This chapter contains a brief overview of the build process and instructions for using the three most commonly used image types. The most versatile image type, iso-hybrid, may be used on a virtual machine, optical media or USB portable storage device. In certain special cases, such as the use of persistence, usb-hdd may be more suitable for USB devices. The chapter finishes with instructions for building and using a net type image, which is a bit more involved due to the setup required on the server. This is a slightly advanced topic for anyone who is not familiar already with netbooting, but is included here because once the setup is done, it is a very convenient way to test and deploy images for booting on the local network without the hassle of dealing with image media.
Throughout the chapter, we will often refer to the default filenames produced by live-build. If you are downloading a prebuilt image instead, the actual filenames may vary.
A live system usually means an operating system booted on a computer from a removable medium, such as a CD-ROM or USB stick, or from a network, ready to use without any installation on the usual drive(s), with auto-configuration done at run time (see Terms).
With Debian Live, it's a Debian GNU/Linux operating system, built for one of the supported architectures (currently amd64, i386, powerpc and sparc). It is made from the following parts:
You can use live-build to build the system image from your specifications, set up a Linux kernel, its initrd, and a bootloader to run them, all in one media-dependant format (ISO9660 image, disk image, etc.).
Regardless of the image type, you will need to perform the same basic steps to build an image each time. As a first example, execute the following sequence of live-build commands to create a basic ISO hybrid image containing just the Debian standard system without X.org. It is suitable for burning to CD or DVD media, and also to copy onto a USB stick.
First, run the lb config command. This will create a "config/" hierarchy in the current directory for use by other commands:
$ lb config
No parameters are passed to lb config, so defaults for all of its various options will be used. See The lb config command for more details.
Now that the "config/" hierarchy exists, build the image with the lb build command:
# lb build
This process can take a while, depending on the speed of your network connection. When it is complete, there should be a binary-hybrid.iso image file, ready to use, in the current directory.
After either building or downloading an ISO hybrid image, which can be obtained at ‹http://www.debian.org/CD/live/›, the usual next step is to prepare your media for booting, either CD-R(W) or DVD-R(W) optical media or a USB stick.
Burning an ISO image is easy. Just install wodim and use it from the command-line to burn the image. For instance:
# apt-get install wodim
$ wodim binary-hybrid.iso
ISO images prepared with the isohybrid command, like the images produced by the default iso-hybrid binary image type, can be simply copied to a USB stick with the dd program or an equivalent. Plug in a USB stick with a size large enough for your image file and determine which device it is, which we hereafter refer to as ${USBSTICK}. This is the device file of your key, such as /dev/sdb, not a partition, such as /dev/sdb1! You can find the right device name by looking in dmesg's output after plugging in the stick, or better yet, ls -l /dev/disk/by-id.
Once you are certain you have the correct device name, use the dd command to copy the image to the stick. This will definitely overwrite any previous contents on your stick!
$ dd if=binary-hybrid.iso of=${USBSTICK}
The first time you boot your live media, whether CD, DVD, USB key, or PXE boot, some setup in your computer's BIOS may be needed first. Since BIOSes vary greatly in features and key bindings, we cannot get into the topic in depth here. Some BIOSes provide a key to bring up a menu of boot devices at boot time, which is the easiest way if it is available on your system. Otherwise, you need to enter the BIOS configuration menu and change the boot order to place the boot device for the live system before your normal boot device.
Once you've booted the media, you are presented with a boot menu. If you just press enter here, the system will boot using the default entry, Live and default options. For more information about boot options, see the "help" entry in the menu and also the live-boot and live-config man pages found within the live system.
Assuming you've selected Live and booted a default desktop live image, after the boot messages scroll by, you should be automatically logged into the user account and see a desktop, ready to use. If you've booted a console-only image, such as standard or rescue flavour prebuilt images, you should be automatically logged in on the console to the user account and see a shell prompt, ready to use.
