1MACHINE-ID(5) machine-id MACHINE-ID(5)
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6 machine-id - Local machine ID configuration file
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9 /etc/machine-id
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12 The /etc/machine-id file contains the unique machine ID of the local
13 system that is set during installation. The machine ID is a single
14 newline-terminated, hexadecimal, 32-character, lowercase machine ID
15 string. When decoded from hexadecimal, this corresponds with a
16 16-byte/128-bit string.
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18 The machine ID is usually generated from a random source during system
19 installation and stays constant for all subsequent boots. Optionally,
20 for stateless systems, it is generated during runtime at boot if it is
21 found to be empty.
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23 The machine ID does not change based on user configuration or when
24 hardware is replaced.
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26 This machine ID adheres to the same format and logic as the D-Bus
27 machine ID.
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29 Programs may use this ID to identify the host with a globally unique ID
30 in the network, which does not change even if the local network
31 configuration changes. Due to this and its greater length, it is a more
32 useful replacement for the gethostid(3) call that POSIX specifies.
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34 The systemd-machine-id-setup(1) tool may be used by installer tools to
35 initialize the machine ID at install time. Use systemd-firstboot(1) to
36 initialize it on mounted (but not booted) system images.
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39 Note that the machine ID historically is not an OSF UUID as defined by
40 RFC 4122[1], nor a Microsoft GUID; however, starting with systemd v30,
41 newly generated machine IDs do qualify as v4 UUIDs.
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43 In order to maintain compatibility with existing installations, an
44 application requiring a UUID should decode the machine ID, and then
45 apply the following operations to turn it into a valid OSF v4 UUID.
46 With "id" being an unsigned character array:
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48 /* Set UUID version to 4 --- truly random generation */
49 id[6] = (id[6] & 0x0F) | 0x40;
50 /* Set the UUID variant to DCE */
51 id[8] = (id[8] & 0x3F) | 0x80;
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53 (This code is inspired by "generate_random_uuid()" of
54 drivers/char/random.c from the Linux kernel sources.)
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57 The simple configuration file format of /etc/machine-id originates in
58 the /var/lib/dbus/machine-id file introduced by D-Bus. In fact, this
59 latter file might be a symlink to /etc/machine-id.
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62 systemd(1), systemd-machine-id-setup(1), gethostid(3), hostname(5),
63 machine-info(5), os-release(5), sd-id128(3), sd_id128_get_machine(3),
64 systemd-firstboot(1)
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67 1. RFC 4122
68 https://tools.ietf.org/html/rfc4122
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72systemd 219 MACHINE-ID(5)