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<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>systemd-readahead-replay.service</title><meta name="generator" content="DocBook XSL Stylesheets V1.77.1"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><a href="index.html">Index </a>·
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<a href="../libudev/index.html">gudev </a><span style="float:right">systemd 202</span><hr><div class="refentry"><a name="systemd-readahead-replay.service"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>systemd-readahead-replay.service, systemd-readahead-collect.service, systemd-readahead-done.service, systemd-readahead-done.timer, systemd-readahead — Disk read ahead logic</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><p><code class="filename">systemd-readahead-replay.service</code></p><p><code class="filename">systemd-readahead-collect.service</code></p><p><code class="filename">systemd-readahead-done.service</code></p><p><code class="filename">systemd-readahead-done.timer</code></p><div class="cmdsynopsis"><p><code class="command">/usr/lib/systemd/systemd-readahead/systemd-readahead</code> [OPTIONS...] COMMAND [DIRECTORY | FILE]</p></div></div><div class="refsect1"><a name="idp29646576"></a><h2>Description</h2><p><code class="filename">systemd-readahead-collect.service</code>
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is a service that collects disk usage patterns at boot
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time. <code class="filename">systemd-readahead-replay.service</code>
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is a service that replays this access data collected
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at the subsequent boot. Since disks tend to be
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magnitudes slower than RAM this is intended to improve
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boot speeds by pre-loading early at boot all data on
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disk that is known to be read for the complete boot
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process.</p><p><code class="filename">systemd-readahead-done.service</code>
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is executed a short while after boot completed and signals
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<code class="filename">systemd-readahead-collect.service</code>
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to end data collection. On this signal this service
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will then sort the collected disk accesses and store
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information about them disk in
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<code class="filename">/.readahead</code>.</p><p>Normally, both
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<code class="filename">systemd-readahead-collect.service</code>
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<code class="filename">systemd-readahead-replay.service</code>
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are activated at boot so that access patterns from the
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preceding boot are replayed and new data collected
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for the subsequent boot. However, on read-only media
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where the collected data cannot be stored it might
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be a good idea to disable
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<code class="filename">systemd-readahead-collect.service</code>.</p><p>On rotating media, when replaying disk accesses
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<code class="filename">systemd-readahead-replay.service</code>
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will order read requests by their location on disk. On
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non-rotating media, they will be ordered by their
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original access timestamp. If the file system supports
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<code class="filename">systemd-readahead-collect.service</code>
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will also defragment and rearrange files on disk to
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optimize subsequent boot times.</p></div><div class="refsect1"><a name="idp29428016"></a><h2>Options</h2><p><code class="filename">systemd-readahead</code> understands
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the following options:</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><code class="option">-h</code>, </span><span class="term"><code class="option">--help</code></span></dt><dd><p>Prints a short help text
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and exits.</p></dd><dt><span class="term"><code class="option">--max-files=</code></span></dt><dd><p>Maximum number of
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files to read ahead. Only valid
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for thes <span class="command"><strong>collect</strong></span>
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command.</p></dd><dt><span class="term"><code class="option">--file-size-max=</code></span></dt><dd><p>Maximum size of files
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(in bytes) to read ahead. Only valid
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for the <span class="command"><strong>collect</strong></span>
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and <span class="command"><strong>replay</strong></span>
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commands.</p></dd><dt><span class="term"><code class="option">--timeout=</code></span></dt><dd><p>Maximum time (in usec)
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to to spend collecting data. Only valid
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for the <span class="command"><strong>collect</strong></span>
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command.</p></dd></dl></div></div><div class="refsect1"><a name="idp30039376"></a><h2>Commands</h2><p>The following commands are understood by
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<code class="filename">systemd-readahead</code>:</p><div class="variablelist"><dl class="variablelist"><dt><span class="term"><span class="command"><strong>collect
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[<em class="replaceable"><code>DIRECTORY</code></em>]</strong></span></span></dt><dd><p>Collect read-ahead data on
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early boot. When terminating it will
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write out a pack file to the indicated
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directory containing the read-ahead
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data. </p></dd><dt><span class="term"><span class="command"><strong>replay
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[<em class="replaceable"><code>DIRECTORY</code></em>]</strong></span></span></dt><dd><p>Perform read-ahead on the
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specified directory tree.</p></dd><dt><span class="term"><span class="command"><strong>analyze
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[<em class="replaceable"><code>FILE</code></em>]</strong></span></span></dt><dd><p>Dumps the content of the
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read-ahead pack file to the
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terminal. The output lists
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approximately for each file
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how much will be read-ahead by
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the <span class="command"><strong>replay</strong></span>
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command.</p></dd></dl></div></div><div class="refsect1"><a name="idp29033456"></a><h2>See Also</h2><p>
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<a href="systemd.html"><span class="citerefentry"><span class="refentrytitle">systemd</span>(1)</span></a>
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</p></div></div></body></html>
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