Boot and Dual Boot From a USB Thumb Drive

If you've ever thought about dual booting (see a lot more here) you've probably discovered some confusing choices. By dual booting you can have two (or several) operating systems available on the same computer. When the computer boots you'll get a menu with choices for which OS to boot, a very handy capability.
You can also have virtual machines that are instances of operating systems running within another operating systems. If you dual boot, each OS is completely independent of the other; they can't both be active at the same time. A virtual machine can run one or more operating systems at the same time (see an example here which has advantages of course.

If you have the disk space and enough memory, you can both dual boot and run virtual machines to take full advantage of your hardware and provide the most possible power and convenience. There's still another major advantage of a dual boot configuration; creating a portable operating system you can use to manage and restore another computer.

USB thumbs drives have enough storage capacity for at least one operating system and all the utilities you might need to troubleshoot problems on other computers. Since the USB thumb drive simply plugs into a USB (version 2 of course) port and most computers have these ports, a USB thumb drive with a bootable OS can be used to boot any computer.

The only preparation is to set the boot drive order in the BIOS to try the USB thumb drive first and then the computer's hard disk second. Set that correctly, insert the USB thumb drive and boot up. The machine will boot from the thumb drive and load whatever OS you installed on it.

If your computer supports booting from a USB thumb drive (and most do), all you really have to do is insert a Linux install CD/DVD, boot and, when prompted for you partitioning scheme, chose "Custom", select the thumb drive (probably the second disk) as the installation target and configure the grub bootloader (see more detail here) to display thumb drive as a boot choice.

Now when you re-boot, you'll see the thumb drive in the grub menu list of operating systems it can boot. Select the thumb drive, hit Enter and grub will boot to the USB thumb drive just like any other disk-based operating system. Everything you selected during the installation process (see more on this here) will be available and fully functional. You now have a portable Linux installation you can plug into the USB port of any computer and boot into. This makes any computer able to dual boot by just inserting the thumb drive.

Very handy stuff. There are other reasons for doing this, however. Suppose you have a problem with the operating system on another computer, do you format and re-install the OS, losing everything? No way. If you've included some useful and powerful utilities in your thumb drive installation, you can boot from the thumb drive on the broken computer and use those utilities to fix it. There's even a boot image you can get that's especially configured for this, here.

If you need to fix a broken Linux installation, you need to have Linux installed on the thumb drive as mentioned above. Suppose your Linux configured on the hard disk is so corrupted that the only solution is to re-install? You always be prepared for the worst, especially if you're getting paid to manage someone else's servers. Think of it as disaster avoidance.

Any time you install Redhat or Fedora, the installation will create a "kickstart" or "anaconda-ks.cfg" file the /root directory (for much more detail, see this). This file has everything you selected to install in the original setup. Copy that file to another disk on, ideally, another machine and give it a name identifying it. Call the webserver kickstart file something like webserver.kickstart. That file is then made available for any subsequent installation making it pretty much automatic. If you're configuring a thumb drive for server recovery, copy the kickstart file there.

While using kickstart is hugely convenient, it doesn't help with stuff you added after the initial operating system installation. During the installation of Linux to your computer, you need to carefully plan how your disk partitions are set up (see a detailed explanation, here).

When you re-install over an existing installation you really only need to install the operating system specific stuff, everything else can be left as is. To prevent catastrophic loss of data or capability and get the machine back on-line as fast as possible, you should divide the original installation over several partitions. These should be:


and possibly,


During the installation you only have to format the partitions that are required to fix the problems. These are usually, /boot, /, /usr and, probably, /var. If the broken machine was a mail server, you might want to create a separate partition for /var/mail (the default for Redhat and Fedora) so you don't overwrite your user's mail during the install. Since /home and /usr/local have most of the customized stuff and user installed programs, they're the ones you really want to preserve. Because they are on their own partitions they don't have to be formatted and they are preserved, untouched by the installation.

Let's assume that prior to the OS corruption we're trying to correct, you had everything working and properly configured. All of this took time and lots of effort so restoring those configurations will likewise be time consuming. Since we're wanting to get this machine back on-line as soon as possible, we can't be messing around trying to figure out how to get everything back.

Once you've gotten a server alive and everything configured, you need to document everything and the best way to do that is with a shell script. This script will not only tell us what we've done but also how to put everything back like was. Here's an example:

echo -ne "

* Run as root *

This script is to create a working environment
after a new install to boot from a thumb drive.

This will copy stuff after a new install
and put it in the right places. Some services
will have to restart but a reboot is better.

