<?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"> <!-- This file is part of systemd. Copyright 2012 Lennart Poettering systemd is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. systemd is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with systemd; If not, see <http://www.gnu.org/licenses/>. --> <refentry id="sd_journal_query_unique"> <refentryinfo> <title>sd_journal_query_unique</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_query_unique</refentrytitle> <manvolnum>3</manvolnum> </refmeta> <refnamediv> <refname>sd_journal_query_unique</refname> <refname>sd_journal_enumerate_unique</refname> <refname>sd_journal_restart_unique</refname> <refname>SD_JOURNAL_FOREACH_UNIQUE</refname> <refpurpose>Read unique data fields from the journal</refpurpose> </refnamediv> <refsynopsisdiv> <funcsynopsis> <funcsynopsisinfo>#include <systemd/sd-journal.h></funcsynopsisinfo> <funcprototype> <funcdef>int <function>sd_journal_query_unique</function></funcdef> <paramdef>sd_journal *<parameter>j</parameter></paramdef> <paramdef>const char *<parameter>field</parameter></paramdef> </funcprototype> <funcprototype> <funcdef>int <function>sd_journal_enumerate_unique</function></funcdef> <paramdef>sd_journal *<parameter>j</parameter></paramdef> <paramdef>const void **<parameter>data</parameter></paramdef> <paramdef>size_t *<parameter>length</parameter></paramdef> </funcprototype> <funcprototype> <funcdef>void <function>sd_journal_restart_unique</function></funcdef> <paramdef>sd_journal *<parameter>j</parameter></paramdef> </funcprototype> <funcprototype> <funcdef><function>SD_JOURNAL_FOREACH_UNIQUE</function></funcdef> <paramdef>sd_journal *<parameter>j</parameter></paramdef> <paramdef>const void *<parameter>data</parameter></paramdef> <paramdef>size_t <parameter>length</parameter></paramdef> </funcprototype> </funcsynopsis> </refsynopsisdiv> <refsect1> <title>Description</title> <para><function>sd_journal_query_unique()</function> queries the journal for all unique values the specified field can take. It takes two arguments: the journal to query and the field name to look for. Well-known field names are listed on <citerefentry><refentrytitle>systemd.journal-fields</refentrytitle><manvolnum>7</manvolnum></citerefentry>. Field names must be specified without a trailing '='. After this function has been executed successfully the field values may be queried using <function>sd_journal_enumerate_unique()</function>. Invoking this call a second time will change the field name being queried and reset the enumeration index to the first field value that matches.</para> <para><function>sd_journal_enumerate_unique()</function> may be used to iterate through all data fields which match the previously selected field name as set with <function>sd_journal_query_unique()</function>. On each invocation the next field data matching the field name is returned. The order of the returned data fields is not defined. It takes three arguments: the journal context object, plus a pair of pointers to pointer/size variables where the data object and its size shall be stored in. The returned data is in a read-only memory map and is only valid until the next invocation of <function>sd_journal_enumerate_unique()</function>. Note that the data returned will be prefixed with the field name and '='. Note that this call is subject to the data field size threshold as controlled by <function>sd_journal_set_data_threshold()</function>.</para> <para><function>sd_journal_restart_unique()</function> resets the data enumeration index to the beginning of the list. The next invocation of <function>sd_journal_enumerate_unique()</function> will return the first field data matching the field name again.</para> <para>Note that the <function>SD_JOURNAL_FOREACH_UNIQUE()</function> macro may be used as a handy wrapper around <function>sd_journal_restart_unique()</function> and <function>sd_journal_enumerate_unique()</function>.</para> <para>Note that these functions currently are not influenced by matches set with <function>sd_journal_add_match()</function> but this might change in a later version of this software.</para> </refsect1> <refsect1> <title>Return Value</title> <para><function>sd_journal_query_unique()</function> returns 0 on success or a negative errno-style error code. <function>sd_journal_enumerate_unique()</function> returns a positive integer if the next field data has been read, 0 when no more fields are known, or a negative errno-style error code. <function>sd_journal_restart_unique()</function> returns nothing.</para> </refsect1> <refsect1> <title>Notes</title> <para>The <function>sd_journal_query_unique()</function>, <function>sd_journal_enumerate_unique()</function> and <function>sd_journal_restart_unique()</function> interfaces are available as a shared library, which can be compiled and linked to with the <constant>libsystemd</constant> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para> </refsect1> <refsect1> <title>Examples</title> <para>Use the <function>SD_JOURNAL_FOREACH_UNIQUE</function> macro to iterate through all values a field of the journal can take. The following example lists all unit names referenced in the journal:</para> <programlisting>#include <stdio.h> #include <string.h> #include <systemd/sd-journal.h> int main(int argc, char *argv[]) { sd_journal *j; const void *d; size_t l; int r; r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY); if (r < 0) { fprintf(stderr, "Failed to open journal: %s\n", strerror(-r)); return 1; } r = sd_journal_query_unique(j, "_SYSTEMD_UNIT"); if (r < 0) { fprintf(stderr, "Failed to query journal: %s\n", strerror(-r)); return 1; } SD_JOURNAL_FOREACH_UNIQUE(j, d, l) printf("%.*s\n", (int) l, (const char*) 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>systemd.journal-fields</refentrytitle><manvolnum>7</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_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry> </para> </refsect1> </refentry>