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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 | ||
5 | <!-- | |
6 | This file is part of systemd. | |
7 | ||
8 | Copyright 2010 Lennart Poettering | |
9 | ||
10 | systemd is free software; you can redistribute it and/or modify it | |
11 | under the terms of the GNU Lesser General Public License as published by | |
12 | the Free Software Foundation; either version 2.1 of the License, or | |
13 | (at your option) any later version. | |
14 | ||
15 | systemd is distributed in the hope that it will be useful, but | |
16 | WITHOUT ANY WARRANTY; without even the implied warranty of | |
17 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
18 | Lesser General Public License for more details. | |
19 | ||
20 | You should have received a copy of the GNU Lesser General Public License | |
21 | along with systemd; If not, see <http://www.gnu.org/licenses/>. | |
22 | --> | |
23 | ||
24 | <refentry id="systemd-readahead-replay.service"> | |
25 | ||
26 | <refentryinfo> | |
27 | <title>systemd-readahead-replay.service</title> | |
28 | <productname>systemd</productname> | |
29 | ||
30 | <authorgroup> | |
31 | <author> | |
32 | <contrib>Developer</contrib> | |
33 | <firstname>Lennart</firstname> | |
34 | <surname>Poettering</surname> | |
35 | <email>lennart@poettering.net</email> | |
36 | </author> | |
37 | </authorgroup> | |
38 | </refentryinfo> | |
39 | ||
40 | <refmeta> | |
41 | <refentrytitle>systemd-readahead-replay.service</refentrytitle> | |
42 | <manvolnum>8</manvolnum> | |
43 | </refmeta> | |
44 | ||
45 | <refnamediv> | |
46 | <refname>systemd-readahead-replay.service</refname> | |
47 | <refname>systemd-readahead-collect.service</refname> | |
48 | <refname>systemd-readahead-done.service</refname> | |
49 | <refname>systemd-readahead-done.timer</refname> | |
50 | <refname>systemd-readahead</refname> | |
51 | <refpurpose>systemd Disk Read Ahead Logic</refpurpose> | |
52 | </refnamediv> | |
53 | ||
54 | <refsynopsisdiv> | |
55 | <para><filename>systemd-readahead-replay.service</filename></para> | |
56 | <para><filename>systemd-readahead-collect.service</filename></para> | |
57 | <para><filename>systemd-readahead-done.service</filename></para> | |
58 | <para><filename>systemd-readahead-done.timer</filename></para> | |
59 | <para><filename>/usr/lib/systemd/systemd-readahead</filename></para> | |
60 | </refsynopsisdiv> | |
61 | ||
62 | <refsect1> | |
63 | <title>Description</title> | |
64 | ||
65 | <para><filename>systemd-readahead-collect.service</filename> | |
66 | is a service that collects disk usage patterns at boot | |
67 | time. <filename>systemd-readahead-replay.service</filename> | |
68 | is a service that replays this access data collected | |
69 | at the subsequent boot. Since disks tend to be | |
70 | magnitudes slower than RAM this is intended to improve | |
71 | boot speeds by pre-loading early at boot all data on | |
72 | disk that is known to be read for the complete boot | |
73 | process.</para> | |
74 | ||
75 | <para><filename>systemd-readahead-done.service</filename> | |
76 | is executed a short while after boot completed and signals | |
77 | <filename>systemd-readahead-collect.service</filename> | |
78 | to end data collection. On this signal this service | |
79 | will then sort the collected disk accesses and store | |
80 | information about them disk in | |
81 | <filename>/.readahead</filename>.</para> | |
82 | ||
83 | <para>Normally, both | |
84 | <filename>systemd-readahead-collect.service</filename> | |
85 | and | |
86 | <filename>systemd-readahead-replay.service</filename> | |
87 | are activated at boot so that access patterns from the | |
88 | preceeding boot are replayed and new data collected | |
89 | for the subsequent boot. However, on read-only media | |
90 | where the collected data cannot be stored it might | |
91 | be a good idea to disable | |
92 | <filename>systemd-readahead-collect.service</filename>.</para> | |
93 | ||
94 | <para>On rotating media, when replaying disk accesses | |
95 | at early boot | |
96 | <filename>systemd-readahead-replay.service</filename> | |
97 | will order read requests by their location on disk. On | |
98 | non-rotating media, they will be ordered by their | |
99 | original access timestamp. If the file system supports | |
100 | it | |
101 | <filename>systemd-readahead-collect.service</filename> | |
102 | will also defragment and rearrange files on disk to | |
103 | optimize subsequent boot times.</para> | |
104 | </refsect1> | |
105 | ||
106 | <refsect1> | |
107 | <title>See Also</title> | |
108 | <para> | |
109 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
110 | </para> | |
111 | </refsect1> | |
112 | ||
113 | </refentry> |