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The Fedora live CD tools David Zeuthen <firstname.lastname@example.org> Jeremy Katz <email@example.com> Last updated: March 10, 2014 (v20.5) This project concerns tools to generate live CD's on Fedora based systems including derived distributions such as RHEL, CentOS and others. See the project Wiki at http://fedoraproject.org/wiki/FedoraLiveCD for more details. Discussion of this project takes places at the firstname.lastname@example.org mailing list http://www.redhat.com/mailman/listinfo/fedora-livecd-list This project and it's source files is licensed under the GPLv2 license. See the file COPYING for details. 1. LIVE CD DESIGN GOALS The live CD is designed in such a way that the when running from a live CD, the system should appear as much as possible as a standard system with all that entails; e.g. read-write rootfs (achieved using dm-snapshot), standard ext3 file system (for extended attributes) and so on. Another design goal is that the live CD should be ''installable'', ie. an user should be able to install the bits from the live CD onto his hard disk without this process requiring network access or additional media. Finally, another design goal is that the tool set itself should be separate from configuration; the same unmodified tool should be usable for building various live CD flavors with vastly different configurations, e.g. a GNOME live CD, a KDE live CD, a live cd with music programs and so on. 2. CREATING A LIVE CD To create a live cd, the livecd-creator tool is used. Super user privileges are needed. The tool is more or less self-documenting, use the --help option to see options. 2.1 HOW THE LIVE CD CREATOR WORKS In a nutshell, the livecd-creator program o Sets up a file for the ext3 file system that will contain all the data comprising the live CD o Loopback mounts that file into the file system so there is an installation root o Bind mounts certain kernel file systems (/dev, /dev/pts, /proc, /sys, /selinux) inside the installation root o Uses a configuration file to define the requested packages and default configuration options. The format of this file is the same as is used for installing a system via kickstart. o Installs, using yum, the requested packages into the installation using the given repositories o Optionally runs scripts as specified by the live CD configuration file. o Relabels the entire installation root (for SELinux) o Creates a live CD specific initramfs that matches the installed kernel o Unmounts the kernel file systems mounted inside the installation root o Unmounts the installation root o Runs resize2fs to minimize and unminimize the ext3 file to remove data from deleted files o Runs resize2fs to minimize on a devicemapper snapshot, to generate a small minimized delta image file which can be used by anaconda to reduce installation time by not copying unused data to disk o Creates a squashfs file system containing only the ext3 file (compression) o Configures the boot loader o Creates an iso9660 bootable CD 2.2 EXAMPLE: A BAREBONES LIVE CD The command # livecd-creator \ --config=/usr/share/doc/livecd-tools/livecd-fedora-minimal.ks will create a live CD that will boot to a login prompt. Note that since no configuration is done the user will not be able to login to the system as the root password is not set / cleared. 2.3 LIVE CD CONFIGURATION FILES The configuration of the live CD is defined by a file that uses the same format as installing a system via kickstart. They can include some basic system configuration items, the package manifest and a script to be run at the end of the build process. For the Fedora project, there are currently a variety of different live CD configuration files. The spin-kickstarts package includes all of the kickstarts used to create the various spins. These include a minimal live image (livecd-fedora-minimal.ks), a complete desktop image (livecd-fedora-desktop.ks) and others. 2.4 EXAMPLE: SPINNING THE FEDORA DESKTOP LIVE CD Assuming that you use the livecd-fedora-desktop.ks configuration file, then the following command # livecd-creator \ --config=/usr/share/spin-kickstarts/fedora-livecd-desktop.ks \ --fslabel=Fedora-20-LiveCD-1-foo will create a live CD called "Fedora-7-LiveCD-1-foo". The name given by --fslabel is used. o as a file system label on the ext3 and iso960 file systems (as such it's visible on the desktop as the CD name) o in the isolinux boot loader If you have the repositories available locally and don't want to wait for the download of packages, just substitute the URLs listed in the configuration file to point to your local repositories. 3. LIVE CD INSTALLS As of Fedora 7, anaconda has support for doing an installation from a live CD. To use this, double click on the "Install to Hard Drive" item on the desktop or run /usr/bin/liveinst if you don't have such an icon. 4. LIVE CD MEDIA VERIFICATION The live CD can incorporate functionality to verify itself. To do so, you need to have anaconda-runtime installed both on the system used for creating the image and installed into the image. This is so that the implantisomd5 and checkisomd5 utilities can be used. These utilities take advantage of embedding an md5sum into the application area of the iso9660 image. This then gets verified before mounting the real root filesystem. In a future release, the isomd5 utilities will probably be split out of anaconda. 5. USING LIVE IMAGES FROM USB MEDIA USB sticks are becoming increasingly prevalent and are a nice way to use live images. You can take a live CD iso image and transform it so that it can be used on a USB stick. To do so, use the livecd-iso-to-disk script. /usr/bin/livecd-iso-to-disk /path/to/live.iso /dev/sdb1 Replace /dev/sdb1 with the (unmounted) partition where you wish to put the live image. This is not a destructive process; any data you currently have on your USB stick will be preserved.