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  <a href="../libudev/index.html">gudev </a><span style="float:right">systemd 208</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="idm274684861104"></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="idm274688754352"></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="-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>Prints a short help text
                                and exits.</p></dd><dt id="--max-files="><span class="term"><code class="option">--max-files=</code></span><a class="headerlink" title="Permalink to this term" href="#--max-files=">¶</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></dl></div></div><div class="refsect1"><a name="idm274688742560"></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="idm274688724480"></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>
Commit	Line	Data
663996b3 MS	1	<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>
	2	a.headerlink {
	3	color: #c60f0f;
	4	font-size: 0.8em;
	5	padding: 0 4px 0 4px;
	6	text-decoration: none;
	7	visibility: hidden;
	8	}
	9
	10	a.headerlink:hover {
	11	background-color: #c60f0f;
	12	color: white;
	13	}
	14
	15	h1:hover > a.headerlink, h2:hover > a.headerlink, h3:hover > a.headerlink, dt:hover > a.headerlink {
	16	visibility: visible;
	17	}
	18	</style><a href="index.html">Index </a>·
	19	<a href="systemd.directives.html">Directives </a>·
	20	<a href="../python-systemd/index.html">Python </a>·
	21	<a href="../libudev/index.html">libudev </a>·
14228c0d	22	<a href="../libudev/index.html">gudev </a><span style="float:right">systemd 208</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="idm274684861104"></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>
663996b3 MS	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
14228c0d	27	magnitudes slower than RAM, this is intended to improve
663996b3 MS	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>
14228c0d	33	to end data collection. On this signal, this service
663996b3	34	will then sort the collected disk accesses and store
14228c0d	35	information about them in
663996b3 MS	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
14228c0d	43	where the collected data cannot be stored, it might
663996b3 MS	44	be a good idea to disable
663996b3 MS	45	<code class="filename">systemd-readahead-collect.service</code>.</p><p>On rotating media, when replaying disk accesses
14228c0d	46	at early boot,
663996b3 MS	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
14228c0d	51	it,
663996b3 MS	52	<code class="filename">systemd-readahead-collect.service</code>
663996b3 MS	53	will also defragment and rearrange files on disk to
14228c0d	54	optimize subsequent boot times.</p></div><div class="refsect1"><a name="idm274688754352"></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
663996b3 MS	55	the following options:</p><div class="variablelist"><dl class="variablelist"><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>Prints a short help text
	56	and exits.</p></dd><dt id="--max-files="><span class="term"><code class="option">--max-files=</code></span><a class="headerlink" title="Permalink to this term" href="#--max-files=">¶</a></dt><dd><p>Maximum number of
	57	files to read ahead. Only valid
	58	for thes <span class="command"><strong>collect</strong></span>
	59	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
14228c0d	60	in bytes to read ahead. Only valid
663996b3 MS	61	for the <span class="command"><strong>collect</strong></span>
663996b3 MS	62	and <span class="command"><strong>replay</strong></span>
14228c0d MB	63	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
14228c0d MB	64	to spend collecting data. Only valid
663996b3	65	for the <span class="command"><strong>collect</strong></span>
14228c0d	66	command.</p></dd></dl></div></div><div class="refsect1"><a name="idm274688742560"></a><h2 id="Commands">Commands<a class="headerlink" title="Permalink to this headline" href="#Commands">¶</a></h2><p>The following commands are understood by
663996b3 MS	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
14228c0d	70	early boot. When terminating, it will
663996b3 MS	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
14228c0d MB	80	terminal. For each file, the
	81	output lists approximately how
	82	much will be read ahead by
663996b3	83	the <span class="command"><strong>replay</strong></span>
14228c0d	84	command.</p></dd></dl></div></div><div class="refsect1"><a name="idm274688724480"></a><h2 id="See Also">See Also<a class="headerlink" title="Permalink to this headline" href="#See%20Also">¶</a></h2><p>
663996b3 MS	85	<a href="systemd.html"><span class="citerefentry"><span class="refentrytitle">systemd</span>(1)</span></a>
663996b3 MS	86	</p></div></div></body></html>