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1 | <?xml version='1.0'?> <!--*-nxml-*--> |
2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" | |
12b42c76 | 3 | "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> |
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4 | |
5 | <!-- | |
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6 | SPDX-License-Identifier: LGPL-2.1+ |
7 | ||
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8 | This file is part of systemd. |
9 | ||
10 | Copyright 2012 Lennart Poettering | |
11 | ||
12 | systemd is free software; you can redistribute it and/or modify it | |
13 | under the terms of the GNU Lesser General Public License as published by | |
14 | the Free Software Foundation; either version 2.1 of the License, or | |
15 | (at your option) any later version. | |
16 | ||
17 | systemd is distributed in the hope that it will be useful, but | |
18 | WITHOUT ANY WARRANTY; without even the implied warranty of | |
19 | MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU | |
20 | Lesser General Public License for more details. | |
21 | ||
22 | You should have received a copy of the GNU Lesser General Public License | |
23 | along with systemd; If not, see <http://www.gnu.org/licenses/>. | |
24 | --> | |
25 | ||
26 | <refentry id="sd_journal_next"> | |
27 | ||
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28 | <refentryinfo> |
29 | <title>sd_journal_next</title> | |
30 | <productname>systemd</productname> | |
31 | ||
32 | <authorgroup> | |
33 | <author> | |
34 | <contrib>Developer</contrib> | |
35 | <firstname>Lennart</firstname> | |
36 | <surname>Poettering</surname> | |
37 | <email>lennart@poettering.net</email> | |
38 | </author> | |
39 | </authorgroup> | |
40 | </refentryinfo> | |
41 | ||
42 | <refmeta> | |
43 | <refentrytitle>sd_journal_next</refentrytitle> | |
44 | <manvolnum>3</manvolnum> | |
45 | </refmeta> | |
46 | ||
47 | <refnamediv> | |
48 | <refname>sd_journal_next</refname> | |
49 | <refname>sd_journal_previous</refname> | |
50 | <refname>sd_journal_next_skip</refname> | |
51 | <refname>sd_journal_previous_skip</refname> | |
52 | <refname>SD_JOURNAL_FOREACH</refname> | |
53 | <refname>SD_JOURNAL_FOREACH_BACKWARDS</refname> | |
54 | <refpurpose>Advance or set back the read pointer in the journal</refpurpose> | |
55 | </refnamediv> | |
56 | ||
57 | <refsynopsisdiv> | |
58 | <funcsynopsis> | |
59 | <funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo> | |
60 | ||
61 | <funcprototype> | |
62 | <funcdef>int <function>sd_journal_next</function></funcdef> | |
63 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
64 | </funcprototype> | |
65 | ||
66 | <funcprototype> | |
67 | <funcdef>int <function>sd_journal_previous</function></funcdef> | |
68 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
69 | </funcprototype> | |
70 | ||
71 | <funcprototype> | |
72 | <funcdef>int <function>sd_journal_next_skip</function></funcdef> | |
73 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
74 | <paramdef>uint64_t <parameter>skip</parameter></paramdef> | |
75 | </funcprototype> | |
76 | ||
77 | <funcprototype> | |
78 | <funcdef>int <function>sd_journal_previous_skip</function></funcdef> | |
79 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
80 | <paramdef>uint64_t <parameter>skip</parameter></paramdef> | |
81 | </funcprototype> | |
82 | ||
83 | <funcprototype> | |
84 | <funcdef><function>SD_JOURNAL_FOREACH</function></funcdef> | |
85 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
86 | </funcprototype> | |
87 | ||
88 | <funcprototype> | |
89 | <funcdef><function>SD_JOURNAL_FOREACH_BACKWARDS</function></funcdef> | |
90 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
91 | </funcprototype> | |
92 | </funcsynopsis> | |
93 | </refsynopsisdiv> | |
94 | ||
95 | <refsect1> | |
96 | <title>Description</title> | |
97 | ||
98 | <para><function>sd_journal_next()</function> advances the read | |
99 | pointer into the journal by one entry. The only argument taken is | |
100 | a journal context object as allocated via | |
101 | <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>. | |
102 | After successful invocation the entry may be read with functions | |
103 | such as | |
104 | <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> | |
105 | ||
106 | <para>Similarly, <function>sd_journal_previous()</function> sets | |
107 | the read pointer back one entry.</para> | |
108 | ||
109 | <para><function>sd_journal_next_skip()</function> and | |
110 | <function>sd_journal_previous_skip()</function> advance/set back | |
