217 lines
9.8 KiB
XML
217 lines
9.8 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_query_unique">
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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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<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_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_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_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>
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queries the journal for all unique values the
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specified field can take. It takes two arguments: the
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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>. Field
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names must be specified without a trailing '='. After
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this function has been executed successfully the field
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values may be queried using
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<function>sd_journal_enumerate_unique()</function>. Invoking
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this call a second time will change the field name
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being queried and reset the enumeration index to the
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first field value that matches.</para>
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<para><function>sd_journal_enumerate_unique()</function>
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may be used to iterate through all data fields which
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match the previously selected field name as set with
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<function>sd_journal_query_unique()</function>. On
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each invocation the next field data matching the field
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name is returned. The order of the returned data
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fields is not defined. It takes three arguments: the
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journal context object, 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 returned data is in a
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read-only memory map and is only valid until the next
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invocation of
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<function>sd_journal_enumerate_unique()</function>. Note
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that the data returned will be prefixed with the field
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name and '='. Note that this call is subject to the
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data field size threshold as controlled by
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<function>sd_journal_set_data_threshold()</function>.</para>
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<para><function>sd_journal_restart_unique()</function>
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resets the data enumeration index to the beginning of
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the list. The next invocation of
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<function>sd_journal_enumerate_unique()</function>
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will return the first field data matching the field
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name again.</para>
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<para>Note that the
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<function>SD_JOURNAL_FOREACH_UNIQUE()</function> macro
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may be used as a handy wrapper around
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<function>sd_journal_restart_unique()</function> and
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<function>sd_journal_enumerate_unique()</function>.</para>
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<para>Note that these functions currently are not
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influenced by matches set with
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<function>sd_journal_add_match()</function> but this
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might change in a later version of this
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software.</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>
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returns 0 on success or a negative errno-style error
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code. <function>sd_journal_enumerate_unique()</function>
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returns a positive integer if the next field data has
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been read, 0 when no more fields are known, or a
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negative errno-style error
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code. <function>sd_journal_restart_unique()</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_query_unique()</function>,
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<function>sd_journal_enumerate_unique()</function> and
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<function>sd_journal_restart_unique()</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>Use the
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<function>SD_JOURNAL_FOREACH_UNIQUE</function> macro
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to iterate through all values a field of the journal
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can take. The following example lists all unit names
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referenced in the journal:</para>
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<programlisting>#include <stdio.h>
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#include <string.h>
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#include <systemd/sd-journal.h>
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int main(int argc, char *argv[]) {
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sd_journal *j;
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const void *d;
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size_t l;
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int r;
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r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY);
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if (r < 0) {
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fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
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return 1;
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}
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r = sd_journal_query_unique(j, "_SYSTEMD_UNIT");
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if (r < 0) {
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fprintf(stderr, "Failed to query journal: %s\n", strerror(-r));
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return 1;
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}
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SD_JOURNAL_FOREACH_UNIQUE(j, d, l)
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printf("%.*s\n", (int) l, (const char*) d);
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sd_journal_close(j);
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return 0;
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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_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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