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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 2012 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="sd_journal_next"> | |
25 | ||
26 | <refentryinfo> | |
27 | <title>sd_journal_next</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>sd_journal_next</refentrytitle> | |
42 | <manvolnum>3</manvolnum> | |
43 | </refmeta> | |
44 | ||
45 | <refnamediv> | |
46 | <refname>sd_journal_next</refname> | |
47 | <refname>sd_journal_previous</refname> | |
48 | <refname>sd_journal_next_skip</refname> | |
49 | <refname>sd_journal_previous_skip</refname> | |
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50 | <refname>SD_JOURNAL_FOREACH</refname> |
51 | <refname>SD_JOURNAL_FOREACH_BACKWARDS</refname> | |
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52 | <refpurpose>Advance or set back the read pointer in the journal</refpurpose> |
53 | </refnamediv> | |
54 | ||
55 | <refsynopsisdiv> | |
56 | <funcsynopsis> | |
57 | <funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo> | |
58 | ||
59 | <funcprototype> | |
60 | <funcdef>int <function>sd_journal_next</function></funcdef> | |
61 | <paramdef>sd_journal* <parameter>j</parameter></paramdef> | |
62 | </funcprototype> | |
63 | ||
64 | <funcprototype> | |
65 | <funcdef>int <function>sd_journal_previous</function></funcdef> | |
66 | <paramdef>sd_journal* <parameter>j</parameter></paramdef> | |
67 | </funcprototype> | |
68 | ||
69 | <funcprototype> | |
70 | <funcdef>int <function>sd_journal_next_skip</function></funcdef> | |
71 | <paramdef>sd_journal* <parameter>j</parameter></paramdef> | |
72 | <paramdef>uint64_t <parameter>skip</parameter></paramdef> | |
73 | </funcprototype> | |
74 | ||
75 | <funcprototype> | |
76 | <funcdef>int <function>sd_journal_previous_skip</function></funcdef> | |
77 | <paramdef>sd_journal* <parameter>j</parameter></paramdef> | |
78 | <paramdef>uint64_t <parameter>skip</parameter></paramdef> | |
79 | </funcprototype> | |
80 | ||
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81 | <funcprototype> |
82 | <funcdef><function>SD_JOURNAL_FOREACH</function></funcdef> | |
83 | <paramdef>sd_journal* <parameter>j</parameter></paramdef> | |
84 | </funcprototype> | |
85 | ||
86 | <funcprototype> | |
87 | <funcdef><function>SD_JOURNAL_FOREACH_BACKWARDS</function></funcdef> | |
88 | <paramdef>sd_journal* <parameter>j</parameter></paramdef> | |
89 | </funcprototype> | |
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90 | </funcsynopsis> |
91 | </refsynopsisdiv> | |
92 | ||
93 | <refsect1> | |
94 | <title>Description</title> | |
95 | ||
96 | <para><function>sd_journal_next()</function> advances | |
97 | the read pointer into the journal by one entry. The | |
98 | only argument taken is a journal context object as | |
99 | allocated via | |
100 | <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>. After | |
101 | successful invocation the entry may be read with | |
102 | functions such as | |
103 | <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> | |
104 | ||
105 | <para>Similar, <function>sd_journal_previous()</function> sets | |
106 | the read pointer back one entry.</para> | |
107 | ||
108 | <para><function>sd_journal_next_skip()</function> and | |
109 | <function>sd_journal_previous_skip()</function> | |
110 | advance/set back the read pointer by multiple entries | |
111 | at once, as specified in the <varname>skip</varname> | |
112 | parameter.</para> | |
113 | ||
114 | <para>The journal is strictly ordered by reception | |
115 | time, and hence advancing to the next entry guarantees | |
116 | that the entry then pointing to is later in time than | |
117 | then previous one, or has the same timestamp.</para> | |
118 | ||
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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 | |
123 | invoked at least once in order to position the read | |
124 | pointer on a journal entry.</para> | |
125 | ||
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126 | <para>Note that the |
127 | <function>SD_JOURNAL_FOREACH()</function> macro may be used | |
128 | as a wrapper around | |
129 | <citerefentry><refentrytitle>sd_journal_seek_head</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
130 | and <function>sd_journal_next()</function> in order to | |
bb31a4ac | 131 | make iterating through the journal easier. See below |
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132 | for an example. Similar, |
133 | <function>SD_JOURNAL_FOREACH_BACKWARDS()</function> | |
134 | may be used for iterating the journal in reverse | |
135 | order.</para> | |
136 | </refsect1> | |
137 | ||
138 | <refsect1> | |
139 | <title>Return Value</title> | |
140 | ||
141 | <para>The four calls return the number of entries | |
142 | advanced/set back on success or a negative errno-style | |
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143 | error code. When the end or beginning of the journal |
144 | is reached, a number smaller than requested is | |
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145 | returned. More specifically, if |
146 | <function>sd_journal_next()</function> or | |
147 | <function>sd_journal_previous()</function> reach the | |
148 | end/beginning of the journal they will return 0, | |
149 | instead of 1 when they are successful. This should be | |
150 | considered an EOF marker.</para> | |
151 | </refsect1> | |
152 | ||
153 | <refsect1> | |
154 | <title>Notes</title> | |
155 | ||
156 | <para>The <function>sd_journal_next()</function>, <function>sd_journal_previous()</function>, | |
157 | <function>sd_journal_next_skip()</function> and | |
158 | <function>sd_journal_previous_skip()</function> interfaces are | |
159 | available as shared library, which can be compiled and | |
160 | linked to with the | |
1e158d27 | 161 | <constant>libsystemd-journal</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> |
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162 | file.</para> |
163 | </refsect1> | |
164 | ||
165 | <refsect1> | |
166 | <title>Examples</title> | |
167 | ||
168 | <para>Iterating through the journal:</para> | |
169 | ||
170 | <programlisting>#include <stdio.h> | |
171 | #include <string.h> | |
172 | #include <systemd/sd-journal.h> | |
173 | ||
174 | int main(int argc, char *argv[]) { | |
175 | int r; | |
176 | sd_journal *j; | |
177 | r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY); | |
178 | if (r < 0) { | |
179 | fprintf(stderr, "Failed to open journal: %s\n", strerror(-r)); | |
180 | return 1; | |
181 | } | |
182 | SD_JOURNAL_FOREACH(j) { | |
183 | const char *d; | |
184 | size_t l; | |
185 | ||
186 | r = sd_journal_get_data(j, "MESSAGE", &d, &l); | |
187 | if (r < 0) { | |
188 | fprintf(stderr, "Failed to read message field: %s\n", strerror(-r)); | |
189 | continue; | |
190 | } | |
191 | ||
192 | printf("%.*s\n", (int) l, d); | |
193 | } | |
194 | sd_journal_close(j); | |
195 | return 0; | |
196 | }</programlisting> | |
197 | ||
198 | </refsect1> | |
199 | ||
200 | <refsect1> | |
201 | <title>See Also</title> | |
202 | ||
203 | <para> | |
204 | <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, | |
205 | <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
206 | <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
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207 | <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>, |
208 | <citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>, | |
209 | <citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
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210 | </para> |
211 | </refsect1> | |
212 | ||
213 | </refentry> |