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<h1><span><em>live Arch Linux</em> builder</span></h1>
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<div class="indent1">Preparing the larch live medium</div></a></li>
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<h2 id="pagetitle" level="1">Building the <em>live</em> system</h2>
<p>Once we have an <em>Arch Linux</em> installation and have specified our
customizations in the profile, we can combine all this information into two
squashfs archives and an <em>initramfs</em> (to allow the <em>live</em> system
to boot). Let's call this step 'larchification' (from the verb 'larchify').
The lowest layer in the <em>aufs</em> mount is the raw installation,
which is compressed into a <em>squashfs</em> archive, 'system.sqf'.
All the modifications specified in the profile, as well, as some
common to all <em>larch</em> systems are in the archive 'mods.sqf', which
'overlays' the basic installation.
</p>
<p>For details of the structure of the <em>live</em> system which is built
by this stage see <a href="larch_live_system.html">this page</a>.
The bulk of the code in the <em>larchify</em> script is concerned with
building the 'mods.sqf' overlay, and a description of the main possibilities
for customizing the build process are covered in
<a href="profiles.html">the profiles documentation</a>.
</p>
<h3><a name="mkinitcpio"></a><em>mkinitcpio</em> and the <em>initramfs</em></h3>
<p>In order to build a suitable <em>initramfs</em> for a <em>larch</em>
system, a customized version of 'mkinitcpio.conf' is required. How
<em>larch</em> handles this is quite complicated because it aims to retain
the normal files so that the <em>live</em> system can later be installed
as a normal <em>Arch Linux</em> system, whilst at the same time offering
the capability of updating (with 'pacman -Syu') the <em>live</em> system,
including the kernel (thus requiring regeneration of the <em>initramfs</em>
for the system).
The consequence of this ambition is that modifications are made
within '/etc/mkinitcpio.d' (which are reversible when the <em>live</em>
system is installed as normal <em>Arch Linux</em> system) and a special
<em>mkinitcpio</em>' configuration file, '/etc/mkinitcpio.conf.larch'
is generated automatically (and thus should not be
touched by human hands!) from '/etc/mkinitcpio.conf.larch0'.
If you need to know more see the method 'Builder.gen_initramfs' in
'cli/larchify.py'.
</p>
<h3><a name="reuseSystem"></a>Rebuilding using an existing 'system.sqf'</h3>
<p>In order to aid experimentation with profile tweaks which do not affect
the underlying installation, it is possible to repeat the 'larchify' step
without rebuilding the 'system.sqf' archive, which saves quite a bit of time
(this is achieved by passing the '-o' option to 'larch-larchify' when running
from the command line).
</p>
<h3><a name="existingSystem"></a>Making a <em>live</em> system from an
existing <em>Arch</em> installation</h3>
<p>By setting the installation path (with the '-i' option if using the
command line) to an existing <em>Arch</em> installation,
a <em>live</em> medium can be made from it.
The installation must already be mounted, including any sub-mounts
(e.g. /home on another partition). The main mount must be with
options 'exec,dev', because most of the building is done via a <em>chroot</em>
to the installation. This approach to <em>live</em> system generation is
probably not a good idea if the installation contains a lot of data -
consider how big the result will be ...
</p>
<p>Also the currently running (<em>Arch</em> only!) system can be
<em>larchified</em>, by setting the installation path to '/'.
This is, however, not recommended. Building from a running system can easily
result in data corruption because the file-system might well change during
the build process.
</p>
<p>Note that some things in '/var' will not be included in the 'live' system.
Firstly, the standard <em>pacman</em> package cache ('/var/cache/pacman/pkg')
will be excluded.
Also the log files (in '/var/log') and '/var/tmp' (temporary files, like '/tmp')
are not saved. As some files in '/var/log' are required for certain aspects of
logging to function, these are recreated in the <em>initramfs</em>.
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