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diff --git a/build_tools/l7/larch0/docs/html/larch_sessionsave.html b/build_tools/l7/larch0/docs/html/larch_sessionsave.html new file mode 100644 index 0000000..2f2ca95 --- /dev/null +++ b/build_tools/l7/larch0/docs/html/larch_sessionsave.html @@ -0,0 +1,191 @@ +<!DOCTYPE html PUBLIC "-//W3C//DTD XHTML 1.0 Strict//EN" "http://www.w3.org/TR/xhtml1/xhtml1-strict.dtd"> +<html xmlns="http://www.w3.org/1999/xhtml" xml:lang="en" lang="en"> + +<html> +<head> +<meta http-equiv="Content-type" content="text/html; charset=utf-8" /> +<title>Saving a session back to the boot device (or even somewhere else)</title> +<!-- (en) Add your meta data here --> + +<link href="css/larchdocs.css" rel="stylesheet" type="text/css"/> +<!--[if lte IE 7]> +<link href="css/yaml/core/iehacks.css" rel="stylesheet" type="text/css" /> +<![endif]--> +</head> + +<body> +<!-- skip link navigation --> +<ul id="skiplinks"> + <li><a class="skip" href="#col1">Skip to main content (Press Enter).</a></li> +</ul> + +<div class="page_margins"> + <div class="page"> + <div id="top"><div id="tm"></div></div> + <!-- begin: #col1 --> + <div id="col1" role="main"> + <div id="col1_content"> + <div id="header" role="banner"> + <h1><span><em>live Arch Linux</em> builder</span></h1> + </div> + + <!-- begin: #col3 navigation column --> + <div id="col3" role="complementary"> + <div id="col3_content"> + <img class="indent2" alt="larch logo" src="css/screen/larch150x.png" width="150" height="150" /> + <div class="vlist"> + <ul> + <li><a href="index.html"><h6>Table Of Contents</h6></a></li> + <li><a href="larch_ssh.html"><h6>Next:</h6> + <div class="indent1">ssh access</div></a></li> + <li><a href="larch_live_system.html"><h6>Previous:</h6> + <div class="indent1">Structure of a larch live system</div></a></li> + </ul> + </div> + </div> + </div> + <!-- end: #col3 --> + +<div class="larchdocs"> +<h2 id="pagetitle" level="1">Saving a session back to the boot device (or even somewhere else)</h2> + +<p>An easy way to create a customized <em>live</em> system is to start from an +existing one, make whatever changes you like, and then save the result back to +the boot device. Of course, for this you need a writeable boot device, e.g. +a USB-stick. +</p> + +<h3><a name="overlays"></a>Overlay archives</h3> + +<p>In <em>larch</em> the uppermost layer in the union file-system is in +<em>tmpfs</em> and can (optionally) be saved at shutdown to the boot medium. +It is <em>compressed</em> using <em>tar</em> and <em>lzop</em> to the file +'overlay.tar.lzo'. When the system next boots this file will then be +unpacked into the initially empty top layer. +</p> + +<p>This is handled primarily by the 'shutdown2' script, supplied in the +'larch-live' package. It is called from a hook function in 'etc/rc.shutdown'. +If the medium is writeable and contains a file 'larch/save', the user is +offered the possibility of saving this overlay archive, thus saving the +current state. +</p> + +<p>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 with the middle (<em>squashfs</em>) <em>union</em> layer, +<strong>mods.sqf</strong> (which is normally not copied to memory), +thus restoring the rapid load and save times for <strong>overlay.tar.lzo</strong>, +and maximizing the available memory. I call this process +'overlay merging', and it is offered as a shutdown option. The script +'merge_overlay' (in the 'larch-live' package) provides this facility. +It takes longer to execute than a normal session save, so it should probably +not be used for every session saving operation, but just when the top overlay +gets too big. Note that use of the overlay merging feature creates an +additional layer in the <em>union</em>, 'filter.sqf'. This contains only +'whiteout' files to cover up overwritten data in the underlying 'system.sqf'. +Unlike in previous <em>larch</em> versions the 'mods.sqf' archive contains +no 'whiteouts'. It is hoped that this new structure will cure the +problems experienced in these earlier versions. +</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 is possible to perform package addition and removal in the <em>live</em> +system, but one should be aware that packages in the base system are not actually +replaced, just (effectively) hidden, so that the space usage might become a +consideration. Also the handling of kernel updates must be handled in a special +way, because it is stored outside the root file-system, on the boot medium +and needs a separate mechanism to save it at shutdown. It should be fairly +transparent to the user, but under certain circumstances it might be necessary +to bear this in mind. +</p> + +<p>At some point, after extensive updating, it might be desirable to completely +<a href="larch_rebuild.html">rebuild the system</a>, so that also +'system.sqf' is recreated. This will require quite a bit of space, +but should otherwise pose no great problems. +</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. This +will be generated automatically if installing to a partition (i.e. if not +building an <em>iso</em>) and if there is no 'nosave' file in the profile. +The gui provides a button to create and delete this 'nosave' file, +thus disabling or enabling session saving on the created medium. +</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 live </em>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>live</em> system in +this respect. All these scripts are found in the 'larch-live' package. +</p> +<ul> + <li><strong>session-save0</strong> + <p>Used in <strong>session-save/shutdown2</strong> (in function 'checkse'). + 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.tar.lzo' on the boot medium. + </p> + </li> + <li><strong>save-menu</strong> + <p>Used in <strong>session-save/shutdown2</strong> (in function + 'session-save'). 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-save0</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><a name="boot-init"></a><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> + +</div> + + + <div class="topref"><a href="#top">Top</a></div> + </div> + <!-- begin: #footer --> + <div id="footer"> + <div id="footer-content" role="contentinfo">© 2010 Michael Towers<br /> + Page layout assisted by <a href="http://www.yaml.de/">YAML</a> and + <a href="http://www.kuwata-lab.com/tenjin/">pyTenjin</a> + </div> + </div> + <!-- end: #footer --> + </div> + <!-- end: #col1 --> + <div id="bottom"><div id="bl"><div id="bm"></div></div></div> + </div> +</div> +<!-- full skiplink functionality in webkit browsers --> +<script src="css/yaml/core/js/webkit-focusfix.js" type="text/javascript"></script> +</body> +</html> |