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67c3cf4f | 1 | <?xml version='1.0'?> <!--*-nxml-*--> |
3a54a157 | 2 | <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN" |
eea10b26 | 3 | "http://www.oasis-open.org/docbook/xml/4.5/docbookx.dtd"> |
db9ecf05 | 4 | <!-- SPDX-License-Identifier: LGPL-2.1-or-later --> |
67c3cf4f | 5 | |
7d6b2723 | 6 | <refentry id="sd_journal_next" xmlns:xi="http://www.w3.org/2001/XInclude"> |
67c3cf4f | 7 | |
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8 | <refentryinfo> |
9 | <title>sd_journal_next</title> | |
10 | <productname>systemd</productname> | |
798d3a52 ZJS |
11 | </refentryinfo> |
12 | ||
13 | <refmeta> | |
14 | <refentrytitle>sd_journal_next</refentrytitle> | |
15 | <manvolnum>3</manvolnum> | |
16 | </refmeta> | |
17 | ||
18 | <refnamediv> | |
19 | <refname>sd_journal_next</refname> | |
20 | <refname>sd_journal_previous</refname> | |
b78f9481 | 21 | <refname>sd_journal_step_one</refname> |
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22 | <refname>sd_journal_next_skip</refname> |
23 | <refname>sd_journal_previous_skip</refname> | |
24 | <refname>SD_JOURNAL_FOREACH</refname> | |
25 | <refname>SD_JOURNAL_FOREACH_BACKWARDS</refname> | |
26 | <refpurpose>Advance or set back the read pointer in the journal</refpurpose> | |
27 | </refnamediv> | |
28 | ||
29 | <refsynopsisdiv> | |
30 | <funcsynopsis> | |
31 | <funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo> | |
32 | ||
33 | <funcprototype> | |
34 | <funcdef>int <function>sd_journal_next</function></funcdef> | |
35 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
36 | </funcprototype> | |
37 | ||
38 | <funcprototype> | |
39 | <funcdef>int <function>sd_journal_previous</function></funcdef> | |
40 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
41 | </funcprototype> | |
42 | ||
b78f9481 YW |
43 | <funcprototype> |
44 | <funcdef>int <function>sd_journal_step_one</function></funcdef> | |
45 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
46 | <paramdef>int <parameter>advanced</parameter></paramdef> | |
47 | </funcprototype> | |
48 | ||
798d3a52 ZJS |
49 | <funcprototype> |
50 | <funcdef>int <function>sd_journal_next_skip</function></funcdef> | |
51 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
52 | <paramdef>uint64_t <parameter>skip</parameter></paramdef> | |
53 | </funcprototype> | |
54 | ||
55 | <funcprototype> | |
56 | <funcdef>int <function>sd_journal_previous_skip</function></funcdef> | |
57 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
58 | <paramdef>uint64_t <parameter>skip</parameter></paramdef> | |
59 | </funcprototype> | |
60 | ||
61 | <funcprototype> | |
62 | <funcdef><function>SD_JOURNAL_FOREACH</function></funcdef> | |
63 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
64 | </funcprototype> | |
65 | ||
66 | <funcprototype> | |
67 | <funcdef><function>SD_JOURNAL_FOREACH_BACKWARDS</function></funcdef> | |
68 | <paramdef>sd_journal *<parameter>j</parameter></paramdef> | |
69 | </funcprototype> | |
70 | </funcsynopsis> | |
71 | </refsynopsisdiv> | |
72 | ||
73 | <refsect1> | |
74 | <title>Description</title> | |
75 | ||
76 | <para><function>sd_journal_next()</function> advances the read | |
77 | pointer into the journal by one entry. The only argument taken is | |
78 | a journal context object as allocated via | |
79 | <citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>. | |
80 | After successful invocation the entry may be read with functions | |
81 | such as | |
82 | <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> | |
83 | ||
84 | <para>Similarly, <function>sd_journal_previous()</function> sets | |
85 | the read pointer back one entry.</para> | |
86 | ||
b78f9481 YW |
87 | <para><function>sd_journal_step_one()</function> also moves the read pointer. If the current location |
88 | is the head of the journal, e.g. when this is called following | |
89 | <function>sd_journal_seek_head()</function>, then this is equivalent to | |
90 | <function>sd_journal_next()</function>, and the argument <varname>advanced</varname> will be ignored. | |
9a27ef09 | 91 | Similarly, if the current location is the tail of the journal, e.g. when this is called following |
b78f9481 YW |
92 | <function>sd_journal_seek_tail()</function>, then this is equivalent to |
93 | <function>sd_journal_previous()</function>, and <varname>advanced</varname> will be ignored. Otherwise, | |
