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<h1><span><em>live Arch Linux</em> builder</span></h1>
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<div class="indent1">Building the live system</div></a></li>
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<h2 id="pagetitle" level="1">Preparing the <em>larch live</em> medium</h2>
<p>The building blocks for the preparation of a <em>live</em> medium are
produced by the 'larchification' process: the <em>squashfs</em>
archive, 'system.sqf', the 'boot' directory, containing the kernel and
<em>initramfs</em>, and the modifications overlay, 'mods.sqf'.
</p>
<p>This stage adds the bootloader files and user-defined customisations
which are directly copied to the medium rather than being included in
the overlay (essentially the stuff from the 'cd-root' directory in the
profile. See the <a href="profiles.html#cd-root">cd-root</a> section in the
profiles documentation for details on how to customise this data. On
writeable media it is also possible to specify that the medium be used
as a writeable overlay branch in the <em>aufs</em> root ('/') file-system.
Finally the system is written to
the medium, if it is a partition (USB-stick, etc.), or - in the case
of a CD/DVD - an <em>iso</em> file is created.
</p>
<p>The structure of the <em>live</em> system is such that it is fairly
easy to transfer a <em>larch</em> system from one medium to another,
including the preservation of changes that have been made using the
data persistence facility, and including the possibility of transferring
a non-writeable system to a writeable medium and then enabling data
persistence. Support files for these operations are saved in the
'/boot/support' directory of the medium - these are mostly binary executables
which may not be available (in the correct version) on the machine used
to perform the operations. The libraries they need are also included, and the
applications must be run as
</p>
<pre> path/to/support/support application-name arguments</pre>
<p>The applications supported in this way are <em>mksquashfs</em>, <em>unsquashfs</em>,
<em>extlinux</em> and <em>syslinux</em>.
Also the binaries 'mbr.bin' and 'isolinux.bin' from the <em>syslinux</em>
package are made available here. The copying process can, however, be delegated to
the 'larch-medium' script, the source medium being specified using the '-S'
option (run 'larch-medium -h' for all options).
</p>
<h3><a name="overlay_persist"></a>Data Persistence: The Writeable Overlay</h3>
<p>The medium (partition) containing the <em>larch</em> system can be used
as a writeable overlay branch for the <em>live</em> system (assuming the
partition actually is writeable), causing changes made while running the
system to be preserved from one boot to the next, basically the same as
in a 'normal' linux system. The advantage this has over just installing a
normal linux system on the partition is that the bulk of the underlying
system is highly compressed, allowing smaller devices to be used than would
otherwise be possible. It is also relatively straightforward to transfer
such a system to and from non-writeable media, such as CD/DVD.
</p>
<p>If the medium is not writeable (or if the 'nw' boot parameter is passed)
then a writeable layer is created in <em>tmpfs</em>, a memory based file-system,
allowing the system to act 'normally' (i.e. the file-system appears
writeable) while running. However any changes will be lost on shutdown.
There are situations (e.g. 'kiosk'-systems) where this behaviour can even
be an advantage.
</p>
<h3><a name="media_scripts"></a>Command-line Scripts</h3>
<p>The command line script for building a <em>larch live</em> is
<strong>larch-medium</strong>. Run 'larch-medium -h' to get a
usage message.
</p>
<p>When the <em>live</em> system is installed to a partition (e.g.
USB-stick) it is possible to choose how the boot partition will be
recognized.
The options available are via UUID, partition label, partition path
(e.g. '/dev/sdb1'), or by searching for a partition
containing the file 'larch/larchboot'. See also
<a href="larch_running.html#bootparm">'Boot parameters'</a>.
</p>
<p>The 'bootlines' file allows the boot options to be specified in an
easily parseable, bootloader independent way. The default version
is supplied in the 'larch' package (in the 'cd-root/boot0' directory),
but this will be overridden by a version supplied in the profile.
The unprocessed version is also retained in the 'boot' directory of
the created medium, for later reference.
</p>
<p>It is possible to repeat the installation onto various media, changing
the configuration, without needing to rerun the 'larchification' stage.
The constituent <em>larch</em> files remain unchanged.
</p>
<h3><a name="usb2bootiso"></a>Building a boot CD for a USB-stick</h3>
<p>Older computers may not be able to boot from USB devices, so the
possibility of generating a small <em>boot iso</em> is provided. This can
be burned to CD and can be used to boot your <em>larch</em> system on a
USB-stick. On the command line this is managed by passing the '-b' option
to the <strong>larch-medium</strong> script.
As this function uses the system on the USB-stick, this needs to be
plugged in (not mounted!) and selected in the 'Partition' entry.
</p>
<p>As the kernel and <em>initramfs</em> are now taken from the CD rather
than from the USB device, an update of the kernel on the actual <em>larch</em>
medium would require the creation of a new boot-CD.
</p>
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