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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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</style><a href="index.html">Index </a>·
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<a href="../libudev/index.html">gudev </a><span style="float:right">systemd 204</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="idm259782903840"></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="idm259782890000"></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="idm259782878928"></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 shared library, which can
be compiled and linked to with the
<code class="literal">libsystemd-journal</code>
<a href="pkg-config.html"><span class="citerefentry"><span class="refentrytitle">pkg-config</span>(1)</span></a>
file.</p></div><div class="refsect1"><a name="idm259782873808"></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="idm259782869328"></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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