94 | this is equivalent to <function>sd_journal_next()</function> when <varname>advanced</varname> is | |
95 | non-zero, and <function>sd_journal_previous()</function> when <varname>advanced</varname> is zero.</para> | |
96 | ||
798d3a52 | 97 | <para><function>sd_journal_next_skip()</function> and |
41d544a1 YW |
98 | <function>sd_journal_previous_skip()</function> advance/set back the read pointer by multiple |
99 | entries at once, as specified in the <varname>skip</varname> parameter. The <varname>skip</varname> | |
a2968e83 | 100 | parameter must be less than or equal to 2147483647 (2³¹-1).</para> |
798d3a52 ZJS |
101 | |
102 | <para>The journal is strictly ordered by reception time, and hence | |
103 | advancing to the next entry guarantees that the entry then | |
104 | pointing to is later in time than then previous one, or has the | |
105 | same timestamp.</para> | |
106 | ||
107 | <para>Note that | |
108 | <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
109 | and related calls will fail unless | |
110 | <function>sd_journal_next()</function> has been invoked at least | |
111 | once in order to position the read pointer on a journal | |
112 | entry.</para> | |
113 | ||
114 | <para>Note that the <function>SD_JOURNAL_FOREACH()</function> | |
115 | macro may be used as a wrapper around | |
116 | <citerefentry><refentrytitle>sd_journal_seek_head</refentrytitle><manvolnum>3</manvolnum></citerefentry> | |
117 | and <function>sd_journal_next()</function> in order to make | |
118 | iterating through the journal easier. See below for an example. | |
119 | Similarly, <function>SD_JOURNAL_FOREACH_BACKWARDS()</function> may | |
120 | be used for iterating the journal in reverse order.</para> | |
121 | </refsect1> | |
122 | ||
123 | <refsect1> | |
124 | <title>Return Value</title> | |
125 | ||
126 | <para>The four calls return the number of entries advanced/set | |
127 | back on success or a negative errno-style error code. When the end | |
128 | or beginning of the journal is reached, a number smaller than | |
129 | requested is returned. More specifically, if | |
130 | <function>sd_journal_next()</function> or | |
131 | <function>sd_journal_previous()</function> reach the end/beginning | |
132 | of the journal they will return 0, instead of 1 when they are | |
133 | successful. This should be considered an EOF marker.</para> | |
134 | </refsect1> | |
135 | ||
136 | <refsect1> | |
137 | <title>Notes</title> | |
138 | ||
64a7ef8b | 139 | <xi:include href="threads-aware.xml" xpointer="strict"/> |
a8d46a16 | 140 | |
7d6b2723 | 141 | <xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/> |
798d3a52 ZJS |
142 | </refsect1> |
143 | ||
144 | <refsect1> | |
145 | <title>Examples</title> | |
146 | ||
147 | <para>Iterating through the journal:</para> | |
148 | ||
29c45dc4 | 149 | <programlisting><xi:include href="journal-iterate-foreach.c" parse="text" /></programlisting> |
798d3a52 | 150 | </refsect1> |
67c3cf4f | 151 | |
69106f47 AK |
152 | <refsect1> |
153 | <title>History</title> | |
00f95506 AK |
154 | <para><function>sd_journal_next()</function>, |
155 | <function>sd_journal_previous()</function>, | |
156 | <function>sd_journal_next_skip()</function>, | |
157 | <function>sd_journal_previous_skip()</function>, | |
158 | <function>SD_JOURNAL_FOREACH()</function>, and | |
159 | <function>SD_JOURNAL_FOREACH_BACKWARDS()</function> were added in version 187.</para> | |
69106f47 AK |
160 | <para><function>sd_journal_step_one()</function> was added in version 254.</para> |
161 | </refsect1> | |
162 | ||
798d3a52 ZJS |
163 | <refsect1> |
164 | <title>See Also</title> | |
67c3cf4f | 165 | |
13a69c12 DT |
166 | <para><simplelist type="inline"> |
167 | <member><citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry></member> | |
168 | <member><citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry></member> | |
169 | <member><citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry></member> | |
170 | <member><citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry></member> | |
171 | <member><citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry></member> | |
172 | <member><citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry></member> | |
173 | </simplelist></para> | |
798d3a52 | 174 | </refsect1> |
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175 | |
176 | </refentry> |