man/systemd-readahead.html

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  22   <a href="../libudev/index.html">gudev </a><span style="float:right">systemd 214</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="idm214173363184"></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>
  23                 is a service that collects disk usage patterns at boot
  24                 time. <code class="filename">systemd-readahead-replay.service</code>
  25                 is a service that replays this access data collected
  26                 at the subsequent boot. Since disks tend to be
  27                 magnitudes slower than RAM, this is intended to improve
  28                 boot speeds by pre-loading early at boot all data on
  29                 disk that is known to be read for the complete boot
  30                 process.</p><p><code class="filename">systemd-readahead-done.service</code>
  31                 is executed a short while after boot completed and signals
  32                 <code class="filename">systemd-readahead-collect.service</code>
  33                 to end data collection. On this signal, this service
  34                 will then sort the collected disk accesses and store
  35                 information about them in
  36                 <code class="filename">/.readahead</code>.</p><p>Normally, both
  37                 <code class="filename">systemd-readahead-collect.service</code>
  38                 and
  39                 <code class="filename">systemd-readahead-replay.service</code>
  40                 are activated at boot so that access patterns from the
  41                 preceding boot are replayed and new data collected
  42                 for the subsequent boot. However, on read-only media
  43                 where the collected data cannot be stored, it might
  44                 be a good idea to disable
  45                 <code class="filename">systemd-readahead-collect.service</code>.</p><p>On rotating media, when replaying disk accesses
  46                 at early boot,
  47                 <code class="filename">systemd-readahead-replay.service</code>
  48                 will order read requests by their location on disk. On
  49                 non-rotating media, they will be ordered by their
  50                 original access timestamp. If the file system supports
  51                 it,
  52                 <code class="filename">systemd-readahead-collect.service</code>
  53                 will also defragment and rearrange files on disk to
  54                 optimize subsequent boot times.</p></div><div class="refsect1"><a name="idm214173352320"></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
  55                 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
  56                                 files to read ahead. Only valid
  57                                 for thes <span class="command"><strong>collect</strong></span>
  58                                 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
  59                                 in bytes to read ahead. Only valid
  60                                 for the <span class="command"><strong>collect</strong></span>
  61                                 and <span class="command"><strong>replay</strong></span>
  62                                 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
  63                                 to spend collecting data. Only valid
  64                                 for the <span class="command"><strong>collect</strong></span>
  65                                 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.
  66     </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="idm214177240336"></a><h2 id="Commands">Commands<a class="headerlink" title="Permalink to this headline" href="#Commands">¶</a></h2><p>The following commands are understood by
  67                 <code class="filename">systemd-readahead</code>:</p><div class="variablelist"><dl class="variablelist"><dt id="collect
  68                                 [DIRECTORY]"><span class="term"><span class="command"><strong>collect
  69                                 [<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
  70                                         early boot. When terminating, it will
  71                                         write out a pack file to the indicated
  72                                         directory containing the read-ahead
  73                                         data. </p></dd><dt id="replay
  74                                 [DIRECTORY]"><span class="term"><span class="command"><strong>replay
  75                                 [<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
  76                                         specified directory tree.</p></dd><dt id="analyze
  77                                 [FILE]"><span class="term"><span class="command"><strong>analyze
  78                                 [<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
  79                                         read-ahead pack file to the
  80                                         terminal. For each file, the
  81                                         output lists approximately how
  82                                         much will be read ahead by
  83                                         the <span class="command"><strong>replay</strong></span>
  84                                         command.</p></dd></dl></div></div><div class="refsect1"><a name="idm214177222208"></a><h2 id="See Also">See Also<a class="headerlink" title="Permalink to this headline" href="#See%20Also">¶</a></h2><p>
  85                         <a href="systemd.html"><span class="citerefentry"><span class="refentrytitle">systemd</span>(1)</span></a>
  86                 </p></div></div></body></html>