Free Knowledge Resources


Linux Manual Pages


Free Software * Books

Source Code

Free Media

Linux

machine-id(5)


NAME

   machine-id - Local machine ID configuration file

SYNOPSIS

   /etc/machine-id

DESCRIPTION

   The /etc/machine-id 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.

   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 early boot if
   it is found to be empty.

   The machine ID does not change based on user configuration or when
   hardware is replaced.

   This machine ID adheres to the same format and logic as the D-Bus
   machine ID.

   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 gethostid(3) call that POSIX specifies.

   The systemd-machine-id-setup(1) tool may be used by installer tools to
   initialize the machine ID at install time. Use systemd-firstboot(1) to
   initialize it on mounted (but not booted) system images.

   The machine-id may also be set, for example when network booting, by
   setting the systemd.machine_id= kernel command line parameter or
   passing the option --machine-id= to systemd. A machine-id may not be
   set to all zeros.

RELATION TO OSF UUIDS

   Note that the machine ID historically is not an OSF UUID as defined by
   RFC 4122[1], nor a Microsoft GUID; however, starting with systemd v30,
   newly generated machine IDs do qualify as v4 UUIDs.

   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 "id" being an unsigned character array:

       /* 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;

   (This code is inspired by "generate_random_uuid()" of
   drivers/char/random.c from the Linux kernel sources.)

HISTORY

   The simple configuration file format of /etc/machine-id originates in
   the /var/lib/dbus/machine-id file introduced by D-Bus. In fact, this
   latter file might be a symlink to /etc/machine-id.

SEE ALSO

   systemd(1), systemd-machine-id-setup(1), gethostid(3), hostname(5),
   machine-info(5), os-release(5), sd-id128(3), sd_id128_get_machine(3),
   systemd-firstboot(1)

NOTES

    1. RFC 4122
       https://tools.ietf.org/html/rfc4122



Opportunity


Personal Opportunity - Free software gives you access to billions of dollars of software at no cost. Use this software for your business, personal use or to develop a profitable skill. Access to source code provides access to a level of capabilities/information that companies protect though copyrights. Open source is a core component of the Internet and it is available to you. Leverage the billions of dollars in resources and capabilities to build a career, establish a business or change the world. The potential is endless for those who understand the opportunity.

Business Opportunity - Goldman Sachs, IBM and countless large corporations are leveraging open source to reduce costs, develop products and increase their bottom lines. Learn what these companies know about open source and how open source can give you the advantage.



Free Software


Free Software provides computer programs and capabilities at no cost but more importantly, it provides the freedom to run, edit, contribute to, and share the software. The importance of free software is a matter of access, not price. Software at no cost is a benefit but ownership rights to the software and source code is far more significant.

Free Office Software - The Libre Office suite provides top desktop productivity tools for free. This includes, a word processor, spreadsheet, presentation engine, drawing and flowcharting, database and math applications. Libre Office is available for Linux or Windows.



Free Books


The Free Books Library is a collection of thousands of the most popular public domain books in an online readable format. The collection includes great classical literature and more recent works where the U.S. copyright has expired. These books are yours to read and use without restrictions.

Source Code - Want to change a program or know how it works? Open Source provides the source code for its programs so that anyone can use, modify or learn how to write those programs themselves. Visit the GNU source code repositories to download the source.



Education


Study at Harvard, Stanford or MIT - Open edX provides free online courses from Harvard, MIT, Columbia, UC Berkeley and other top Universities. Hundreds of courses for almost all major subjects and course levels. Open edx also offers some paid courses and selected certifications.

Linux Manual Pages - A man or manual page is a form of software documentation found on Linux/Unix operating systems. Topics covered include computer programs (including library and system calls), formal standards and conventions, and even abstract concepts.


birds banner