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- "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
+ "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd">
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<refentry id="machine-id">
- <refentryinfo>
- <title>machine-id</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>machine-id</refentrytitle>
- <manvolnum>5</manvolnum>
- </refmeta>
-
- <refnamediv>
- <refname>machine-id</refname>
- <refpurpose>Local machine ID configuration file</refpurpose>
- </refnamediv>
-
- <refsynopsisdiv>
- <para><filename>/etc/machine-id</filename></para>
- </refsynopsisdiv>
-
- <refsect1>
- <title>Description</title>
-
- <para>The <filename>/etc/machine-id</filename> file
- contains the unique machine ID of the local system
- that is set during installation. The machine ID is a
- single newline-terminated, hexadecimal, 32-character,
- lowercase machine ID string. When decoded from
- hexadecimal, this corresponds with a 16-byte/128-bit
- string.</para>
-
- <para>The machine ID is usually generated from a
- random source during system installation and stays
- constant for all subsequent boots. Optionally, for
- stateless systems, it is generated during runtime at
- boot if it is found to be empty.</para>
-
- <para>The machine ID does not change based on user
- configuration or when hardware is replaced.</para>
-
- <para>This machine ID adheres to the same format and
- logic as the D-Bus machine ID.</para>
-
- <para>Programs may use this ID to identify the host
- with a globally unique ID in the network, which does
- not change even if the local network configuration
- changes. Due to this and its greater length, it is
- a more useful replacement for the
- <citerefentry><refentrytitle>gethostid</refentrytitle><manvolnum>3</manvolnum></citerefentry>
- call that POSIX specifies.</para>
-
- <para>The
- <citerefentry><refentrytitle>systemd-machine-id-setup</refentrytitle><manvolnum>1</manvolnum></citerefentry>
- tool may be used by installer tools to initialize the
- machine ID at install time. Use
- <citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
- to initialize it on mounted (but not booted) system
- images.</para>
- </refsect1>
-
- <refsect1>
- <title>Relation to OSF UUIDs</title>
-
- <para>Note that the machine ID historically is not an
- OSF UUID as defined by <ulink
- url="https://tools.ietf.org/html/rfc4122">RFC
- 4122</ulink>, nor a Microsoft GUID; however, starting with
- systemd v30, newly generated machine IDs do
- qualify as v4 UUIDs.</para>
-
- <para>In order to maintain compatibility with existing
- installations, an application requiring a UUID should
- decode the machine ID, and then apply the following
- operations to turn it into a valid OSF v4 UUID. With
- <literal>id</literal> being an unsigned character
- array:</para>
-
- <programlisting>/* Set UUID version to 4 --- truly random generation */
+ <refentryinfo>
+ <title>machine-id</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>machine-id</refentrytitle>
+ <manvolnum>5</manvolnum>
+ </refmeta>
+
+ <refnamediv>
+ <refname>machine-id</refname>
+ <refpurpose>Local machine ID configuration file</refpurpose>
+ </refnamediv>
+
+ <refsynopsisdiv>
+ <para><filename>/etc/machine-id</filename></para>
+ </refsynopsisdiv>
+
+ <refsect1>
+ <title>Description</title>
+
+ <para>The <filename>/etc/machine-id</filename> file contains the
+ unique machine ID of the local system that is set during
+ installation. The machine ID is a single newline-terminated,
+ hexadecimal, 32-character, lowercase machine ID string. When
+ decoded from hexadecimal, this corresponds with a 16-byte/128-bit
+ string.</para>
+
+ <para>The machine ID is usually generated from a random source
+ during system installation and stays constant for all subsequent
+ boots. Optionally, for stateless systems, it is generated during
+ runtime at boot if it is found to be empty.</para>
+
+ <para>The machine ID does not change based on user configuration
+ or when hardware is replaced.</para>
+
+ <para>This machine ID adheres to the same format and logic as the
+ D-Bus machine ID.</para>
+
+ <para>Programs may use this ID to identify the host with a
+ globally unique ID in the network, which does not change even if
+ the local network configuration changes. Due to this and its
+ greater length, it is a more useful replacement for the
+ <citerefentry><refentrytitle>gethostid</refentrytitle><manvolnum>3</manvolnum></citerefentry>
+ call that POSIX specifies.</para>
+
+ <para>The
+ <citerefentry><refentrytitle>systemd-machine-id-setup</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ tool may be used by installer tools to initialize the machine ID
+ at install time. Use
+ <citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ to initialize it on mounted (but not booted) system images.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>Relation to OSF UUIDs</title>
+
+ <para>Note that the machine ID historically is not an OSF UUID as
+ defined by <ulink url="https://tools.ietf.org/html/rfc4122">RFC
+ 4122</ulink>, nor a Microsoft GUID; however, starting with systemd
+ v30, newly generated machine IDs do qualify as v4 UUIDs.</para>
+
+ <para>In order to maintain compatibility with existing
+ installations, an application requiring a UUID should decode the
+ machine ID, and then apply the following operations to turn it
+ into a valid OSF v4 UUID. With <literal>id</literal> being an
+ unsigned character array:</para>
+
+ <programlisting>/* Set UUID version to 4 --- truly random generation */
id[6] = (id[6] & 0x0F) | 0x40;
/* Set the UUID variant to DCE */
id[8] = (id[8] & 0x3F) | 0x80;</programlisting>
- <para>(This code is inspired by
- <literal>generate_random_uuid()</literal> of
- <filename>drivers/char/random.c</filename> from the
- Linux kernel sources.)</para>
-
- </refsect1>
-
- <refsect1>
- <title>History</title>
-
- <para>The simple configuration file format of
- <filename>/etc/machine-id</filename> originates in the
- <filename>/var/lib/dbus/machine-id</filename> file
- introduced by D-Bus. In fact, this latter file might be a
- symlink to
- <varname>/etc/machine-id</varname>.</para>
- </refsect1>
-
- <refsect1>
- <title>See Also</title>
- <para>
- <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>systemd-machine-id-setup</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>gethostid</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>hostname</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>machine-info</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>sd_id128_get_machine</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
- <citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
- </para>
- </refsect1>
+ <para>(This code is inspired by
+ <literal>generate_random_uuid()</literal> of
+ <filename>drivers/char/random.c</filename> from the Linux kernel
+ sources.)</para>
+
+ </refsect1>
+
+ <refsect1>
+ <title>History</title>
+
+ <para>The simple configuration file format of
+ <filename>/etc/machine-id</filename> originates in the
+ <filename>/var/lib/dbus/machine-id</filename> file introduced by
+ D-Bus. In fact, this latter file might be a symlink to
+ <varname>/etc/machine-id</varname>.</para>
+ </refsect1>
+
+ <refsect1>
+ <title>See Also</title>
+ <para>
+ <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd-machine-id-setup</refentrytitle><manvolnum>1</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>gethostid</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>hostname</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>machine-info</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>os-release</refentrytitle><manvolnum>5</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>sd_id128_get_machine</refentrytitle><manvolnum>3</manvolnum></citerefentry>,
+ <citerefentry><refentrytitle>systemd-firstboot</refentrytitle><manvolnum>1</manvolnum></citerefentry>
+ </para>
+ </refsect1>
</refentry>
~ianmdlvl / elogind.git / blobdiff