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1 | <?xml version='1.0'?> <!--*-nxml-*--> |
2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" | |
3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> | |
4 | ||
5 | <!-- | |
6 | This file is part of systemd. | |
7 | ||
8 | Copyright 2010 Lennart Poettering | |
9 | ||
10 | systemd is free software; you can redistribute it and/or modify it | |
11 | under the terms of the GNU Lesser General Public License as published by | |
12 | the Free Software Foundation; either version 2.1 of the License, or | |
13 | (at your option) any later version. | |
14 | ||
15 | systemd is distributed in the hope that it will be useful, but | |
16 | WITHOUT ANY WARRANTY; without even the implied warranty of | |
17 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
18 | Lesser General Public License for more details. | |
19 | ||
20 | You should have received a copy of the GNU Lesser General Public License | |
21 | along with systemd; If not, see <http://www.gnu.org/licenses/>. | |
22 | --> | |
23 | ||
56ba3c78 | 24 | <refentry id="systemd-readahead-replay.service" conditional='ENABLE_READAHEAD'> |
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25 | |
26 | <refentryinfo> | |
27 | <title>systemd-readahead-replay.service</title> | |
28 | <productname>systemd</productname> | |
29 | ||
30 | <authorgroup> | |
31 | <author> | |
32 | <contrib>Developer</contrib> | |
33 | <firstname>Lennart</firstname> | |
34 | <surname>Poettering</surname> | |
35 | <email>lennart@poettering.net</email> | |
36 | </author> | |
37 | </authorgroup> | |
38 | </refentryinfo> | |
39 | ||
40 | <refmeta> | |
41 | <refentrytitle>systemd-readahead-replay.service</refentrytitle> | |
42 | <manvolnum>8</manvolnum> | |
43 | </refmeta> | |
44 | ||
45 | <refnamediv> | |
46 | <refname>systemd-readahead-replay.service</refname> | |
47 | <refname>systemd-readahead-collect.service</refname> | |
48 | <refname>systemd-readahead-done.service</refname> | |
49 | <refname>systemd-readahead-done.timer</refname> | |
50 | <refname>systemd-readahead</refname> | |
34511ca7 | 51 | <refpurpose>Disk read ahead logic</refpurpose> |
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52 | </refnamediv> |
53 | ||
54 | <refsynopsisdiv> | |
55 | <para><filename>systemd-readahead-replay.service</filename></para> | |
56 | <para><filename>systemd-readahead-collect.service</filename></para> | |
57 | <para><filename>systemd-readahead-done.service</filename></para> | |
58 | <para><filename>systemd-readahead-done.timer</filename></para> | |
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59 | <cmdsynopsis> |
60 | <command>/usr/lib/systemd/systemd-readahead/systemd-readahead</command> | |
61 | <arg choice="opt" rep="repeat">OPTIONS</arg> | |
62 | <arg choice="plain">COMMAND</arg> | |
63 | <arg choice="opt">DIRECTORY | FILE</arg> | |
64 | </cmdsynopsis> | |
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65 | </refsynopsisdiv> |
66 | ||
67 | <refsect1> | |
68 | <title>Description</title> | |
69 | ||
70 | <para><filename>systemd-readahead-collect.service</filename> | |
71 | is a service that collects disk usage patterns at boot | |
72 | time. <filename>systemd-readahead-replay.service</filename> | |
73 | is a service that replays this access data collected | |
74 | at the subsequent boot. Since disks tend to be | |
75 | magnitudes slower than RAM this is intended to improve | |
76 | boot speeds by pre-loading early at boot all data on | |
77 | disk that is known to be read for the complete boot | |
78 | process.</para> | |
79 | ||
80 | <para><filename>systemd-readahead-done.service</filename> | |
81 | is executed a short while after boot completed and signals | |
82 | <filename>systemd-readahead-collect.service</filename> | |
83 | to end data collection. On this signal this service | |
84 | will then sort the collected disk accesses and store | |
85 | information about them disk in | |
86 | <filename>/.readahead</filename>.</para> | |
87 | ||
88 | <para>Normally, both | |
89 | <filename>systemd-readahead-collect.service</filename> | |
90 | and | |
91 | <filename>systemd-readahead-replay.service</filename> | |
