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systemd/man/systemd-readahead-replay.service.xml

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man: document the readahead services
2012-06-26 20:16:00 +04:00
<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!--
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Copyright 2010 Lennart Poettering
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(at your option) any later version.
systemd is distributed in the hope that it will be useful, but
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build-sys: create Makefile-man.am automatically 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.
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<refentry id="systemd-readahead-replay.service" conditional='ENABLE_READAHEAD'>
man: document the readahead services
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<refentryinfo>
<title>systemd-readahead-replay.service</title>
<productname>systemd</productname>
<authorgroup>
<author>
<contrib>Developer</contrib>
<firstname>Lennart</firstname>
<surname>Poettering</surname>
<email>lennart@poettering.net</email>
</author>
</authorgroup>
</refentryinfo>
<refmeta>
<refentrytitle>systemd-readahead-replay.service</refentrytitle>
<manvolnum>8</manvolnum>
</refmeta>
<refnamediv>
<refname>systemd-readahead-replay.service</refname>
<refname>systemd-readahead-collect.service</refname>
<refname>systemd-readahead-done.service</refname>
<refname>systemd-readahead-done.timer</refname>
<refname>systemd-readahead</refname>
man: reword man page titles Make sure the man page titles are similar in style and capitalization so that our man page index looks pretty.
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<refpurpose>Disk read ahead logic</refpurpose>
man: document the readahead services
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</refnamediv>
<refsynopsisdiv>
<para><filename>systemd-readahead-replay.service</filename></para>
<para><filename>systemd-readahead-collect.service</filename></para>
<para><filename>systemd-readahead-done.service</filename></para>
<para><filename>systemd-readahead-done.timer</filename></para>
readahead: document options and commands.
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<cmdsynopsis>
<command>/usr/lib/systemd/systemd-readahead/systemd-readahead</command>
<arg choice="opt" rep="repeat">OPTIONS</arg>
<arg choice="plain">COMMAND</arg>
<arg choice="opt">DIRECTORY | FILE</arg>
</cmdsynopsis>
man: document the readahead services
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</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><filename>systemd-readahead-collect.service</filename>
is a service that collects disk usage patterns at boot
time. <filename>systemd-readahead-replay.service</filename>
is a service that replays this access data collected
at the subsequent boot. Since disks tend to be
magnitudes slower than RAM this is intended to improve
boot speeds by pre-loading early at boot all data on
disk that is known to be read for the complete boot
process.</para>
<para><filename>systemd-readahead-done.service</filename>
is executed a short while after boot completed and signals
<filename>systemd-readahead-collect.service</filename>
to end data collection. On this signal this service
will then sort the collected disk accesses and store
information about them disk in
<filename>/.readahead</filename>.</para>
<para>Normally, both
<filename>systemd-readahead-collect.service</filename>
and
<filename>systemd-readahead-replay.service</filename>
are activated at boot so that access patterns from the
Spelling fixes.
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preceding boot are replayed and new data collected
man: document the readahead services
2012-06-26 20:16:00 +04:00
for the subsequent boot. However, on read-only media
where the collected data cannot be stored it might
be a good idea to disable
<filename>systemd-readahead-collect.service</filename>.</para>
<para>On rotating media, when replaying disk accesses
at early boot
<filename>systemd-readahead-replay.service</filename>
will order read requests by their location on disk. On
non-rotating media, they will be ordered by their
original access timestamp. If the file system supports
it
<filename>systemd-readahead-collect.service</filename>
will also defragment and rearrange files on disk to
optimize subsequent boot times.</para>
</refsect1>
readahead: document options and commands.
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<refsect1>
<title>Options</title>
<para><filename>systemd-readahead</filename> understands
the following options:</para>
<variablelist>
<varlistentry>
<term><option>-h</option></term>
<term><option>--help</option></term>
<listitem><para>Prints a short help text
and exits.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--max-files=</option></term>
<listitem><para>Maximum number of
files to read ahead. Only valid
for thes <command>collect</command>
command.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--file-size-max=</option></term>
<listitem><para>Maximum size of files
(in bytes) to read ahead. Only valid
for the <command>collect</command>
and <command>replay</command>
commands.</para></listitem>
</varlistentry>
<varlistentry>
<term><option>--timeout=</option></term>
<listitem><para>Maximum time (in usec)
to to spend collecting data. Only valid
for the <command>collect</command>
command.</para></listitem>
</varlistentry>
</variablelist>
</refsect1>
<refsect1>
<title>Commands</title>
<para>The following commands are understood by
<filename>systemd-readahead</filename>:</para> <variablelist>
<varlistentry>
<term><command>collect
[<replaceable>DIRECTORY</replaceable>]</command></term>
<listitem>
<para>Collect read-ahead data on
early boot. When terminating it will
write out a pack file to the indicated
directory containing the read-ahead
data. </para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>replay
[<replaceable>DIRECTORY</replaceable>]</command></term>
<listitem>
<para>Perform read-ahead on the
specified directory tree.</para>
</listitem>
</varlistentry>
<varlistentry>
<term><command>analyze
[<replaceable>FILE</replaceable>]</command></term>
<listitem>
<para>Dumps the content of the
read-ahead pack file to the
terminal. The output lists
approximately for each file
how much will be read-ahead by
the <command>replay</command>
command.</para>
</listitem>
</varlistentry>
</variablelist>
</refsect1>
man: document the readahead services
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<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
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