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176 lines
8.4 KiB
XML
176 lines
8.4 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.5//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!-- SPDX-License-Identifier: LGPL-2.1-or-later -->
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<refentry id="sd_journal_query_unique" xmlns:xi="http://www.w3.org/2001/XInclude">
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<refentryinfo>
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<title>sd_journal_query_unique</title>
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<productname>systemd</productname>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_journal_query_unique</refentrytitle>
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<manvolnum>3</manvolnum>
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</refmeta>
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<refnamediv>
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<refname>sd_journal_query_unique</refname>
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<refname>sd_journal_enumerate_unique</refname>
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<refname>sd_journal_enumerate_available_unique</refname>
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<refname>sd_journal_restart_unique</refname>
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<refname>SD_JOURNAL_FOREACH_UNIQUE</refname>
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<refpurpose>Read unique data fields from the journal</refpurpose>
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</refnamediv>
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<refsynopsisdiv>
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<funcsynopsis>
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<funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo>
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<funcprototype>
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<funcdef>int <function>sd_journal_query_unique</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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<paramdef>const char *<parameter>field</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_journal_enumerate_available_unique</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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<paramdef>const void **<parameter>data</parameter></paramdef>
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<paramdef>size_t *<parameter>length</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>int <function>sd_journal_enumerate_unique</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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<paramdef>const void **<parameter>data</parameter></paramdef>
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<paramdef>size_t *<parameter>length</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef>void <function>sd_journal_restart_unique</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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</funcprototype>
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<funcprototype>
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<funcdef><function>SD_JOURNAL_FOREACH_UNIQUE</function></funcdef>
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<paramdef>sd_journal *<parameter>j</parameter></paramdef>
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<paramdef>const void *<parameter>data</parameter></paramdef>
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<paramdef>size_t <parameter>length</parameter></paramdef>
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</funcprototype>
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</funcsynopsis>
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</refsynopsisdiv>
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<refsect1>
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<title>Description</title>
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<para><function>sd_journal_query_unique()</function> queries the journal for all unique values the
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specified field can take. It takes two arguments: the journal to query and the field name to look
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for. Well-known field names are listed on
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<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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but any field can be specified. Field names must be specified without a trailing
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<literal>=</literal>. After this function has been executed successfully the field values may be queried
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using <function>sd_journal_enumerate_unique()</function> and
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<function>sd_journal_enumerate_available_unique()</function>. Invoking one of those calls will change the
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field name being queried and reset the enumeration index to the first field value that matches.</para>
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<para><function>sd_journal_enumerate_unique()</function> may be used to iterate through all data fields
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which match the previously selected field name as set with
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<function>sd_journal_query_unique()</function>. On each invocation the next field data matching the field
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name is returned. The order of the returned data fields is not defined. It takes three arguments: the
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journal object, plus a pair of pointers to pointer/size variables where the data object and its size
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shall be stored. The returned data is in a read-only memory map and is only valid until the next
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invocation of <function>sd_journal_enumerate_unique()</function>. Note that the data returned will be
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prefixed with the field name and <literal>=</literal>. Note that this call is subject to the data field
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size threshold as controlled by <function>sd_journal_set_data_threshold()</function> and only the initial
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part of the field up to the threshold is returned. An error is returned for fields which cannot be
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retrieved. See the error list below for details.</para>
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<para><function>sd_journal_enumerate_available_unique()</function> is similar to
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<function>sd_journal_enumerate_unique()</function>, but silently skips any fields which may be valid, but
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are too large or not supported by current implementation.</para>
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<para><function>sd_journal_restart_unique()</function> resets the
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data enumeration index to the beginning of the list. The next
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invocation of <function>sd_journal_enumerate_unique()</function>
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will return the first field data matching the field name
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again.</para>
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<para>Note that the <function>SD_JOURNAL_FOREACH_UNIQUE()</function> macro may be used as a handy wrapper
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around <function>sd_journal_restart_unique()</function> and
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<function>sd_journal_enumerate_available_unique()</function>.</para>
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<para>Note that these functions currently are not influenced by
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matches set with <function>sd_journal_add_match()</function> but
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this might change in a later version of this software.</para>
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<para>To enumerate all field names currently in use (and thus all suitable field parameters for
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<function>sd_journal_query_unique()</function>), use the
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<citerefentry><refentrytitle>sd_journal_enumerate_fields</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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call.</para>
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</refsect1>
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<refsect1>
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<title>Return Value</title>
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<para><function>sd_journal_query_unique()</function> returns 0 on success or a negative errno-style error
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code. <function>sd_journal_enumerate_unique()</function> and
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<function>sd_journal_query_available_unique()</function> return a positive integer if the next field data
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has been read, 0 when no more fields remain, or a negative errno-style error code.
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<function>sd_journal_restart_unique()</function> doesn't return anything.</para>
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<refsect2>
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<title>Errors</title>
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<para>Returned errors may indicate the following problems:</para>
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<variablelist>
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<xi:include href="sd_journal_get_data.xml" xpointer="EINVAL"/>
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<xi:include href="sd_journal_get_data.xml" xpointer="ECHILD"/>
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<xi:include href="sd_journal_get_data.xml" xpointer="EADDRNOTAVAIL"/>
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<xi:include href="sd_journal_get_data.xml" xpointer="ENOENT"/>
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<xi:include href="sd_journal_get_data.xml" xpointer="ENOBUFS"/>
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<xi:include href="sd_journal_get_data.xml" xpointer="E2BIG"/>
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<xi:include href="sd_journal_get_data.xml" xpointer="EPROTONOSUPPORT"/>
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<xi:include href="sd_journal_get_data.xml" xpointer="EBADMSG"/>
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<xi:include href="sd_journal_get_data.xml" xpointer="EIO"/>
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</variablelist>
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</refsect2>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<xi:include href="threads-aware.xml" xpointer="strict"/>
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<xi:include href="libsystemd-pkgconfig.xml" xpointer="pkgconfig-text"/>
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</refsect1>
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<refsect1>
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<title>Examples</title>
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<para>Use the <function>SD_JOURNAL_FOREACH_UNIQUE()</function> macro to iterate through all values a field
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of the journal can take (and which can be accessed on the given architecture and are not compressed with
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an unsupported mechanism). The following example lists all unit names referenced in the journal:</para>
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<programlisting><xi:include href="journal-iterate-unique.c" parse="text" /></programlisting>
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</refsect1>
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<refsect1>
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<title>See Also</title>
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<para>
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<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_journal_open</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_journal_enumerate_fields</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_journal_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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