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Diffstat (limited to 'man/machine-id.xml')
| -rw-r--r-- | man/machine-id.xml | 230 |
1 files changed, 111 insertions, 119 deletions
diff --git a/man/machine-id.xml b/man/machine-id.xml index 725370d32d..27a8461756 100644 --- a/man/machine-id.xml +++ b/man/machine-id.xml @@ -1,7 +1,7 @@ <?xml version='1.0'?> <!--*-nxml-*--> <?xml-stylesheet type="text/xsl" href="http://docbook.sourceforge.net/release/xsl/current/xhtml/docbook.xsl"?> <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" - "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> + "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> <!-- This file is part of systemd. @@ -23,127 +23,119 @@ --> <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> |