56ba3c78ae
man rules were repeating the same information in too many places, which was error prone. Those rules can be easily generated from .xml files. For efficiency and because python is not a required dependency, Makefile-man.am is only regenerated when requested with make update-man-list If no metadata in man/*.xml changed, this file should not change. So only when a new man page or a new alias is added, this file should show up in 'git diff'. The change should then be committed. If the support for building from git without python was dropped, we could drop Makefile-man.am from version control. This would also increase the partial build time (since more stuff would be rebuild whenever sources in man/*.xml would be modified), so it would probably wouldn't be worth it.
114 lines
5 KiB
XML
114 lines
5 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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<para><filename>/usr/lib/systemd/systemd-readahead</filename></para>
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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 disk 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>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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