1. Visit Centos’ web page, https://www.centos.org/download/, and download the iso image you’d like to boot from.
2. When the download has completed, open up terminal and use ‘hditutil’ to convert the *.iso to an *.img file (specifically, a UDIF read/write image).
$hdiutil convert -format UDRW -o target.img CentOS-7.0-1406-x86_64-Everything.iso
Reading Master Boot Record (MBR : 0)…
Reading CentOS 7 x86_64 (Apple_ISO : 1)…
Reading (Type EF : 2)…
Reading CentOS 7 x86_64 (Apple_ISO : 3)…
…………………………………………………………………….
Elapsed Time: 33.590s
Speed: 200.5Mbytes/sec
Savings: 0.0%
created: /tmp/target.img.dmg
3. Use the ‘dd’ utility to copy the iso to your USB drive:
$ diskutil list
/dev/disk0
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *121.3 GB disk0
1: EFI EFI 209.7 MB disk0s1
2: Apple_HFS Macintosh HD 120.5 GB disk0s2
3: Apple_Boot Recovery HD 650.0 MB disk0s3
/dev/disk1
#: TYPE NAME SIZE IDENTIFIER
0: FDisk_partition_scheme *31.9 GB disk1
1: DOS_FAT_32 NO NAME 31.9 GB disk1s1
/dev/disk2
#: TYPE NAME SIZE IDENTIFIER
0: CentOS_7.0_Final *4.5 GB disk2
$ diskutil unmountDisk /dev/disk1
Unmount of all volumes on disk1 was successful
$ diskutil unmountDisk /dev/disk2
Unmount of all volumes on disk2 was successful
$ time sudo dd if=target.img.dmg of=/dev/disk1 bs=1m
Password:
4261+0 records in
4261+0 records out
4467982336 bytes transferred in 1215.483272 secs (3675890 bytes/sec)