1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
59
60
61
62
63
64
65
66
67
68
69
70
71
72
73
74
75
76
77
78
79
80
81
82
83
84
85
86
87
88
89
90
91
92
93
94
95
96
97
98
99
100
101
102
103
104
105
106
107
108
109
110
111
112
113
114
115
116
117
118
119
120
121
122
123
124
125
126
127
128
129
130
131
132
133
134
135
136
137
138
139
140
141
142
143
144
145
146
147
148
149
150
151
152
153
154
155
156
157
158
159
160
161
162
163
164
165
166
167
168
169
170
171
172
173
174
175
|
<?xml version='1.0'?> <!--*-nxml-*-->
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
<refentry id="sd_journal_next" xmlns:xi="http://www.w3.org/2001/XInclude">
<refentryinfo>
<title>sd_journal_next</title>
<productname>systemd</productname>
</refentryinfo>
<refmeta>
<refentrytitle>sd_journal_next</refentrytitle>
<manvolnum>3</manvolnum>
</refmeta>
<refnamediv>
<refname>sd_journal_next</refname>
<refname>sd_journal_previous</refname>
<refname>sd_journal_next_skip</refname>
<refname>sd_journal_previous_skip</refname>
<refname>SD_JOURNAL_FOREACH</refname>
<refname>SD_JOURNAL_FOREACH_BACKWARDS</refname>
<refpurpose>Advance or set back the read pointer in the journal</refpurpose>
</refnamediv>
<refsynopsisdiv>
<funcsynopsis>
<funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo>
<funcprototype>
<funcdef>int <function>sd_journal_next</function></funcdef>
<paramdef>sd_journal *<parameter>j</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_journal_previous</function></funcdef>
<paramdef>sd_journal *<parameter>j</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_journal_next_skip</function></funcdef>
<paramdef>sd_journal *<parameter>j</parameter></paramdef>
<paramdef>uint64_t <parameter>skip</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef>int <function>sd_journal_previous_skip</function></funcdef>
<paramdef>sd_journal *<parameter>j</parameter></paramdef>
<paramdef>uint64_t <parameter>skip</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef><function>SD_JOURNAL_FOREACH</function></funcdef>
<paramdef>sd_journal *<parameter>j</parameter></paramdef>
</funcprototype>
<funcprototype>
<funcdef><function>SD_JOURNAL_FOREACH_BACKWARDS</function></funcdef>
<paramdef>sd_journal *<parameter>j</parameter></paramdef>
</funcprototype>
</funcsynopsis>
</refsynopsisdiv>
<refsect1>
<title>Description</title>
<para><function>sd_journal_next()</function> advances the read
pointer into the journal by one entry. The only argument taken is
a journal context object as allocated via
<citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>.
After successful invocation the entry may be read with functions
such as
<citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para>
<para>Similarly, <function>sd_journal_previous()</function> sets
the read pointer back one entry.</para>
<para><function>sd_journal_next_skip()</function> and
<function>sd_journal_previous_skip()</function> advance/set back the read pointer by multiple
entries at once, as specified in the <varname>skip</varname> parameter. The <varname>skip</varname>
parameter must be less than or equal to 2147483647 (2^31-1).</para>
<para>The journal is strictly ordered by reception time, and hence
advancing to the next entry guarantees that the entry then
pointing to is later in time than then previous one, or has the
same timestamp.</para>
<para>Note that
<citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>
and related calls will fail unless
<function>sd_journal_next()</function> has been invoked at least
once in order to position the read pointer on a journal
entry.</para>
<para>Note that the <function>SD_JOURNAL_FOREACH()</function>
macro may be used as a wrapper around
<citerefentry><refentrytitle>sd_journal_seek_head</refentrytitle><manvolnum>3</manvolnum></citerefentry>
and <function>sd_journal_next()</function> in order to make
iterating through the journal easier. See below for an example.
Similarly, <function>SD_JOURNAL_FOREACH_BACKWARDS()</function> may
be used for iterating the journal in reverse order.</para>
</refsect1>
<refsect1>
<title>Return Value</title>
<para>The four calls return the number of entries advanced/set
back on success or a negative errno-style error code. When the end
or beginning of the journal is reached, a number smaller than
requested is returned. More specifically, if
<function>sd_journal_next()</function> or
<function>sd_journal_previous()</function> reach the end/beginning
of the journal they will return 0, instead of 1 when they are
successful. This should be considered an EOF marker.</para>
</refsect1>
<refsect1>
<title>Notes</title>
<xi:include href="threads-aware.xml" xpointer="strict"/>
<xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
</refsect1>
<refsect1>
<title>Examples</title>
<para>Iterating through the journal:</para>
<programlisting>#include <stdio.h>
#include <string.h>
#include <systemd/sd-journal.h>
int main(int argc, char *argv[]) {
int r;
sd_journal *j;
r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY);
if (r < 0) {
fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
return 1;
}
SD_JOURNAL_FOREACH(j) {
const char *d;
size_t l;
r = sd_journal_get_data(j, "MESSAGE", (const void **)&d, &l);
if (r < 0) {
fprintf(stderr, "Failed to read message field: %s\n", strerror(-r));
continue;
}
printf("%.*s\n", (int) l, d);
}
sd_journal_close(j);
return 0;
}</programlisting>
</refsect1>
<refsect1>
<title>See Also</title>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
<citerefentry><refentrytitle>sd_journal_get_cursor</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>
</refentry>
|
