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diff --git a/build_tools/clarch/larch/docs/html/larch_sessionsave.html b/build_tools/clarch/larch/docs/html/larch_sessionsave.html new file mode 100644 index 0000000..edca50c --- /dev/null +++ b/build_tools/clarch/larch/docs/html/larch_sessionsave.html @@ -0,0 +1,162 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Transitional//EN" "http://www.w3.org/TR/xhtml1/DTD/xhtml1-transitional.dtd"> +<html> + +<head> + <meta content="text/html;charset=UTF-8" http-equiv="Content-Type" /> + <title>larch session saving</title> + <meta content="gradgrind" name="author" /> +</head> + +<body> + +<table style="text-align: left; width: 100%;" border="1" cellpadding="2" cellspacing="2"> + <tbody> + <tr> + <td><a href="larch_fstab.html">Previous: /etc/fstab</a></td> + + <td><a href="larch_docindex.html">Table of Contents</a></td> + + <td><a href="larch_ssh.html">Next: ssh access</a></td> + </tr> + </tbody> +</table> + +<br /> + +<h1><big>larch</big> – a do-it-yourself live <em>Arch Linux</em> CD</h1> + +<img style="border: 0px solid ; width: 320px; height: 320px;" alt="" src="larch1.jpg" + name="graphics1" align="right" hspace="10" vspace="10" /> +<br /><br /> + +<h2>Saving a session back to the boot device (or even somewhere else)</h2> + +<p>An easy way to create a customized live-USB-stick is to start from an +existing one, make whatever changes you like, and then save the result back to +the USB-stick. +</p> + +<h3><a name="overlays"></a>Overlay archives, <strong>overlay.ovl</strong> and +<strong>mods.sqf</strong></h3> + +<p>In <em>larch</em> the <em>overlay</em> file-system (in the +<em>compressed</em> file 'overlay.ovl') can be rebuilt +from the state of the live system when it shuts down. +This is handled primarily by the script <strong>/opt/larch-live/session-save/saveovl</strong>, which is +called from the customized shutdown function. +If the medium is writable and contains a file 'larch/save', the user is offered the possibility of +rewriting the overlay archive, thus saving the current state. +</p> + +<p>The main overlay archive (<strong>overlay.ovl</strong>) is unpacked into memory +at boot and repacked when saving the session at shutdown. When this archive grows +too large it will reduce the amount of available memory, perhaps to an unacceptable extent. +It will also lengthen boot and shutdown times. To counter this, it is possible to merge the +overlay archive into the middle <em>union</em> layer in <strong>mods.sqf</strong> (which is +normally not copied to memory), thus restoring the rapid load and save times +for <strong>overlay.ovl</strong>, and maximizing the available memory. I call this process +'overlay merging', and it is offered as a shutdown option. +It takes longer to execute than a normal session save, but from larch version 5.2 +a new <em>aufs</em> option allows the merging to be done quicker than it was +previously and without significant extra memory requirements. In this version +a separate <em>aufs</em> union of the two overlay layers is mounted in which +the whiteouts are visible. This union can then be squashed directly, without +requiring the new, merged overlay to be rebuilt in memory. As it is a feature +of <em>aufs</em>, overlay merging is no longer supported for <em>unionfs</em> +(note that <em>unionfs</em> is at present not actively supported in <em>larch</em> +anyway). +</p> + +<h3><a name="var_files"></a>Special places in /var</h3> + +<p>It was considered undesirable to include some things in the '/var' directory +in the session saves, primarily because of the space they occupy. Firstly, +the standard <em>pacman</em> package cache, '/var/cache/pacman/pkg' - if you +do want to save your cache, you should either handle this manually or set +up another location using 'CacheDir' in /etc/pacman.conf'. Also the log files +(in '/var/log') and '/var/tmp' (temporary files, like '/tmp') are not saved. +</p> + +<h3><a name="upd_packages"></a>Updating packages</h3> + +<p>It should be possible to include package addition and removal in the list +of customizations undertaken using this method, but there are some limitations. Apart from +size considerations (the top level overlay is unpacked into memory at boot), there is also +a limitation connected with the kernel. Essentially, the kernel and its modules may not +be updated. <strong>If you do this, you may well make a mess of your system</strong>. +In other words, be very careful with 'pacman -Su' - only upgrade selected packages. +</p> +<p>The reason for this is that the kernel is not contained within the +squashed file-system, but is held separately on the boot medium, while its modules +are contained in the squashed system and also in the initramfs. Updating these is not +impossible (if booting from a writable medium), but <em>pacman</em> cannot do it and +it is not straightforward (e.g. using a CD to boot to a USB-stick on a computer not +supporting USB boot would additionally need a new CD). A complete rebuild of the live +system might be a better approach. And using 'larchify' it should even be possible to +perform such a rebuild from within the running live system. +</p> + +<h3><a name="de-Act"></a>Activating and deactivating the session-saving feature</h3> + +<p>As mentioned above, for this feature to be available, there must be a file with +the name 'save' in the boot medium's 'larch' directory. +</p> + +<h3><a name="custom"></a>Customizing the behaviour using scripts</h3> + +<p>Some aspects of the session saving can be customized by writing scripts to +override the default behaviour. These scripts are (in general) kept on the boot +medium, in the 'larch' directory. As these are shell scripts and their use requires +some knowledge of the inner workings of the <em>larch</em> live system, it will +almost certainly be necessary to read the existing <em>larch</em> scripts where the +custom scripts are 'sourced' if you want to +write your own scripts to change the behaviour of the <em>larch</em> live system. +</p> +<ul> + <li><strong>session-save</strong> + <p>Used in <strong>/opt/larch-live/session-save/saveovl</strong>. This script can be + used to customize the creation of the new overlay archive, e.g. by + specifying a new location. The default is 'overlay.ovl' on the boot medium. + </p> + </li> + <li><strong>save-menu</strong> + <p>Used in <strong>/opt/larch-live/session-save/saveovl</strong>. This script can be + used to further customize the creation of the new overlay archive, e.g. by + providing an alternative session save menu. Note that if the + <strong>session-save</strong> script specified an alternative device path + for saving the overlay, this script will be sought in the 'larch' directory + on that path. + </p> + </li> + <li><strong>merge-adjust</strong> + <p>Used in <strong>/opt/larch-live/session-save/merge_overlay</strong>. This script can be + used to further customize aspects of the overlay merging process. Note that if the + <strong>session-save</strong> script specified an alternative device path + for saving the overlay, this script will be sought in the 'larch' directory + on that path. + </p> + </li> + <li><strong>boot-init</strong> + <p>In initramfs hook <strong>larch3</strong>. This script allows adjustment of + the overlay handling during the boot process, e.g. getting them from another + path. + Note that the shell environment here is that of the initramfs and thus + very limited. + </p> + </li> +</ul> + +<table style="text-align: left; width: 100%;" border="1" cellpadding="2" cellspacing="2"> + <tbody> + <tr> + <td><a href="larch_fstab.html">Previous: /etc/fstab</a></td> + + <td><a href="larch_docindex.html">Table of Contents</a></td> + + <td><a href="larch_ssh.html">Next: ssh access</a></td> + </tr> + </tbody> +</table> + +</body> +</html> |