<para>Entries in the journal resemble an environment
block in their syntax, however with fields that can
include binary data. Primarily, fields are formatted
- ASCII strings, and binary formatting is used only
- where formatting as ASCII makes little sense. New
- fields may be freely defined by applications, but a
- few fields have special meaning. All fields with
- special meaning are optional.</para>
+ UTF-8 text strings, and binary formatting is used only
+ where formatting as UTF-8 text strings makes little
+ sense. New fields may freely be defined by
+ applications, but a few fields have special
+ meaning. All fields with special meanings are
+ optional.</para>
</refsect1>
<refsect1>
</listitem>
</varlistentry>
+ <varlistentry>
+ <term>ERRNO=</term>
+ <listitem>
+ <para>The low-level Unix error
+ number causing this entry, if
+ any. Contains the numeric
+ value of
+ <citerefentry><refentrytitle>errno</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ formatted as decimal
+ string.</para>
+ </listitem>
+ </varlistentry>
+
<varlistentry>
<term>SYSLOG_FACILITY=</term>
<term>SYSLOG_IDENTIFIER=</term>
addresses of journal entries are serialized into
fields prefixed with double underscores. Note that
these aren't proper fields when stored in the journal,
- but addressing meta data of entries.</para>
+ but addressing meta data of entries. They cannot be
+ written as part of structured log entries via calls
+ such as
+ <citerefentry><refentrytitle>sd_journal_send</refentrytitle><manvolnum>3</manvolnum></citerefentry>. They
+ may also not be used as matches for
+ <citerefentry><refentrytitle>sd_journal_add_match</refentrytitle><manvolnum>3</manvolnum></citerefentry></para>
<variablelist>
<varlistentry>
<para>
<citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
<citerefentry><refentrytitle>journalctl</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>
+ <citerefentry><refentrytitle>journald.conf</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd-journal</refentrytitle><manvolnum>3</manvolnum></citerefentry>
</para>
</refsect1>