92 | are activated at boot so that access patterns from the | |
49f43d5f | 93 | preceding boot are replayed and new data collected |
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94 | for the subsequent boot. However, on read-only media |
95 | where the collected data cannot be stored it might | |
96 | be a good idea to disable | |
97 | <filename>systemd-readahead-collect.service</filename>.</para> | |
98 | ||
99 | <para>On rotating media, when replaying disk accesses | |
100 | at early boot | |
101 | <filename>systemd-readahead-replay.service</filename> | |
102 | will order read requests by their location on disk. On | |
103 | non-rotating media, they will be ordered by their | |
104 | original access timestamp. If the file system supports | |
105 | it | |
106 | <filename>systemd-readahead-collect.service</filename> | |
107 | will also defragment and rearrange files on disk to | |
108 | optimize subsequent boot times.</para> | |
109 | </refsect1> | |
110 | ||
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111 | <refsect1> |
112 | <title>Options</title> | |
113 | ||
114 | <para><filename>systemd-readahead</filename> understands | |
115 | the following options:</para> | |
116 | ||
117 | <variablelist> | |
118 | <varlistentry> | |
119 | <term><option>-h</option></term> | |
120 | <term><option>--help</option></term> | |
121 | ||
122 | <listitem><para>Prints a short help text | |
123 | and exits.</para></listitem> | |
124 | </varlistentry> | |
125 | ||
126 | <varlistentry> | |
127 | <term><option>--max-files=</option></term> | |
128 | ||
129 | <listitem><para>Maximum number of | |
130 | files to read ahead. Only valid | |
131 | for thes <command>collect</command> | |
132 | command.</para></listitem> | |
133 | </varlistentry> | |
134 | ||
135 | <varlistentry> | |
136 | <term><option>--file-size-max=</option></term> | |
137 | ||
138 | <listitem><para>Maximum size of files | |
139 | (in bytes) to read ahead. Only valid | |
140 | for the <command>collect</command> | |
141 | and <command>replay</command> | |
142 | commands.</para></listitem> | |
143 | </varlistentry> | |
144 | ||
145 | <varlistentry> | |
146 | <term><option>--timeout=</option></term> | |
147 | ||
148 | <listitem><para>Maximum time (in usec) | |
149 | to to spend collecting data. Only valid | |
150 | for the <command>collect</command> | |
151 | command.</para></listitem> | |
152 | </varlistentry> | |
153 | </variablelist> | |
154 | ||
155 | </refsect1> | |
156 | ||
157 | <refsect1> | |
158 | <title>Commands</title> | |
159 | ||
160 | <para>The following commands are understood by | |
161 | <filename>systemd-readahead</filename>:</para> <variablelist> | |
162 | <varlistentry> | |
163 | <term><command>collect | |
164 | [<replaceable>DIRECTORY</replaceable>]</command></term> | |
165 | <listitem> | |
166 | <para>Collect read-ahead data on | |
167 | early boot. When terminating it will | |
168 | write out a pack file to the indicated | |
169 | directory containing the read-ahead | |
170 | data. </para> | |
171 | </listitem> | |
172 | </varlistentry> | |
173 | ||
174 | <varlistentry> | |
175 | <term><command>replay | |
176 | [<replaceable>DIRECTORY</replaceable>]</command></term> | |
177 | <listitem> | |
178 | <para>Perform read-ahead on the | |
179 | specified directory tree.</para> | |
180 | </listitem> | |
181 | </varlistentry> | |
182 | ||
183 | <varlistentry> | |
184 | <term><command>analyze | |
185 | [<replaceable>FILE</replaceable>]</command></term> | |
186 | <listitem> | |
187 | <para>Dumps the content of the | |
188 | read-ahead pack file to the | |
189 | terminal. The output lists | |
190 | approximately for each file | |
191 | how much will be read-ahead by | |
192 | the <command>replay</command> | |
193 | command.</para> | |
194 | </listitem> | |
195 | </varlistentry> | |
196 | ||
197 | </variablelist> | |
198 | </refsect1> | |
199 | ||
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200 | <refsect1> |
201 | <title>See Also</title> | |
202 | <para> | |
203 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
204 | </para> | |
205 | </refsect1> | |
206 | ||
207 | </refentry> |