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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 V1.78.1"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><style>
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</style><a href="index.html">Index </a>·
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<a href="../libudev/index.html">gudev </a><span style="float:right">systemd 215</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="idm214193075936"></a><h2 id="Description">Description<a class="headerlink" title="Permalink to this headline" href="#Description">¶</a></h2><p><code class="filename">systemd-readahead-collect.service</code>
is a service that collects disk usage patterns at boot
time. <code class="filename">systemd-readahead-replay.service</code>
is a service that replays this access data collected
at the subsequent boot. Since disks tend to be
magnitudes slower than RAM, this is intended to improve
boot speeds by pre-loading early at boot all data on
disk that is known to be read for the complete boot
process.</p><p><code class="filename">systemd-readahead-done.service</code>
is executed a short while after boot completed and signals
<code class="filename">systemd-readahead-collect.service</code>
to end data collection. On this signal, this service
will then sort the collected disk accesses and store
information about them in
<code class="filename">/.readahead</code>.</p><p>Normally, both
<code class="filename">systemd-readahead-collect.service</code>
and
<code class="filename">systemd-readahead-replay.service</code>
are activated at boot so that access patterns from the
preceding boot are replayed and new data collected
for the subsequent boot. However, on read-only media
where the collected data cannot be stored, it might
be a good idea to disable
<code class="filename">systemd-readahead-collect.service</code>.</p><p>On rotating media, when replaying disk accesses
at early boot,
<code class="filename">systemd-readahead-replay.service</code>
will order read requests by their location on disk. On
non-rotating media, they will be ordered by their
original access timestamp. If the file system supports
it,
<code class="filename">systemd-readahead-collect.service</code>
will also defragment and rearrange files on disk to
optimize subsequent boot times.</p></div><div class="refsect1"><a name="idm214197017776"></a><h2 id="Options">Options<a class="headerlink" title="Permalink to this headline" href="#Options">¶</a></h2><p><code class="filename">systemd-readahead</code> understands
the following options:</p><div class="variablelist"><dl class="variablelist"><dt id="--files-max="><span class="term"><code class="option">--files-max=</code></span><a class="headerlink" title="Permalink to this term" href="#--files-max=">¶</a></dt><dd><p>Maximum number of
files to read ahead. Only valid
for thes <span class="command"><strong>collect</strong></span>
command.</p></dd><dt id="--file-size-max="><span class="term"><code class="option">--file-size-max=</code></span><a class="headerlink" title="Permalink to this term" href="#--file-size-max=">¶</a></dt><dd><p>Maximum size of files
in bytes to read ahead. Only valid
for the <span class="command"><strong>collect</strong></span>
and <span class="command"><strong>replay</strong></span>
commands.</p></dd><dt id="--timeout="><span class="term"><code class="option">--timeout=</code></span><a class="headerlink" title="Permalink to this term" href="#--timeout=">¶</a></dt><dd><p>Maximum time in microseconds
to spend collecting data. Only valid
for the <span class="command"><strong>collect</strong></span>
command.</p></dd><dt id="-h"><span class="term"><code class="option">-h</code>, </span><span class="term"><code class="option">--help</code></span><a class="headerlink" title="Permalink to this term" href="#-h">¶</a></dt><dd><p><a name="help-text"></a>Print a short help text and exit.
</p></dd><dt id="--version"><span class="term"><code class="option">--version</code></span><a class="headerlink" title="Permalink to this term" href="#--version">¶</a></dt><dd><p><a name="version-text"></a>Print a short version string and exit.</p></dd></dl></div></div><div class="refsect1"><a name="idm214197006432"></a><h2 id="Commands">Commands<a class="headerlink" title="Permalink to this headline" href="#Commands">¶</a></h2><p>The following commands are understood by
<code class="filename">systemd-readahead</code>:</p><div class="variablelist"><dl class="variablelist"><dt id="collect
[DIRECTORY]"><span class="term"><span class="command"><strong>collect
[<em class="replaceable"><code>DIRECTORY</code></em>]</strong></span></span><a class="headerlink" title="Permalink to this term" href="#collect%0A%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%5BDIRECTORY%5D">¶</a></dt><dd><p>Collect read-ahead data on
early boot. When terminating, it will
write out a pack file to the indicated
directory containing the read-ahead
data. </p></dd><dt id="replay
[DIRECTORY]"><span class="term"><span class="command"><strong>replay
[<em class="replaceable"><code>DIRECTORY</code></em>]</strong></span></span><a class="headerlink" title="Permalink to this term" href="#replay%0A%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%5BDIRECTORY%5D">¶</a></dt><dd><p>Perform read-ahead on the
specified directory tree.</p></dd><dt id="analyze
[FILE]"><span class="term"><span class="command"><strong>analyze
[<em class="replaceable"><code>FILE</code></em>]</strong></span></span><a class="headerlink" title="Permalink to this term" href="#analyze%0A%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%20%5BFILE%5D">¶</a></dt><dd><p>Dumps the content of the
read-ahead pack file to the
terminal. For each file, the
output lists approximately how
much will be read ahead by
the <span class="command"><strong>replay</strong></span>
command.</p></dd></dl></div></div><div class="refsect1"><a name="idm214196988320"></a><h2 id="See Also">See Also<a class="headerlink" title="Permalink to this headline" href="#See%20Also">¶</a></h2><p>
<a href="systemd.html"><span class="citerefentry"><span class="refentrytitle">systemd</span>(1)</span></a>
</p></div></div></body></html>
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