Ubuntu – How to reinstall ubuntu 14.04 without cd drive or usb

if you are using ubuntu now, try the application "startup disk creator"

if you are currently on windows, i have found an application called "rufus" works very well

if you still cant get the USB to boot, it may be a problem with your bios configuration being incompatible how the USB was formatted... Such an issue woud be beyond my expertise...

I don't know about downgrading ubuntu without like running into some serious problems, even upgrading ubuntu "in-place" used to cause problems often too, but backing up your home (and other important files) and then installing a new (or in this case old) version should work.

You could try fixing the usb stick to make it bootable, using gparted or fdisk should be able to set the bootable flag on the usb stick, if that's the only problem.

Sometimes the live-usb creators just don't work, you could try another different method of making a bootable usb stick, like using unetbootin or plain dd, but I really like the multi-iso method that pendrivelinux.com suggests, it works from the terminal of any linux, and you can add new iso's (if the drive has space) by just copying the whole iso and editing one grub text file. It's at http://www.pendrivelinux.com/boot-multiple-iso-from-usb-via-grub2-using-linux/ and there are programs that should do something similar if you don't want to DIY.

They recommend formating the usb to a single partition, but this isn't really necessary if you can get grub to boot & work from the 1st partition. Most usb drives come from the factory as a single partition anyway so should be ready to go, or you can use gparted to (format if needed and) make the usb bootable (set bootable flag) too.

Here's the key parts, to get grub onto the usb & setup:

1. Mount the usb - Type mkdir /mnt/USB && mount /dev/sdx1 /mnt/USB (replacing x with your actual usb device)
2. Type grub-install --force --no-floppy --boot-directory=/mnt/USB/boot /dev/sdx (replacing x with your actual USB device, often sda or sdb etc... but NOT the partition sda1 or sdb1)
3. Type cd /mnt/USB/boot/grub (to change directory)
4. Download the demo grub.cfg - Can use web browser to save it or wget: Type wget pendrivelinux.com/downloads/multibootlinux/grub.cfg (to get the grub.cfg file)

The grub.cfg is basically this, with a few more/different examples, can copy & paste this and edit to fit your specific iso's instead of wget/download, and put this into the usb's boot/grub/grub.cfg:

# This grub.cfg file was created by Lance http://www.pendrivelinux.com
# Suggested Entries and the suggestor, if available, will also be noted.

set timeout=10
set default=0

menuentry "Ubuntu Desktop ISO" {
 loopback loop /ubuntu.iso
 linux (loop)/casper/vmlinuz boot=casper iso-scan/filename=/ubuntu.iso noeject noprompt splash --
 initrd (loop)/casper/initrd.lz
}

menuentry "Linux Mint ISO" {
 loopback loop /linuxmint.iso
 linux (loop)/casper/vmlinuz file=/cdrom/preseed/mint.seed boot=casper initrd=/casper/initrd.lz iso-scan/filename=/linuxmint.iso noeject noprompt splash --
 initrd (loop)/casper/initrd.lz
}

Parts to edit are the name of the iso, change "ubuntu.iso" or "linuxmint.iso" to the actual iso name you've downloaded, and the menuentry title to be more descriptive.

Then just download a live iso and copy it to the usb's root. Or you could even put them in an iso directory, but then you'd have to chance references to "/ubuntu.iso" into /iso/ubuntu.iso". And you can put as many different live iso's to try as will fit on your usb.

And, you should be able to get this method to work by copying the iso to a partition on your hard drive, and installing grub to the hard drive (if it isn't already there) and adding the appropriate grub.cfg lines to point to the iso on the HD and install from there, though a separate live usb or cd is more common and should be more tested & reliable... And if you want to overwrite your whole HD, including the iso you booted from, and have enough ram you could boot the live iso with the toram boot parameter (added to the line with noeject noprompt splash toram -- for example)