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<html><head><meta http-equiv="Content-Type" content="text/html; charset=UTF-8"><title>sd_journal_query_unique</title><meta name="generator" content="DocBook XSL Stylesheets V1.78.1"></head><body bgcolor="white" text="black" link="#0000FF" vlink="#840084" alink="#0000FF"><style>
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<span style="float:right">systemd 221</span><hr><div class="refentry"><a name="sd_journal_query_unique"></a><div class="titlepage"></div><div class="refnamediv"><h2>Name</h2><p>sd_journal_query_unique, sd_journal_enumerate_unique, sd_journal_restart_unique, SD_JOURNAL_FOREACH_UNIQUE — Read unique data fields from the journal</p></div><div class="refsynopsisdiv"><h2>Synopsis</h2><div class="funcsynopsis"><pre class="funcsynopsisinfo">#include <systemd/sd-journal.h></pre><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">sd_journal_query_unique</b>(</code></td><td>sd_journal *<var class="pdparam">j</var>, </td></tr><tr><td> </td><td>const char *<var class="pdparam">field</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">int <b class="fsfunc">sd_journal_enumerate_unique</b>(</code></td><td>sd_journal *<var class="pdparam">j</var>, </td></tr><tr><td> </td><td>const void **<var class="pdparam">data</var>, </td></tr><tr><td> </td><td>size_t *<var class="pdparam">length</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef">void <b class="fsfunc">sd_journal_restart_unique</b>(</code></td><td>sd_journal *<var class="pdparam">j</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div><table border="0" class="funcprototype-table" summary="Function synopsis" style="cellspacing: 0; cellpadding: 0;"><tr><td><code class="funcdef"><b class="fsfunc">SD_JOURNAL_FOREACH_UNIQUE</b>(</code></td><td>sd_journal *<var class="pdparam">j</var>, </td></tr><tr><td> </td><td>const void *<var class="pdparam">data</var>, </td></tr><tr><td> </td><td>size_t <var class="pdparam">length</var><code>)</code>;</td></tr></table><div class="funcprototype-spacer"> </div></div></div><div class="refsect1"><a name="idm47078173133136"></a><h2 id="Description">Description<a class="headerlink" title="Permalink to this headline" href="#Description">¶</a></h2><p><code class="function">sd_journal_query_unique()</code> 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
<a href="systemd.journal-fields.html"><span class="citerefentry"><span class="refentrytitle">systemd.journal-fields</span>(7)</span></a>.
Field names must be specified without a trailing '='. After this
function has been executed successfully the field values may be
queried using <code class="function">sd_journal_enumerate_unique()</code>.
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.</p><p><code class="function">sd_journal_enumerate_unique()</code> may be
used to iterate through all data fields which match the previously
selected field name as set with
<code class="function">sd_journal_query_unique()</code>. 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
<code class="function">sd_journal_enumerate_unique()</code>. 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
<code class="function">sd_journal_set_data_threshold()</code>.</p><p><code class="function">sd_journal_restart_unique()</code> resets the
data enumeration index to the beginning of the list. The next
invocation of <code class="function">sd_journal_enumerate_unique()</code>
will return the first field data matching the field name
again.</p><p>Note that the
<code class="function">SD_JOURNAL_FOREACH_UNIQUE()</code> macro may be used
as a handy wrapper around
<code class="function">sd_journal_restart_unique()</code> and
<code class="function">sd_journal_enumerate_unique()</code>.</p><p>Note that these functions currently are not influenced by
matches set with <code class="function">sd_journal_add_match()</code> but
this might change in a later version of this software.</p></div><div class="refsect1"><a name="idm47078173121136"></a><h2 id="Return Value">Return Value<a class="headerlink" title="Permalink to this headline" href="#Return%20Value">¶</a></h2><p><code class="function">sd_journal_query_unique()</code> returns 0 on
success or a negative errno-style error code.
<code class="function">sd_journal_enumerate_unique()</code> 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.
<code class="function">sd_journal_restart_unique()</code> returns
nothing.</p></div><div class="refsect1"><a name="idm47078173118080"></a><h2 id="Notes">Notes<a class="headerlink" title="Permalink to this headline" href="#Notes">¶</a></h2><p>The <code class="function">sd_journal_query_unique()</code>,
<code class="function">sd_journal_enumerate_unique()</code> and
<code class="function">sd_journal_restart_unique()</code> interfaces are
available as a shared library, which can be compiled and linked to
with the
<code class="constant">libsystemd</code> <a href="http://linux.die.net/man/1/pkg-config"><span class="citerefentry"><span class="refentrytitle">pkg-config</span>(1)</span></a>
file.</p></div><div class="refsect1"><a name="idm47078173113536"></a><h2 id="Examples">Examples<a class="headerlink" title="Permalink to this headline" href="#Examples">¶</a></h2><p>Use the <code class="function">SD_JOURNAL_FOREACH_UNIQUE</code> macro
to iterate through all values a field of the journal can take. The
following example lists all unit names referenced in the
journal:</p><pre class="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;
}</pre></div><div class="refsect1"><a name="idm47078173109408"></a><h2 id="See Also">See Also<a class="headerlink" title="Permalink to this headline" href="#See%20Also">¶</a></h2><p>
<a href="systemd.html"><span class="citerefentry"><span class="refentrytitle">systemd</span>(1)</span></a>,
<a href="systemd.journal-fields.html"><span class="citerefentry"><span class="refentrytitle">systemd.journal-fields</span>(7)</span></a>,
<a href="sd-journal.html"><span class="citerefentry"><span class="refentrytitle">sd-journal</span>(3)</span></a>,
<a href="sd_journal_open.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_open</span>(3)</span></a>,
<a href="sd_journal_get_data.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_get_data</span>(3)</span></a>,
<a href="sd_journal_add_match.html"><span class="citerefentry"><span class="refentrytitle">sd_journal_add_match</span>(3)</span></a>
</p></div></div></body></html>
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