mirror of
https://github.com/systemd/systemd
synced 2024-09-06 16:56:43 +00:00
![Lennart Poettering](/assets/img/avatar_default.png)
These lines are generally out-of-date, incomplete and unnecessary. With SPDX and git repository much more accurate and fine grained information about licensing and authorship is available, hence let's drop the per-file copyright notice. Of course, removing copyright lines of others is problematic, hence this commit only removes my own lines and leaves all others untouched. It might be nicer if sooner or later those could go away too, making git the only and accurate source of authorship information.
189 lines
6.7 KiB
XML
189 lines
6.7 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
|
|
<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
|
|
"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
|
|
|
|
<!--
|
|
SPDX-License-Identifier: LGPL-2.1+
|
|
-->
|
|
|
|
<refentry id="sd_journal_next" xmlns:xi="http://www.w3.org/2001/XInclude">
|
|
|
|
<refentryinfo>
|
|
<title>sd_journal_next</title>
|
|
<productname>systemd</productname>
|
|
|
|
<authorgroup>
|
|
<author>
|
|
<contrib>Developer</contrib>
|
|
<firstname>Lennart</firstname>
|
|
<surname>Poettering</surname>
|
|
<email>lennart@poettering.net</email>
|
|
</author>
|
|
</authorgroup>
|
|
</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.</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>
|
|
|
|
<para>All functions listed here are thread-agnostic and only a single thread may operate
|
|
on a given <structname>sd_journal</structname> object.</para>
|
|
|
|
<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>
|