man/systemd-readahead-replay.service.xml

   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
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   6   This file is part of systemd.
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   8   Copyright 2010 Lennart Poettering
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  23
  24 <refentry id="systemd-readahead-replay.service" conditional='ENABLE_READAHEAD'
  25           xmlns:xi="http://www.w3.org/2001/XInclude">
  26
  27         <refentryinfo>
  28                 <title>systemd-readahead-replay.service</title>
  29                 <productname>systemd</productname>
  30
  31                 <authorgroup>
  32                         <author>
  33                                 <contrib>Developer</contrib>
  34                                 <firstname>Lennart</firstname>
  35                                 <surname>Poettering</surname>
  36                                 <email>lennart@poettering.net</email>
  37                         </author>
  38                 </authorgroup>
  39         </refentryinfo>
  40
  41         <refmeta>
  42                 <refentrytitle>systemd-readahead-replay.service</refentrytitle>
  43                 <manvolnum>8</manvolnum>
  44         </refmeta>
  45
  46         <refnamediv>
  47                 <refname>systemd-readahead-replay.service</refname>
  48                 <refname>systemd-readahead-collect.service</refname>
  49                 <refname>systemd-readahead-done.service</refname>
  50                 <refname>systemd-readahead-done.timer</refname>
  51                 <refname>systemd-readahead</refname>
  52                 <refpurpose>Disk read ahead logic</refpurpose>
  53         </refnamediv>
  54
  55         <refsynopsisdiv>
  56                 <para><filename>systemd-readahead-replay.service</filename></para>
  57                 <para><filename>systemd-readahead-collect.service</filename></para>
  58                 <para><filename>systemd-readahead-done.service</filename></para>
  59                 <para><filename>systemd-readahead-done.timer</filename></para>
  60                 <cmdsynopsis>
  61                         <command>/usr/lib/systemd/systemd-readahead/systemd-readahead</command>
  62                         <arg choice="opt" rep="repeat">OPTIONS</arg>
  63                         <arg choice="plain">COMMAND</arg>
  64                         <arg choice="opt">DIRECTORY | FILE</arg>
  65                 </cmdsynopsis>
  66         </refsynopsisdiv>
  67
  68         <refsect1>
  69                 <title>Description</title>
  70
  71                 <para><filename>systemd-readahead-collect.service</filename>
  72                 is a service that collects disk usage patterns at boot
  73                 time. <filename>systemd-readahead-replay.service</filename>
  74                 is a service that replays this access data collected
  75                 at the subsequent boot. Since disks tend to be
  76                 magnitudes slower than RAM, this is intended to improve
  77                 boot speeds by pre-loading early at boot all data on
  78                 disk that is known to be read for the complete boot
  79                 process.</para>
  80
  81                 <para><filename>systemd-readahead-done.service</filename>
  82                 is executed a short while after boot completed and signals
  83                 <filename>systemd-readahead-collect.service</filename>
  84                 to end data collection. On this signal, this service
  85                 will then sort the collected disk accesses and store
  86                 information about them in
  87                 <filename>/.readahead</filename>.</para>
  88
  89                 <para>Normally, both
  90                 <filename>systemd-readahead-collect.service</filename>
  91                 and
  92                 <filename>systemd-readahead-replay.service</filename>
  93                 are activated at boot so that access patterns from the
  94                 preceding boot are replayed and new data collected
  95                 for the subsequent boot. However, on read-only media
  96                 where the collected data cannot be stored, it might
  97                 be a good idea to disable
  98                 <filename>systemd-readahead-collect.service</filename>.</para>
  99
 100                 <para>On rotating media, when replaying disk accesses
 101                 at early boot,
 102                 <filename>systemd-readahead-replay.service</filename>
 103                 will order read requests by their location on disk. On
 104                 non-rotating media, they will be ordered by their
 105                 original access timestamp. If the file system supports
 106                 it,
 107                 <filename>systemd-readahead-collect.service</filename>
 108                 will also defragment and rearrange files on disk to
 109                 optimize subsequent boot times.</para>
 110         </refsect1>
 111
 112         <refsect1>
 113                 <title>Options</title>
 114
 115                 <para><filename>systemd-readahead</filename> understands
 116                 the following options:</para>
 117
 118                 <variablelist>
 119                         <varlistentry>
 120                                 <term><option>--max-files=</option></term>
 121
 122                                 <listitem><para>Maximum number of
 123                                 files to read ahead. Only valid
 124                                 for thes <command>collect</command>
 125                                 command.</para></listitem>
 126                         </varlistentry>
 127
 128                         <varlistentry>
 129                                 <term><option>--file-size-max=</option></term>
 130
 131                                 <listitem><para>Maximum size of files
 132                                 in bytes to read ahead. Only valid
 133                                 for the <command>collect</command>
 134                                 and <command>replay</command>
 135                                 commands.</para></listitem>
 136                         </varlistentry>
 137
 138                         <varlistentry>
 139                                 <term><option>--timeout=</option></term>
 140
 141                                 <listitem><para>Maximum time in microseconds
 142                                 to spend collecting data. Only valid
 143                                 for the <command>collect</command>
 144                                 command.</para></listitem>
 145                         </varlistentry>
 146
 147                         <xi:include href="standard-options.xml" xpointer="help" />
 148                         <xi:include href="standard-options.xml" xpointer="version" />
 149                 </variablelist>
 150
 151         </refsect1>
 152
 153         <refsect1>
 154                 <title>Commands</title>
 155
 156                 <para>The following commands are understood by
 157                 <filename>systemd-readahead</filename>:</para> <variablelist>
 158                         <varlistentry>
 159                                 <term><command>collect
 160                                 [<replaceable>DIRECTORY</replaceable>]</command></term>
 161                                 <listitem>
 162                                         <para>Collect read-ahead data on
 163                                         early boot. When terminating, it will
 164                                         write out a pack file to the indicated
 165                                         directory containing the read-ahead
 166                                         data. </para>
 167                                 </listitem>
 168                         </varlistentry>
 169
 170                         <varlistentry>
 171                                 <term><command>replay
 172                                 [<replaceable>DIRECTORY</replaceable>]</command></term>
 173                                 <listitem>
 174                                         <para>Perform read-ahead on the
 175                                         specified directory tree.</para>
 176                                 </listitem>
 177                         </varlistentry>
 178
 179                         <varlistentry>
 180                                 <term><command>analyze
 181                                 [<replaceable>FILE</replaceable>]</command></term>
 182                                 <listitem>
 183                                         <para>Dumps the content of the
 184                                         read-ahead pack file to the
 185                                         terminal. For each file, the
 186                                         output lists approximately how
 187                                         much will be read ahead by
 188                                         the <command>replay</command>
 189                                         command.</para>
 190                                 </listitem>
 191                         </varlistentry>
 192
 193                 </variablelist>
 194         </refsect1>
 195
 196         <refsect1>
 197                 <title>See Also</title>
 198                 <para>
 199                         <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
 200                 </para>
 201         </refsect1>
 202
 203 </refentry>