<?xml version='1.0'?> <!--*-nxml-*--> <!DOCTYPE refentry PUBLIC "-//OASIS//DTD DocBook XML V4.2//EN" "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> <!-- SPDX-License-Identifier: LGPL-2.1+ This file is part of systemd. Copyright 2012 Lennart Poettering systemd is free software; you can redistribute it and/or modify it under the terms of the GNU Lesser General Public License as published by the Free Software Foundation; either version 2.1 of the License, or (at your option) any later version. systemd is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE. See the GNU Lesser General Public License for more details. You should have received a copy of the GNU Lesser General Public License along with systemd; If not, see <http://www.gnu.org/licenses/>. --> <refentry id="sd_id128_get_machine"> <refentryinfo> <title>sd_id128_get_machine</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_id128_get_machine</refentrytitle> <manvolnum>3</manvolnum> </refmeta> <refnamediv> <refname>sd_id128_get_machine</refname> <refname>sd_id128_get_machine_app_specific</refname> <refname>sd_id128_get_boot</refname> <refname>sd_id128_get_invocation</refname> <refpurpose>Retrieve 128-bit IDs</refpurpose> </refnamediv> <refsynopsisdiv> <funcsynopsis> <funcsynopsisinfo>#include <systemd/sd-id128.h></funcsynopsisinfo> <funcprototype> <funcdef>int <function>sd_id128_get_machine</function></funcdef> <paramdef>sd_id128_t *<parameter>ret</parameter></paramdef> </funcprototype> <funcprototype> <funcdef>int <function>sd_id128_get_machine_app_specific</function></funcdef> <paramdef>sd_id128_t <parameter>app_id</parameter></paramdef> <paramdef>sd_id128_t *<parameter>ret</parameter></paramdef> </funcprototype> <funcprototype> <funcdef>int <function>sd_id128_get_boot</function></funcdef> <paramdef>sd_id128_t *<parameter>ret</parameter></paramdef> </funcprototype> <funcprototype> <funcdef>int <function>sd_id128_get_invocation</function></funcdef> <paramdef>sd_id128_t *<parameter>ret</parameter></paramdef> </funcprototype> </funcsynopsis> </refsynopsisdiv> <refsect1> <title>Description</title> <para><function>sd_id128_get_machine()</function> returns the machine ID of the executing host. This reads and parses the <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry> file. This function caches the machine ID internally to make retrieving the machine ID a cheap operation. This ID may be used wherever a unique identifier for the local system is needed. However, it is recommended to use this ID as-is only in trusted environments. In untrusted environments it is recommended to derive an application specific ID from this machine ID, in an irreversable (cryptographically secure) way. To make this easy <function>sd_id128_get_machine_app_specific()</function> is provided, see below.</para> <para><function>sd_id128_get_machine_app_specific()</function> is similar to <function>sd_id128_get_machine()</function>, but retrieves a machine ID that is specific to the application that is identified by the indicated application ID. It is recommended to use this function instead of <function>sd_id128_get_machine()</function> when passing an ID to untrusted environments, in order to make sure that the original machine ID may not be determined externally. The application-specific ID should be generated via a tool like <command>journalctl --new-id128</command>, and may be compiled into the application. This function will return the same application-specific ID for each combination of machine ID and application ID. Internally, this function calculates HMAC-SHA256 of the application ID, keyed by the machine ID.</para> <para><function>sd_id128_get_boot()</function> returns the boot ID of the executing kernel. This reads and parses the <filename>/proc/sys/kernel/random/boot_id</filename> file exposed by the kernel. It is randomly generated early at boot and is unique for every running kernel instance. See <citerefentry project='man-pages'><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry> for more information. This function also internally caches the returned ID to make this call a cheap operation.</para> <para><function>sd_id128_get_invocation()</function> returns the invocation ID of the currently executed service. In its current implementation, this reads and parses the <varname>$INVOCATION_ID</varname> environment variable that the service manager sets when activating a service, see <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry> for details. The ID is cached internally. In future a different mechanism to determine the invocation ID may be added.</para> <para>Note that <function>sd_id128_get_machine_app_specific()</function>, <function>sd_id128_get_boot()</function> and <function>sd_id128_get_invocation()</function> always return UUID v4 compatible IDs. <function>sd_id128_get_machine()</function> will also return a UUID v4-compatible ID on new installations but might not on older. It is possible to convert the machine ID into a UUID v4-compatible one. For more information, see <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>.</para> <para>For more information about the <literal>sd_id128_t</literal> type see <citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>.</para> </refsect1> <refsect1> <title>Return Value</title> <para>The two calls return 0 on success (in which case <parameter>ret</parameter> is filled in), or a negative errno-style error code.</para> </refsect1> <refsect1> <title>Notes</title> <para>The <function>sd_id128_get_machine()</function>, <function>sd_id128_get_machine_app_specific()</function> <function>sd_id128_get_boot()</function> and <function>sd_id128_get_invocation()</function> interfaces are available as a shared library, which can be compiled and linked to with the <literal>libsystemd</literal> <citerefentry project='die-net'><refentrytitle>pkg-config</refentrytitle><manvolnum>1</manvolnum></citerefentry> file.</para> </refsect1> <refsect1> <title>Examples</title> <example> <title>Application-specific machine ID</title> <para>Here's a simple example for an application specific machine ID:</para> <programlisting>#include <systemd/sd-id128.h> #include <stdio.h> #define OUR_APPLICATION_ID SD_ID128_MAKE(c2,73,27,73,23,db,45,4e,a6,3b,b9,6e,79,b5,3e,97) int main(int argc, char *argv[]) { sd_id128_t id; sd_id128_get_machine_app_specific(OUR_APPLICATION_ID, &id); printf("Our application ID: " SD_ID128_FORMAT_STR "\n", SD_ID128_FORMAT_VAL(id)); return 0; }</programlisting> </example> </refsect1> <refsect1> <title>See Also</title> <para> <citerefentry><refentrytitle>systemd</refentrytitle><manvolnum>1</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd-id128</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry><refentrytitle>machine-id</refentrytitle><manvolnum>5</manvolnum></citerefentry>, <citerefentry><refentrytitle>systemd.exec</refentrytitle><manvolnum>5</manvolnum></citerefentry>, <citerefentry><refentrytitle>sd_id128_randomize</refentrytitle><manvolnum>3</manvolnum></citerefentry>, <citerefentry project='man-pages'><refentrytitle>random</refentrytitle><manvolnum>4</manvolnum></citerefentry> </para> </refsect1> </refentry>