* Run as root *

Hit Enter to begin ... \c"
read "ans"

# put the thunderbird mail client back
if [ ! -d /usr/local/thunderbird ]
mkdir /usr/local/thunderbird
ln -s /media/usr/local/thunderbird/thunderbird /usr/local/thunderbird

# Notice that a symbolic link is used since we assume that the /media
# filesystem is permantently mounted. If it isn't you need to copy
# it over so try using something like:

# cd /media/usr/local/thunderbird
# find . -depth|cpio -pdv /usr/local/thunderbird

# put the firefox web browser back
if [ ! -d /usr/local/firefox ]
mkdir /usr/local/firefox
ln -s /media/usr/local/firefox/firefox /usr/local/firefox

# Add Apache in case I want a local webserver
ln -s /media/usr/local/apache2 /usr/local/apache2

# Get the Broadcom wireless driver restored
if [ ! -d /lib/firmware/b43 ]
mkdir /lib/firmware/b43
cp ../wl_apsta- /lib/firmware/b43
cp ../b43/* /lib/firmware/b43
cp ../wl_apsta- /lib/firmware

# Update /etc
cp httpd /etc/rc.d/init.d
cp wicd /etc/rc.d/init.d
cp ifcfg-wlan0 /etc/sysconfig/network-scripts
cp ifup-wireless /etc/sysconfig/network-scripts
cp keys-wlan0 /etc/sysconfig/network-scripts
cp route-wlan0 /etc/sysconfig/network-scripts
cp hosts /etc
cp passwd /etc
cp resolv.conf /etc
cp shadow /etc
cp modprobe.conf /etc
cp selinux_config /etc/selinux/config

# Disable the Synaptics Touchpad:
cp xorg.conf /etc/X11

# Not needed on Fedora 9 installation but
# since the default install puts an underscore (_)
# in front of directory names mounted in /media
# and I find that annoying, mkdir without the
# underscore and mount to them instead.

# cp fstab /etc

# Restore the wicd wireless configuration going
if [ ! -d /etc/wicd ]
mkdir /etc/wicd

cd wicd-conf
find . -depth|cpio -pdv /etc/wicd
cd ..

if [ ! -d /etc/wpa_supplicant ]
mkdir /etc/wpa_supplicant
cp wpa_supplicant.conf /etc/wpa_supplicant

# make sure only the service I want are restored
chkconfig NetworkManager off
chkconfig bluetooth off
chkconfig cups off
chkconfig dnsmasq off
chkconfig ip6tables off
chkconfig nfs off
chkconfig nfslock off
chkconfig restorecond off
chkconfig sendmail off
chkconfig setroubleshoot off
chkconfig network on

# use wicd for networking:
if [ `chkconfig --list|grep wicd` = "" ]
chkconfig --add wicd

# Re-install wicd for wireless
cd wicd-install
python configure && python install
cd ..

chkconfig wicd on

# Restore my environment
cp .bash_profile $HOME
cp .bashrc $HOME
cp .exrc $HOME

# make some stuff available in my $HOME directory
cp wlan-config-3.4.tar.bz2 $HOME
cp wl_apsta- $HOME
cp b43-fwcutter-011.tar.bz2 $HOME
cp broadcom-wl- $HOME
cp NetworkManager-0.7.0.tar.gz $HOME
cp ntfs-3g-2009.1.1.tgz $HOME

# Load the Broadcom driver
modprobe b43

# More wireless stuff
if [ ! -d $HOME/wireless ]
mkdir $HOME/wireless
cd wireless
find . -depth|cpio -pdv $HOME/wireless

# Restore my firefox configuration
if [ ! -d $HOME/.mozilla ]
find ../.mozilla -depth|grep -v Cache|cpio -pdv $HOME/.mozilla

Restore my email configuration
if [ ! -d $HOME/.thunderbird ]
mkdir $HOME/.thunderbird
find ../.thunderbird -depth|grep -v Cache|cpio -pdv $HOME/.thunderbird

# Enable the wireless interface
ifup wlan0
# Enable networking
service network restart
# Try wicd
service wicd start # Restore all the user configurations and environments
find /media_1/home -depth|cpio -pdv /home

Think of this script as a template. You'll have different requirements, but this should suggest how to get everything back up as fast as possible. Notice that I copied the server configuration files here ($HOME/etc). Below is a list of what's in this directory and why:
b43 This directory has all the driver files for a Broadcom wireless NIC
copy-new This is script that puts everything back like it was
fstab This saves the original file system layout
group Restores the original /etc/group file
hosts Restores the original /etc/hosts file
httpd Restores the original Apache server
ifcfg-wlan0 Restores the wireless card configuration
ifup-wireless Restores the wireless setup
keys-wlan0 Preserves the wireless WPA key
modprobe.conf Restores the Broadcom driver
passwd Restores the original /etc/passwd file
resolv.conf Restores the original /etc/resolv.conf for nameservers
route-wlan0 Restores routes for wireless network
selinux_config Restores the selinux configuration
shadow Restores the original /etc/shadow file
wicd This directory has all is for the wicd wireless driver
wicd-conf The wicd wireless configuration file
wicd-install This directory has the python installation scripts to re-install wicd
wl_apsta-3 Another Broadcom driver file
wpa_supplicant This directory is for the wpa_supplicant configuration
wpa_supplicant.conf This is the wpa_supplicant configuration files for wireless
xorg.conf Restores the /etc/X11/xorg.conf file
Obviously the first time you set all this up it will be tedious and error prone, but something like this is a real life saver (could save your job too). Remember that all this is on the USB thumb drive you booted from so you can plug the thumb drive into any computer, boot, run the restore script and get the broken system back to life quickly.

Consider that a USB thumb drive can have fairly huge capacity compared to a CD or DVD so it's by far the best choice for this kind of thing. You can either have different scripts for different servers or separate thumb drives for each server. Since all the restoration work was done and tested prior to a computer problem requiring a re-installation of the OS, full recovery can be accomplished quickly, probably less than two hours.

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