It can be a great time-saver for the development of live images to run them in a virtual machine (VM). This is not without its caveats:
Provided you can work within these constraints, survey the available VM software and choose one that is suitable for your needs.
The most versatile VM in Debian is QEMU. If your processor has hardware support for virtualization, use the qemu-kvm package; the qemu-kvm package description briefly lists the requirements.
First, install qemu-kvm if your processor supports it. If not, install qemu, in which case the program name is qemu instead of kvm in the following examples. The qemu-utils package is also valuable for creating virtual disk images with qemu-img.
# apt-get install qemu-kvm qemu-utils
Booting an ISO image is simple:
$ kvm -cdrom binary-hybrid.iso
See the man pages for more details.
In order to test the ISO with virtualbox-ose:
# apt-get install virtualbox-ose virtualbox-ose-dkms
$ virtualbox
Create a new virtual machine, change the storage settings to use binary-hybrid.iso as the CD/DVD device, and start the machine.
Note: For live systems containing X.org that you want to test with virtualbox-ose, you may wish to include the VirtualBox X.org driver package, virtualbox-ose-guest-x11, in your live-build configuration. Otherwise, the resolution is limited to 800x600.
$ lb config --packages virtualbox-ose-guest-x11
Building a USB/HDD image is similar to ISO hybrid in all respects except you specify -b usb-hdd and the resulting filename is binary.img which cannot be burnt to optical media. It is suitable for booting from USB sticks, USB hard drives, and various other portable storage devices. Normally, an ISO hybrid image can be used for this purpose instead, but if you have a BIOS which does not handle hybrid images properly, or want to use the remaining space on the media for some purpose, such as a persistence partition, you need a USB/HDD image.
Note: if you created an ISO hybrid image with the previous example, you will need to clean up your working directory with the lb clean command (see The lb clean command):
# lb clean --binary
Run the lb config command as before, except this time specifying the USB/HDD image type:
$ lb config -b usb-hdd
Now build the image with the lb build command:
# lb build
When the build finishes, a binary.img file should be present in the current directory.
The generated binary image contains a VFAT partition and the syslinux bootloader, ready to be directly written on a USB stick. Since using a USB/HDD image is just like using an ISO hybrid image on USB, follow the instructions in Using an ISO hybrid live image, except use the filename binary.img instead of binary-hybrid.iso.
First, install QEMU as described above in Testing an ISO image with QEMU. Then run kvm or qemu, depending on which version your host system needs, specifying binary.img as the first hard drive.
$ kvm -hda binary.img
To use the remaining free space after copying binary.img to a USB stick, use a partitioning tool such as gparted or parted to create a new partition on the stick. The first partition will be used by the Debian Live system.
# gparted ${USBSTICK}
After the partition is created, where ${PARTITION} is the name of the partition, such as /dev/sdb2, you have to create a filesystem on it. One possible choice would be ext4.
# mkfs.ext4 ${PARTITION}
Note: If you want to use the extra space with Windows, apparently that OS cannot normally access any partitions but the first. Some solutions to this problem have been discussed on our mailing list, but it seems there are no easy answers.
Remember: Every time you install a new binary.img on the stick, all data on the stick will be lost because the partition table is overwritten by the contents of the image, so back up your extra partition first to restore again after updating the live image.
The following sequence of commands will create a basic netboot image containing the Debian standard system without X.org. It is suitable for booting over the network.
Note: if you performed any previous examples, you will need to clean up your working directory with the lb clean command:
# lb clean --binary
Run the lb config command as follows to configure your image for netbooting:
$ lb config -b net --net-root-path "/srv/debian-live" --net-root-server "192.168.0.1"
In contrast with the ISO and USB/HDD images, netbooting does not, itself, serve the filesystem image to the client, so the files must be served via NFS. The --net-root-path and --net-root-server options specify the location and server, respectively, of the NFS server where the filesytem image will be located at boot time. Make sure these are set to suitable values for your network and server.
