append initrd=/ubninit ks=cdrom:/ks_default.cfg ramdisk_size=8192
and change it to:
append initrd=/ubninit ks=hd:sdb1:/ks_default.cfg ramdisk_size=8192
The original line instructs the Linux installer to look for the configuration file in the CDROM, we changed that to make it look for the file in a hard drive (SDB1), the 1 at the end is the partition, sdb1 is the second hard drive's first partition. If you have more than one hard drive you would have to modify the line. As we only have one hard drive (sda) the usb is the second hard drive (sdb), if you have 2 hard drives then the USB would be the third hard drive (sdc).
That is all for the first file, save it and close it.
Now let's look for the file ks_default.cfg in the USB root and open it with Notepad++
Look for this lines:
#Use CDROM installation media
cdrom
and change it to:
#Use CDROM installation media
#cdrom
we comment the cdrom line because we are not going to install from cdrom.
Now append this line after the CDROM section
ignoredisk --drives=sdb
This line tells the Linux Installer to ignore the USB as a target for installation, we won't install to the USB we are going to install to the hard drive.
Now look for this line, is right below:
#System bootloader configuration
bootloader --location=mbr
and change it to:
#System bootloader configuration
bootloader --location=mbr --driveorder=sda,sdb
This change is very important, it tells the Linux installer that the computer boots first from sda (the hard drive), so it installs the bootloader there. If you miss this change, the linux installer will install the bootloader in the USB, so you would only be able to boot Elastix if the USB is connected.
That's it for the second file, save it and close it.
7. We are ready to start the installation. Plug in the USB drive in the computer and turn it on. As we only have one unpartitioned hard drive, the PC should boot directly from the USB. If it doesn't, load the computer boot menu and select the USB to boot.
8. You should see the screen below, just hit Enter to continue.

9. Select your installation language and hit enter to continue.
10. Select the keyboard layout and hit enter to continue.
11. In the next screen select Hard Drive and enter to continue.
12. Now, if you are using the same configuration as me (one unpartitioned hard drive), you should get only one choice here /dev/sdb1 (arrow 1) which is the USB, if your hard drive already have partitions or you have more than one hard drive you will probably get a list here. You should select the USB, usually it is the last one in the list.
If you copied the Elastix ISO to the USB root just leave the directory blank (arrow 2), if you copied it to a directory, specify it there and the click OK to continue.