS-7-x86_64-DVD-1708.iso of=/dev/sdb bs=1M status=progress
4519362560 bytes (4.5 GB) copied, 906.896074 s, 5.0 MB/s    
... (wait)
4312+0 records in
4312+0 records out
4521459712 bytes (4.5 GB) copied, 1240.27 s, 3.6 MB/s

Note:
Set the output stream to /dev/sdx instead of /dev/sdbx.

3. Verfiy with fdisk
> sudo fdisk -l
...
Disk /dev/sdb: 31.0 GB, 30998003712 bytes, 60542976 sectors
Units = sectors of 1 * 512 = 512 bytes
Sector size (logical/physical): 512 bytes / 512 bytes
I/O size (minimum/optimal): 512 bytes / 512 bytes
Disk label type: dos
Disk identifier: 0x1302a8b3

   Device Boot      Start         End      Blocks   Id  System
/dev/sdb1   *           0     8830975     4415488    0  Empty
/dev/sdb2            2320       20295        8988   ef  EFI (FAT-12/16/32)

...

4. Reboot the computer and you may boot from USB. (hopefully)


Reference:
USB flash installation media (正體中文)
https://wiki.archlinux.org/index.php/USB_flash_installation_media_(%E6%AD%A3%E9%AB%94%E4%B8%AD%E6%96%87)