Now build the image with the lb build command:
# lb build
In a network boot, the client runs a small piece of software which usually resides on the EPROM of the Ethernet card. This program sends a DHCP request to get an IP address and information about what to do next. Typically, the next step is getting a higher level bootloader via the TFTP protocol. That could be pxelinux, GRUB, or even boot directly to an operating system like Linux.
For example, if you unpack the generated binary-net.tar.gz archive in the /srv/debian-live directory, you'll find the filesystem image in live/filesystem.squashfs and the kernel, initrd and pxelinux bootloader in tftpboot/debian-live/i386.
We must now configure three services on the server to enable netboot: the DHCP server, the TFTP server and the NFS server.
We must configure our network's DHCP server to be sure to give an IP address to the netbooting client system, and to advertise the location of the PXE bootloader.
Here is an example for inspiration, written for the ISC DHCP server isc-dhcp-server in the /etc/dhcp/dhcpd.conf configuration file:
# /etc/dhcp/dhcpd.conf - configuration file for isc-dhcp-server
ddns-update-style none;
option domain-name "example.org";
option domain-name-servers ns1.example.org, ns2.example.org;
default-lease-time 600;
max-lease-time 7200;
log-facility local7;
subnet 192.168.0.0 netmask 255.255.255.0 {
range 192.168.0.1 192.168.0.254;
next-server servername;
filename "pxelinux.0";
}
This serves the kernel and initial ramdisk to the system at run time.
You should install the tftpd-hpa package. It can serve all files contained inside a root directory, usually /srv/tftp. To let it serve files inside /srv/debian-live/tftpboot, run as root the following command:
# dpkg-reconfigure -plow tftpd-hpa
and fill in the new tftp server directory when being asked about it.
Once the guest computer has downloaded and booted a Linux kernel and loaded its initrd, it will try to mount the Live filesystem image through a NFS server.
You need to install the nfs-kernel-server package.
Then, make the filesystem image available through NFS by adding a line like the following to /etc/exports:
/srv/debian-live *(ro,async,no_root_squash,no_subtree_check)
and tell the NFS server about this new export with the following command:
# exportfs -rv
Setting up these three services can be a little tricky. You might need some patience to get all of them working together. For more information, see the syslinux wiki at ‹http://syslinux.zytor.com/wiki/index.php/PXELINUX› or the Debian Installer Manual's TFTP Net Booting section at ‹http://d-i.alioth.debian.org/manual/en.i386/ch04s05.html›. They might help, as their processes are very similar.
Netboot image creation is made easy with live-build magic, but testing the images on physical machines can be really time consuming.
To make our life easier, we can use virtualization. There are two solutions.
Edit /etc/qemu-ifup:
#!/bin/sh
sudo -p "Password for $0:" /sbin/ifconfig $1 172.20.0.1
echo "Executing /etc/qemu-ifup"
echo "Bringing up $1 for bridged mode..."
sudo /sbin/ifconfig $1 0.0.0.0 promisc up
echo "Adding $1 to br0..."
sudo /usr/sbin/brctl addif br0 $1
sleep 2
Get, or build a grub-floppy-netboot (in the svn).
Launch qemu with "-net nic,vlan=0 -net tap,vlan=0,ifname=tun0"
#!/usr/bin/vmware
config.version = "8"
virtualHW.version = "4"
memsize = "512"
MemAllowAutoScaleDown = "FALSE"
ide0:0.present = "FALSE"
ide1:0.present = "FALSE"
floppy0.present = "FALSE"
sound.present = "FALSE"
tools.remindInstall = "FALSE"
ethernet0.present = "TRUE"
ethernet0.addressType = "generated"
displayName = "Test Boot PXE"
guestOS = "other"
ethernet0.generatedAddress = "00:0c:29:8d:71:3b"
uuid.location = "56 4d 83 72 5c c4 de 3f-ae 9e 07 91 1d 8d 71 3b"
uuid.bios = "56 4d 83 72 5c c4 de 3f-ae 9e 07 91 1d 8d 71 3b"
ethernet0.generatedAddressOffset = "0"