How to install linux with a usb device

http://www.ibm.com/support/knowledgecenter/en/linuxonibm/liabw/liabwinstallusb.htm

Procedure

Download the ISO file for the Linux distribution and create a bootable USB device or DVD.

Insert your USB device into the front USB port.

Verify that USB device is shown as an option in Petitboot as USB: sdc:

USB: sdc /
Rescue mode
Install

Note: Select Rescan devices if USB device does not appear.

If you are installing Red Hat Enterprise Linux 7.2, you must provide some additional details to the installer. Follow these steps:

Record the UUID of the USB device. For example, the UUID of the USB device in the following example is 2015-10-30-11-05-03-00.

[USB: sdb1 / 2015-10-30-11-05-03-00]
Rescue a Red Hat Enterprise Linux system (64-bit kernel)
Test this media & install Red Hat Enterprise Linux 7.2  (64-bit kernel)
*  Install Red Hat Enterprise Linux 7.2 (64-bit kernel)

Select Install Red Hat Enterprise Linux 7.2 (64-bit kernel) and press e (Edit) to open the Petitboot Option Editor window.

Move the cursor to the Boot arguments section and add the following information:

inst.stage2=hd:UUID=your_UUID

where your_UUID is the UUID that you recorded.

Petitboot Option Editor
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Device:    ( ) sda2 [f8437496-78b8-4b11-9847-bb2d8b9f7cbd]
(*) sdb1 [2015-10-30-11-05-03-00]
( ) Specify paths/URLs manually

Kernel:         /ppc/ppc64/vmlinuz
Initrd:         /ppc/ppc64/initrd.img
Device tree:
Boot arguments: ro inst.stage2=hd:UUID=2015-10-30-11-05-03-00

[    OK    ]  [   Help   ]  [  Cancel  ]

Select OK to save your options and return to the Main menu.

Select Install.
Note: Be patient! It can sometimes take a couple minutes for the installation to begin.

Follow the installation wizard for your Linux distribution to set up disk options, your user name and password, time zones, and so on. The last step is to restart your system.

After the system restarts, Petitboot displays the option to boot the Linux distribution that you installed. Select this option and press Enter.