man: add link to Open Group Base Specifications

[thirdparty/systemd.git] / man / sd_journal_get_realtime_usec.xml

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<!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN"
        "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">

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<refentry id="sd_journal_get_realtime_usec">

        <refentryinfo>
                <title>sd_journal_get_realtime_usec</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_get_realtime_usec</refentrytitle>
                <manvolnum>3</manvolnum>
        </refmeta>

        <refnamediv>
                <refname>sd_journal_get_realtime_usec</refname>
                <refname>sd_journal_get_monotonic_usec</refname>
                <refpurpose>Read timestamps from the current journal entry</refpurpose>
        </refnamediv>

        <refsynopsisdiv>
                <funcsynopsis>
                        <funcsynopsisinfo>#include &lt;systemd/sd-journal.h&gt;</funcsynopsisinfo>

                        <funcprototype>
                                <funcdef>int <function>sd_journal_get_realtime_usec</function></funcdef>
                                <paramdef>sd_journal *<parameter>j</parameter></paramdef>
                                <paramdef>uint64_t *<parameter>usec</parameter></paramdef>
                        </funcprototype>

                        <funcprototype>
                                <funcdef>int <function>sd_journal_get_monotonic_usec</function></funcdef>
                                <paramdef>sd_journal *<parameter>j</parameter></paramdef>
                                <paramdef>uint64_t *<parameter>usec</parameter></paramdef>
                                <paramdef>sd_id128_t *<parameter>boot_id</parameter></paramdef>
                        </funcprototype>

                </funcsynopsis>
        </refsynopsisdiv>

        <refsect1>
                <title>Description</title>

                <para><function>sd_journal_get_realtime_usec()</function>
                gets the realtime (wallclock) timestamp of the
                current journal entry. It takes two arguments: the
                journal context object and a pointer to a 64-bit
                unsigned integer to store the timestamp in. The
                timestamp is in microseconds since the epoch,
                i.e. <constant>CLOCK_REALTIME</constant>.</para>

                <para><function>sd_journal_get_monotonic_usec()</function>
                gets the monotonic timestamp of the current journal
                entry. It takes three arguments: the journal context
                object, a pointer to a 64-bit unsigned integer to
                store the timestamp in, as well as a 128-bit ID buffer
                to store the boot ID of the monotonic timestamp.
                The timestamp is in microseconds since boot-up of
                the specific boot,
                i.e. <constant>CLOCK_MONOTONIC</constant>. Since the
                monotonic clock begins new with every reboot, it only
                defines a well-defined point in time when used
                together with an identifier identifying the boot. See
                <citerefentry><refentrytitle>sd_id128_get_boot</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                for more information. If the boot ID parameter is
                passed <constant>NULL</constant>, the function will
                fail if the monotonic timestamp of the current entry
                is not of the current system boot.</para>

                <para>Note that these functions will not work before
                <citerefentry><refentrytitle>sd_journal_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                (or related call) has been called at least
                once, in order to position the read pointer at a valid entry.</para>
        </refsect1>

        <refsect1>
                <title>Return Value</title>

                <para><function>sd_journal_get_realtime_usec()</function>
                and
                <function>sd_journal_get_monotonic_usec()</function>
                returns 0 on success or a negative errno-style error
                code. If the boot ID parameter was passed <constant>NULL</constant> and the
                monotonic timestamp of the current journal entry is
                not of the current system boot, -ESTALE is returned by <function>sd_journal_get_monotonic_usec()</function>.</para>
        </refsect1>

        <refsect1>
                <title>Notes</title>

                <para>The
                <function>sd_journal_get_realtime_usec()</function>
                and
                <function>sd_journal_get_monotonic_usec()</function>
                interfaces are available as a shared library, which can
                be compiled and linked to with the
                <constant>libsystemd</constant> <citerefentry><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry>
                file.</para>
        </refsect1>

        <refsect1>
                <title>See Also</title>

                <para>
                        <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</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_next</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>sd_journal_get_data</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>sd_id128_get_boot</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>clock_gettime</refentrytitle><manvolnum>2</manvolnum></citerefentry>,
                        <citerefentry><refentrytitle>sd_journal_get_cutoff_realtime_usec</refentrytitle><manvolnum>3</manvolnum></citerefentry>
                </para>
        </refsect1>

</refentry>