From UntangleWiki

The standard way to install Untangle is by burning the Untangle ISO CD-ROM image and booting from that, however many people are installing onto PCs without a CD-ROM drive. This guide shows you how to install Untangle from a USB stick. All existing data on the USB stick will be destroyed. Be careful with these instructions as you can easily overwrite another device (such as your hard drive) if you're not paying attention.

Contents 1 Prerequisites 2 Windows Users 3 Linux Users

Prerequisites

• The latest Untangle ISO
• Please see the latest release thread in our Announcements forum for the latest USB images
• A USB stick

Windows Users

1. Download RMPrepUSB software RMPrepUSB.
2. Install RMPrepUSB on your Windows computer.
3. Download Untangle image from above images.
4. Launch RMPrepUSB on your Windows computer.
5. Plug your USB stick to your computer .
6. Verify the USB is the target and NOT your main hard drive(top red arrow in picture below).
7. Click on the "File -> Drive" button to select the image and start the creation of your Untangle USB install stick.
8. Once done click on "Eject Drive" to remove the USB stick and start the Untangle install steps

Linux Users

You will first need to figure out what block device your USB stick is using - simply insert it and run dmesg, then look for sdX where X is the device. Here's the tail end of the output of dmesg after inserting my USB stick:

[870752.937990] scsi18 : usb-storage 1-2.1.4:1.0
[870753.936829] scsi 18:0:0:0: Direct-Access     USB 2.0  Flash Disk       5.00 PQ: 0 ANSI: 2
[870753.961089] sd 18:0:0:0: Attached scsi generic sg5 type 0
[870753.965288] sd 18:0:0:0: [sde] 2009088 512-byte logical blocks: (1.02 GB/981 MiB)

I know my USB stick is 1GB, so that's the one. if my Untangle .img is in ~/Downloads/, I can run:

hlarsen@hDesk:~$ sudo dd if=Downloads/untangle_920_build5_x32.img of=/dev/sde bs=1M

to write the image to the USB stick. You'll need to swap out if= with your .img's location and of= with your USB stick's block device.