How To Create USB Boot Stick for Mac

Step 1: Prepare your USB Stick (format)

Select the USB drive (External)

Format: Mac OS Extended (Journal)

Scheme: GUID Partition Map

Hit Erase.

Step 2: Download ISO

Here we downloaded an ISO with Ubuntu. https://www.ubuntu.com But you can choose whatever you want.

Step 3: Convert ISO to UDRW for Mac booting

Check ISO file type:

$ file ubuntu-18.04.2-desktop-amd64.iso 
ubuntu-18.04.2-desktop-amd64.iso: ISO 9660 CD-ROM filesystem data (DOS/MBR boot sector) 'Ubuntu 18.04.2 LTS amd64' (bootable)
$

Convert ISO to UDRW (This can take about 1 to 3 minutes to complete):

$ hdiutil convert -format UDRW -o ubuntu-18.04.2-desktop-amd64.img ubuntu-18.04.2-desktop-amd64.iso
Reading Driver Descriptor Map (DDM : 0)…
Reading Ubuntu 18.04.2 LTS amd64 (Apple_ISO : 1)…
Reading Apple (Apple_partition_map : 2)…
Reading Ubuntu 18.04.2 LTS amd64 (Apple_ISO : 3)…
....................................................................................................................................................................................................................................
Reading EFI (Apple_HFS : 4)…
.....................................................................................................................................................................................................................................
Reading Ubuntu 18.04.2 LTS amd64 (Apple_ISO : 5)…
........................................................................................................................................................................................................................................
Elapsed Time: 2m 44.666s
Speed: 11.6Mbytes/sec
Savings: 0.0%
created: /Volumes/<your-path>/ubuntu-18.04.2-desktop-amd64.img.dmg
$

Check the file type

$ file ubuntu-18.04.2-desktop-amd64.img.dmg
ubuntu-18.04.2-desktop-amd64.img.dmg: ISO 9660 CD-ROM filesystem data (DOS/MBR boot sector) 'Ubuntu 18.04.2 LTS amd64' (bootable)
$

Step 4: See where your USB drive is mounted

$ diskutil list
/dev/disk3 (external, physical):
#: TYPE NAME SIZE IDENTIFIER
0: GUID_partition_scheme *15.9 GB disk3
1: EFI EFI 209.7 MB disk3s1
2: Apple_HFS Ubuntu 15.6 GB disk3s2
$

So your USB drive physical device is /dev/disk3. You will get a different value here. Not it down.

Step 5: Unmount USB drive

Unmount it (do not eject it!)

Replace /dev/diskX with your value in step 4.

$ diskutil unmountDisk /dev/diskX
Unmount of all volumes on disk3 was successful
$

Step 6: Write ISO to USB (will take about 5 Minutes)

Note: sudo stands for super user do, dd stands for disk dump, if stands for input file, of for output file, bs for Block Size. 1m for 1 Mega byte.

$ sudo dd if=ubuntu-18.04.2-desktop-amd64.img of=/dev/rdiskX bs=1m
sudo dd if=ubuntu-18.04.2-desktop-amd64.img.dmg of=/dev/rdisk3 bs=1m
Password:
1904+0 records in
1904+0 records out
1996488704 bytes transferred in 175.236257 secs (11393126 bytes/sec)
$

Step 7: Eject USB drive

Eject USB drive

$ diskutil eject /dev/diskX
Disk /dev/disk3 ejected
$

Done. You can now remove the USB stick.

Note: If you insert this stick into your Mac a message will appear saying that it can not be read by the system. This is normal, just hit Ignore.
This disk you inserted was not readable by this computer. Hit Ignore.