man: document the readahead services
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Lennart Poettering
parent
0127336c01
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56a379a97e
15
Makefile.am
15
Makefile.am
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@ -2461,7 +2461,20 @@ EXTRA_DIST += \
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MANPAGES += \
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man/sd_readahead.3 \
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man/sd-readahead.7
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man/sd-readahead.7 \
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man/systemd-readahead-replay.service.8
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MANPAGES_ALIAS += \
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man/systemd-readahead-collect.service.8 \
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man/systemd-readahead-done.service.8 \
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man/systemd-readahead-done.timer.8 \
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man/systemd-readahead.8
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man/systemd-readahead-collect.service.8: man/systemd-readahead-replay.service.8
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man/systemd-readahead-done.service.8: man/systemd-readahead-replay.service.8
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man/systemd-readahead-done.timer.8: man/systemd-readahead-replay.service.8
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man/systemd-readahead.8: man/systemd-readahead-replay.service.8
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endif
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# ------------------------------------------------------------------------------
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@ -0,0 +1,113 @@
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<?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">
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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>systemd 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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preceeding 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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@ -7,6 +7,7 @@
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[Unit]
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Description=Collect Read-Ahead Data
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Documentation=man:systemd-readahead-replay.service(8)
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DefaultDependencies=no
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Wants=systemd-readahead-done.timer
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Conflicts=shutdown.target
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@ -7,6 +7,7 @@
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[Unit]
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Description=Stop Read-Ahead Data Collection
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Documentation=man:systemd-readahead-replay.service(8)
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DefaultDependencies=no
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Conflicts=shutdown.target
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After=default.target
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@ -7,6 +7,7 @@
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[Unit]
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Description=Stop Read-Ahead Data Collection 10s After Completed Startup
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Documentation=man:systemd-readahead-replay.service(8)
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DefaultDependencies=no
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Conflicts=shutdown.target
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After=default.target
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@ -7,6 +7,7 @@
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[Unit]
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Description=Replay Read-Ahead Data
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Documentation=man:systemd-readahead-replay.service(8)
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DefaultDependencies=no
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Conflicts=shutdown.target
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Before=sysinit.target shutdown.target
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