Gentoo Linux LiveUSB HOWTO

1.6 2006-09-18 Introduction

The LiveUSB

This HOWTO explains how to create a Gentoo Linux LiveUSB or, in other words, how to emulate a Gentoo Linux Installation CD using an USB flash drive. This is particularly useful for installing Gentoo Linux on a modern laptop with no CD-ROM drive.

Although the instructions found in this document aim at emulating a Gentoo Linux Installation CD using an USB flash drive, they should work for any arbitrary block device as long as you adjust the device names accordingly.

Prerequisites

In order to use a Gentoo Linux LiveUSB you need the following:

Bootable USB flash drive (at least 64MB)
x86 computer with support for booting from USB

You will also need access to the following for creating the LiveUSB:

A computer running Gentoo Linux (or alternatively another Linux distribution)

Preparing the USB flash drive

Partitioning the drive These instructions will erase all data from the USB flash drive. Make sure to backup your data first. This HOWTO assumes that the /dev/sda device node corresponds to your USB flash drive. If you have other SCSI-like devices make sure to use the correct device node.

Create a FAT32 partition on your USB flash drive and mark it bootable using fdisk. An example partitioning scheme can be seen below:

# fdisk -l /dev/sda

Disk /dev/sda: 1048 MB, 1048313856 bytes
33 heads, 61 sectors/track, 1017 cylinders
Units = cylinders of 2013 * 512 = 1030656 bytes

   Device Boot      Start         End      Blocks   Id  System
/dev/sda1   *           1        1017     1023580    b  W95 FAT32

Creating the filesystem

Create a FAT32 filesystem on the USB flash drive using mkdosfs:

(Make sure you have sys-fs/dosfstools installed)
# emerge -av sys-fs/dosfstools
# mkdosfs -F 32 /dev/sda1
mkdosfs 2.11 (12 Mar 2005)

Installing a Master Boot Record

Install the precompiled Master Boot Record (MBR) from syslinux on the USB flash drive:

(Make sure you have sys-boot/syslinux-3.00 or later installed)
# emerge -av '>=sys-boot/syslinux-3*'
# dd if=/usr/lib/syslinux/mbr.bin of=/dev/sda
0+1 records in
0+1 records out

Copying the files

Mounting the Gentoo Linux Installation CD This guide is designed only to be used with Gentoo 2006.0. Do not attempt to use a 2006.1 CD or newer; you will end up with an unbootable USB disk.

Download the install-x86-minimal-2006.0.iso file from your local Gentoo Linux mirror site and mount the ISO image on /mnt/cdrom/ as shown below:

(Create the /mnt/cdrom/ mount point if needed)
# mkdir -p /mnt/cdrom
# mount -o loop,ro -t iso9660 install-x86-minimal-2006.0.iso /mnt/cdrom/

If you receive a Could not find any loop device error message when mounting the iso, you need to enable the Loopback device support option in your kernel configuration.

Mounting the LiveUSB

Mount the newly formatted USB flash drive on /mnt/usb/ as shown below:

(Create the /mnt/usb/ mount point if needed)
# mkdir -p /mnt/usb
# mount -t vfat /dev/sda1 /mnt/usb/

Copying the files

Copy the files from the Gentoo Linux Installation CD to the LiveUSB. The files need to be reordered a bit as we will be using the syslinux bootloader instead of isolinux:

# cp -r /mnt/cdrom/* /mnt/usb/
# mv /mnt/usb/isolinux/* /mnt/usb/
# mv /mnt/usb/isolinux.cfg /mnt/usb/syslinux.cfg
# rm -rf /mnt/usb/isolinux*

(The memtest86 kernel needs to be renamed for loading it via syslinux)
# mv /mnt/usb/memtest86 /mnt/usb/memtest

You can now unmount the ISO image:

# umount /mnt/cdrom/

Adjusting the bootloader configuration

Adjust the syslinux configuration file using sed as shown below. The dobladecenter parameter will introduce some extra delays before attempting to mount the filesystem. This is needed to allow the USB flash drive to settle upon detection.

# sed -i \
    -e "s:cdroot:cdroot dobladecenter:" \
    -e "s:kernel memtest86:kernel memtest:" \
    /mnt/usb/syslinux.cfg

Consider adding docache to the boot parameters. This will allow running umount /mnt/cdrom/ after booting so that you can unplug the USB flash drive. Do not enable this unless the target computer has at least 128MB RAM.

Installing a bootloader

Unmounting the drive

Make sure you unmount the USB flash drive before installing the bootloader:

# umount /mnt/usb/

Installing syslinux

Finally install the syslinux bootloader on the USB flash drive:

# syslinux /dev/sda1

You will need to rerun syslinux /dev/sda1 each time you modify the syslinux.cfg file for the configuration changes to take affect.

Using the LiveUSB

Booting

Insert the USB flash drive and turn on the computer, making sure the BIOS is set to boot from USB. If all goes well you should be presented with a standard syslinux prompt.

You should be able to follow the generic installation instructions found in the Gentoo Handbook from here on.