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The new 'unique' API allows listing all unique field values that a field specified by a field name can take in all entries of the journal. This allows answering queries such as "What units logged to the journal?", "What hosts have logged into the journal?", "Which boot IDs have logged into the journal?". Ultimately this allows implementation of tools similar to lastlog based on journal data. Note that listing these field values will not work for journal files created with older journald, as the field values are not indexed in older files.
202 lines
9.6 KiB
XML
202 lines
9.6 KiB
XML
<?xml version='1.0'?> <!--*-nxml-*-->
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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
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"http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<!--
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This file is part of systemd.
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Copyright 2012 Lennart Poettering
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systemd is free software; you can redistribute it and/or modify it
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under the terms of the GNU Lesser General Public License as published by
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the Free Software Foundation; either version 2.1 of the License, or
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(at your option) any later version.
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systemd is distributed in the hope that it will be useful, but
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WITHOUT ANY WARRANTY; without even the implied warranty of
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MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU
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Lesser General Public License for more details.
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You should have received a copy of the GNU Lesser General Public License
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along with systemd; If not, see <http://www.gnu.org/licenses/>.
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-->
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<refentry id="sd_journal_get_data">
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<refentryinfo>
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<title>sd_journal_get_data</title>
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<productname>systemd</productname>
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<authorgroup>
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<author>
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<contrib>Developer</contrib>
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<firstname>Lennart</firstname>
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<surname>Poettering</surname>
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<email>lennart@poettering.net</email>
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</author>
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</authorgroup>
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</refentryinfo>
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<refmeta>
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<refentrytitle>sd_journal_get_data</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_get_data</refname>
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<refname>sd_journal_enumerate_data</refname>
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<refname>sd_journal_restart_data</refname>
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<refname>SD_JOURNAL_FOREACH_DATA</refname>
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<refpurpose>Read data fields from the current journal entry</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_get_data</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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<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_data</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_data</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_DATA</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_get_data()</function> gets
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the data object associated with a specific field from
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the current journal entry. It takes four arguments:
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the journal context object, a string with the field
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name to request, plus a pair of pointers to
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pointer/size variables where the data object and its
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size shall be stored in. The field name should be an
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entry field name. Well-known field names are listed in
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<citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>. The
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returned data is in a read-only memory map and is only
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valid until the next invocation of
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<function>sd_journal_get_data()</function> or
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<function>sd_journal_enumerate_data()</function>, or
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the read pointer is altered. Note that the data
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returned will be prefixed with the field name and
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'='.</para>
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<para><function>sd_journal_enumerate_data()</function>
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may be used to iterate through all fields of the
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current entry. On each invocation the data for the
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next field is returned. The order of these fields is
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not defined. The data returned is in the same format
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as with <function>sd_journal_get_data()</function> and
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also follows the same life-time semantics.</para>
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<para><function>sd_journal_restart_data()</function>
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resets the data enumeration index to the beginning of
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the entry. The next invocation of
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<function>sd_journal_enumerate_data()</function> will return the first
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field of the entry again.</para>
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<para>Note that the
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<function>SD_JOURNAL_FOREACH_DATA()</function> macro
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may be used as a handy wrapper around
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<function>sd_journal_restart_data()</function> and
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<function>sd_journal_enumerate_data()</function>.</para>
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<para>Note that these functions will not work before
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<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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(or related call) has been called at least
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once, in order to position the read pointer at a valid entry.</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_get_data()</function>
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returns 0 on success or a negative errno-style error
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code. If the current entry does not include the
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specified field -ENOENT is returned. If
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<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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has not been called at least once -EADDRNOTAVAIL is
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returned. <function>sd_journal_enumerate_data()</function>
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returns a positive integer if the next field has been
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read, 0 when no more fields are known, or a negative
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errno-style error
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code. <function>sd_journal_restart_data()</function>
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returns nothing.</para>
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</refsect1>
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<refsect1>
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<title>Notes</title>
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<para>The <function>sd_journal_get_data()</function>,
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<function>sd_journal_enumerate_data()</function> and
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<function>sd_journal_restart_data()</function>
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interfaces are available as shared library, which can
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be compiled and linked to with the
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<literal>libsystemd-journal</literal>
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<citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
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file.</para>
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</refsect1>
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<refsect1>
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<title>Examples</title>
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<para>See
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<citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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for a complete example how to use
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<function>sd_journal_get_data()</function>.</para>
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<para>Use the
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<function>SD_JOURNAL_FOREACH_DATA</function> macro to
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iterate through all fields of the current journal
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entry:</para>
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<programlisting>...
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int print_fields(sd_journal *j) {
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const void *data;
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size_t l;
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SD_JOURNAL_FOREACH_DATA(j, data, length)
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printf("%.*s\n", (int) length, data);
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}
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...</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_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_journal_get_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
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<citerefentry><refentrytitle>sd_journal_query_unique</refentrytitle><manvolnum>3</manvolnum></citerefentry>
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</para>
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</refsect1>
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</refentry>
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