For preparing the USB stick you will need a system where GNU/Linux is
already running and where USB is supported. You should ensure that the
usb-storage kernel module is loaded (modprobe
usb-storage) and try to find out which SCSI device the USB
stick has been mapped to (in this example
/dev/sda is used). To write to your stick, you
will probably have to turn off its write protection switch.
Note that the USB stick should be at least 8 MB in size. If you follow Section 4.3.2, “Copying the files — the flexible way” and want to include an Ubuntu ISO image on the stick, you will need enough space for the ISO as well.
There is an all-in-one file netboot/boot.img.gz which contains all the installer files (including the kernel) as well as SYSLINUX and its configuration file. You only have to extract it directly to a partition on your USB stick:
# zcat boot.img.gz > /dev/sda1
Of course this will destroy anything already on the device, so take care that you use the correct device name for your USB stick.
If you like more flexibility or just want to know what's going on, you should use the following method to put the files on your stick.
We will show how to setup the memory stick to use the first partition, instead of the entire device.
Since most USB sticks come pre-configured with a single FAT16 partition, you probably won't have to repartition or reformat the stick. If you have to do that anyway, use cfdisk or any other partitioning tool for creating a FAT16 partition and then create the filesystem using:
# mkdosfs /dev/sda1
Take care that you use the correct device name for your USB stick. The
mkdosfs command is contained in the
dosfstools Ubuntu package.
In order to start the kernel after booting from the USB stick, we will put a boot loader on the stick. Although any boot loader (e.g. LILO) should work, it's convenient to use SYSLINUX, since it uses a FAT16 partition and can be reconfigured by just editing a text file. Any operating system which supports the FAT file system can be used to make changes to the configuration of the boot loader.
To put SYSLINUX on the FAT16 partition on your USB
stick, install the syslinux and
mtools packages on your system, and do:
# syslinux /dev/sda1
Again, take care that you use the correct device name. The partition
must not be mounted when starting SYSLINUX. This
procedure writes a boot sector to the partition and creates the file
ldlinux.sys which contains the boot loader code.
Mount the partition (mount /dev/sda1 /mnt) and
copy the following files from the Ubuntu archives to the stick:
vmlinuz (kernel binary)
initrd.gz (initial ramdisk image)
syslinux.cfg (SYSLINUX configuration file)
Optional kernel modules
If you want to rename the files, please note that SYSLINUX can only process DOS (8.3) file names.
The syslinux.cfg configuration file should
contain the following two lines:
default vmlinuz append initrd=initrd.gz ramdisk_size=12000 root=/dev/rd/0 init=/linuxrc rw
Please note that the ramdisk_size parameter
may need to be increased, depending on the image you are booting.
If you are using the hd-media image, you should
now put any Ubuntu ISO image onto your stick (if it fits).
The file name of such an
image must end in .iso.
If you want to install over the network, without using an ISO image,
you will of course skip the previous step. Moreover you will have to
use the initial ramdisk from the netboot
directory instead of the one from hd-media,
because hd-media/initrd.gz does not have network
support.
When you are done, unmount the USB memory stick (umount
/mnt) and activate its write protection switch.