For the Mac

1. Download the Ubuntu MATE distribution from ubuntu-mate.org. (You'll need to download the correct version for your computer, probably 64-bit for a modern computer.) I downloaded ubuntu-mate-16.04.3-desktop-amd64.iso for my USB flash drive.

2. On the Mac, you'll need to convert this .iso into a format that will work on our machines. In the Terminal, navigate to where you downloaded the .iso drive and issue the following command (in bold):
   

   rwhite@MotteRouge:~/Downloads$ hdiutil convert -format UDRW -o linuxmint-17.1-cinnamon-64bit linuxmint-17.1-cinnamon-64bit.iso

   Pretty quickly, you'll see the the dmg version of the iso file appear:

   rwhite@MotteRouge$ hdiutil convert -format UDRW -o ubuntu-mate-16.04.3-desktop-amd64 ubuntu-mate-16.04.3-desktop-amd64.iso Reading Driver Descriptor Map (DDM : 0)… Reading Ubuntu-MATE 16.04.3 LTS amd64 (Apple_ISO : 1)… Reading Apple (Apple_partition_map : 2)… Reading Ubuntu-MATE 16.04.3 LTS amd64 (Apple_ISO : 3)… Reading EFI (Apple_HFS : 4)… Reading Ubuntu-MATE 16.04.3 LTS amd64 (Apple_ISO : 5)… .............................................................................. Elapsed Time: 9.226s Speed: 178.6Mbytes/sec Savings: 0.0% created: /Users/rwhite/Downloads/ubuntu-mate-16.04.3-desktop-amd64.dmg
3. Plug in an empty USB flash drive (I used a 16GB USB 3 drive from Kingston), launch Disk Utility on your Mac, select the Erase option, and reformat your flash drive to a "Mac OS Extended (Journaled)" file system with a Scheme of "Master Boot Record." If the reformatting fails the first time (it does on my machine running macOS Sierra), try again and it should go through the second time.
   
4. Identify the location of that flash drive on your computer by using the diskutil command in the Terminal:
   rwhite@MotteRouge:~/Downloads$ diskutil list /dev/disk0 (internal, physical): #: TYPE NAME SIZE IDENTIFIER 0: GUID_partition_scheme *500.3 GB disk0 1: EFI EFI 209.7 MB disk0s1 2: Apple_CoreStorage MotteRouge 499.4 GB disk0s2 3: Apple_Boot Recovery HD 650.0 MB disk0s3 /dev/disk1 (internal, virtual): #: TYPE NAME SIZE IDENTIFIER 0: Apple_HFS MotteRouge +499.0 GB disk1 Logical Volume on disk0s2 457C9A8B-4F7F-48C3-85B5-F1AF141DA2DE Unencrypted /dev/disk2 (external, physical): #: TYPE NAME SIZE IDENTIFIER 0: FDisk_partition_scheme *15.5 GB disk2 1: Apple_HFS MATE 15.5 GB disk2s1
   Here, I can see that my flash drive is located in /dev/disk2
5. Unmount the flash drive by referring to the drive location for your computer.
   rwhite@MotteRouge:~/Downloads$ diskutil unmountDisk /dev/disk2 Unmount of all volumes on disk2 was successful
6. Finally, copy the .dmg file you created earlier to your unmounted flash drive using the dd command. This will take a few minutes to happen, depending on the speed of your computer and flash drive. (Note that when you enter your password, there will be no indication that you are entering any characters. That's okay.
   rwhite@MotteRouge:~/Downloads$ sudo dd if=ubuntu-mate-16.04.3-desktop-amd64.dmg of=/dev/rdisk2 bs=1m Password: 1648+0 records in 1648+0 records out 1728053248 bytes transferred in 143.224451 secs (12065351 bytes/sec) rwhite@MotteRouge:~/Downloads$
   Once the process has completed, OS X may pop up a dialog box that says the flash drive was unreadable. That's okay. Select "Eject" and take out the USB flash drive, which you can now use to boot into Ubuntu MATE.

7. To boot into Linux, place the USB flash drive into your Mac, and start/restart the machine. Hold down the Option key during the startup process, and you'll eventually be asked which drive you'd like to use to boot up. Select the EFI drive and wait a few minutes. Soon you'll be running Linux on the flash drive. Do NOT choose "Install Ubuntu MATE" from the destktop—it will wipe out your OS X drive, and you don't want that to happen!!! :)
8. Enjoy playing with Linux!
   Not sure what to do next? Check out Try Linux!

For the PC

Coming soon.