Converting the USB .img file to boot
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The FreePBX Distro has a USB version of each ISO. Â You can download the xxx.img image to your local computer from http://www.freepbx.org/downloads. Â Once downloaded, you will need to use the dd command (disk cloning) to transfer the file onto your USB drive. Â Follow the steps below for Windows or Mac/Linux.
Windows
Windows users will need to download a utility that can create a USB-bootable image from the .img file.  Please download the latest version of Win32DiskImager that ends in -binary.zip.
Next, launch Win32DiskImager. Use the browse button to navigate to the location of the .img file. Insert a USB thumb drive and select its drive letter (in this example, drive E). Click the Write button. The image will be written to the USB thumb drive.
Once completed, you should see a message like this:
NOTE: If the burned image fails to boot, wipe the USB stick before trying a second burn using a utility such as Active@ KillDisk. Otherwise, the second burn attempt will fail since Windows does not understand the GPT partition that was written from the image file. Be very careful that you specify the USB stick when using a wipe utility!
Mac or Linux
First you need to find the USB drive on your local Mac computer with the following command:
Disk
diskutil list |
 It should return something like what is shown below. In our example we can see the USB device is mounted as a DOS_FAT_32 under /dev/disk1
Return
MacBook-Pro:~ tony$ diskutil list
/dev/disk0
   #:                      TYPE NAME                   SIZE      IDENTIFIER
   0:     GUID_partition_scheme                       *750.2 GB  disk0
   1:                       EFI                        209.7 MB  disk0s1
   2:                 Apple_HFS Macintosh HD           749.3 GB  disk0s2
   3:                Apple_Boot Recovery HD            650.0 MB  disk0s3
/dev/disk1
   #:                      TYPE NAME                   SIZE      IDENTIFIER
   0:    FDisk_partition_scheme                       *4.1 GB    disk1
   1:                DOS_FAT_32 NO NAME                4.1 GB    disk1s1 |
 Now, unmount the disk using the command below. Remember to replace the disk number with the id of your USB stick.
unmount
diskutil unmountDisk /dev/disk1 |
 You should see something like this:
unmount
Use the dd command to write. Again, be sure to replace the disk number with the id of your USB stick. Replace if=Desktop/FreePBX-3.211.63-9-x86_64-Full-1368057023.img with the path to your ISO image. This step may take 10-15 minutes to complete.
DD
When complete, you should see a confirmation like the one below:Â
DD
Now you can go boot your PBX from the USB image and go through the normal ISO installer process, skipping steps 1-3 and starting with step 4 where it asks you which version of Asterisk you would like to install.