111 | the read pointer by multiple entries at once, as specified in the | |
112 | <varname>skip</varname> parameter.</para> | |
113 | ||
114 | <para>The journal is strictly ordered by reception time, and hence | |
115 | advancing to the next entry guarantees that the entry then | |
116 | pointing to is later in time than then previous one, or has the | |
117 | same timestamp.</para> | |
118 | ||
119 | <para>Note that | |
120 | <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
121 | and related calls will fail unless | |
122 | <function>sd_journal_next()</function> has been invoked at least | |
123 | once in order to position the read pointer on a journal | |
124 | entry.</para> | |
125 | ||
126 | <para>Note that the <function>SD_JOURNAL_FOREACH()</function> | |
127 | macro may be used as a wrapper around | |
128 | <citerefentry><refentrytitle>sd_journal_seek_head</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
129 | and <function>sd_journal_next()</function> in order to make | |
130 | iterating through the journal easier. See below for an example. | |
131 | Similarly, <function>SD_JOURNAL_FOREACH_BACKWARDS()</function> may | |
132 | be used for iterating the journal in reverse order.</para> | |
133 | </refsect1> | |
134 | ||
135 | <refsect1> | |
136 | <title>Return Value</title> | |
137 | ||
138 | <para>The four calls return the number of entries advanced/set | |
139 | back on success or a negative errno-style error code. When the end | |
140 | or beginning of the journal is reached, a number smaller than | |
141 | requested is returned. More specifically, if | |
142 | <function>sd_journal_next()</function> or | |
143 | <function>sd_journal_previous()</function> reach the end/beginning | |
144 | of the journal they will return 0, instead of 1 when they are | |
145 | successful. This should be considered an EOF marker.</para> | |
146 | </refsect1> | |
147 | ||
148 | <refsect1> | |
149 | <title>Notes</title> | |
150 | ||
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151 | <para>All functions listed here are thread-agnostic and only a single thread may operate |
152 | on a given <structname>sd_journal</structname> object.</para> | |
153 | ||
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154 | <para>The <function>sd_journal_next()</function>, |
155 | <function>sd_journal_previous()</function>, | |
156 | <function>sd_journal_next_skip()</function> and | |
157 | <function>sd_journal_previous_skip()</function> interfaces are | |
158 | available as a shared library, which can be compiled and linked to | |
159 | with the | |
160 | <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> | |
161 | file.</para> | |
162 | </refsect1> | |
163 | ||
164 | <refsect1> | |
165 | <title>Examples</title> | |
166 | ||
167 | <para>Iterating through the journal:</para> | |
168 | ||
169 | <programlisting>#include <stdio.h> | |
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170 | #include <string.h> |
171 | #include <systemd/sd-journal.h> | |
172 | ||
173 | int main(int argc, char *argv[]) { | |
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174 | int r; |
175 | sd_journal *j; | |
176 | r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY); | |
177 | if (r < 0) { | |
178 | fprintf(stderr, "Failed to open journal: %s\n", strerror(-r)); | |
179 | return 1; | |
180 | } | |
181 | SD_JOURNAL_FOREACH(j) { | |
182 | const char *d; | |
183 | size_t l; | |
184 | ||
185 | r = sd_journal_get_data(j, "MESSAGE", (const void **)&d, &l); | |
186 | if (r < 0) { | |
187 | fprintf(stderr, "Failed to read message field: %s\n", strerror(-r)); | |
188 | continue; | |
189 | } | |
190 | ||
191 | printf("%.*s\n", (int) l, d); | |
192 | } | |
193 | sd_journal_close(j); | |
194 | return 0; | |
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195 | }</programlisting> |
196 | ||
798d3a52 | 197 | </refsect1> |
67c3cf4f | 198 | |
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199 | <refsect1> |
200 | <title>See Also</title> | |
67c3cf4f | 201 | |
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202 | <para> |
203 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
204 | <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
205 | <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
206 | <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
207 | <citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
208 | <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
209 | </para> | |
210 | </refsect1> | |
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211 | |
212 | </refentry> |