208 lines
9.3 KiB
XML
208 lines
9.3 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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This file is part of systemd.
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Copyright 2010 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="systemd-readahead-replay.service" conditional='ENABLE_READAHEAD'>
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<refentryinfo>
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<title>systemd-readahead-replay.service</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>systemd-readahead-replay.service</refentrytitle>
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<manvolnum>8</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>systemd-readahead-replay.service</refname>
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<refname>systemd-readahead-collect.service</refname>
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<refname>systemd-readahead-done.service</refname>
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<refname>systemd-readahead-done.timer</refname>
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<refname>systemd-readahead</refname>
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<refpurpose>Disk read ahead logic</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<para><filename>systemd-readahead-replay.service</filename></para>
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<para><filename>systemd-readahead-collect.service</filename></para>
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<para><filename>systemd-readahead-done.service</filename></para>
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<para><filename>systemd-readahead-done.timer</filename></para>
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<cmdsynopsis>
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<command>/usr/lib/systemd/systemd-readahead/systemd-readahead</command>
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<arg choice="opt" rep="repeat">OPTIONS</arg>
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<arg choice="plain">COMMAND</arg>
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<arg choice="opt">DIRECTORY | FILE</arg>
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</cmdsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><filename>systemd-readahead-collect.service</filename>
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is a service that collects disk usage patterns at boot
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time. <filename>systemd-readahead-replay.service</filename>
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is a service that replays this access data collected
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at the subsequent boot. Since disks tend to be
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magnitudes slower than RAM, this is intended to improve
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boot speeds by pre-loading early at boot all data on
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disk that is known to be read for the complete boot
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process.</para>
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<para><filename>systemd-readahead-done.service</filename>
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is executed a short while after boot completed and signals
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<filename>systemd-readahead-collect.service</filename>
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to end data collection. On this signal, this service
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will then sort the collected disk accesses and store
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information about them in
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<filename>/.readahead</filename>.</para>
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<para>Normally, both
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<filename>systemd-readahead-collect.service</filename>
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and
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<filename>systemd-readahead-replay.service</filename>
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are activated at boot so that access patterns from the
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preceding boot are replayed and new data collected
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for the subsequent boot. However, on read-only media
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where the collected data cannot be stored, it might
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be a good idea to disable
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<filename>systemd-readahead-collect.service</filename>.</para>
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<para>On rotating media, when replaying disk accesses
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at early boot,
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<filename>systemd-readahead-replay.service</filename>
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will order read requests by their location on disk. On
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non-rotating media, they will be ordered by their
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original access timestamp. If the file system supports
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it,
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<filename>systemd-readahead-collect.service</filename>
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will also defragment and rearrange files on disk to
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optimize subsequent boot times.</para>
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</refsect1>
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<refsect1>
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<title>Options</title>
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<para><filename>systemd-readahead</filename> understands
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the following options:</para>
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<variablelist>
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<varlistentry>
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<term><option>-h</option></term>
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<term><option>--help</option></term>
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<listitem><para>Prints a short help text
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and exits.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--max-files=</option></term>
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<listitem><para>Maximum number of
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files to read ahead. Only valid
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for thes <command>collect</command>
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command.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--file-size-max=</option></term>
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<listitem><para>Maximum size of files
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in bytes to read ahead. Only valid
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for the <command>collect</command>
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and <command>replay</command>
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commands.</para></listitem>
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</varlistentry>
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<varlistentry>
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<term><option>--timeout=</option></term>
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<listitem><para>Maximum time in microseconds
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to spend collecting data. Only valid
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for the <command>collect</command>
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command.</para></listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>Commands</title>
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<para>The following commands are understood by
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<filename>systemd-readahead</filename>:</para> <variablelist>
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<varlistentry>
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<term><command>collect
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[<replaceable>DIRECTORY</replaceable>]</command></term>
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<listitem>
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<para>Collect read-ahead data on
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early boot. When terminating, it will
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write out a pack file to the indicated
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directory containing the read-ahead
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data. </para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><command>replay
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[<replaceable>DIRECTORY</replaceable>]</command></term>
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<listitem>
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<para>Perform read-ahead on the
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specified directory tree.</para>
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</listitem>
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</varlistentry>
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<varlistentry>
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<term><command>analyze
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[<replaceable>FILE</replaceable>]</command></term>
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<listitem>
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<para>Dumps the content of the
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read-ahead pack file to the
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terminal. For each file, the
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output lists approximately how
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much will be read ahead by
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the <command>replay</command>
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command.</para>
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</listitem>
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</varlistentry>
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</variablelist>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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