MACHINE-ID(5) machine-id MACHINE-ID(5) (NAME) machine-id - (SYNOPSIS) /etc/machine-id (DESCRIPTION) /etc/machine-id (machine ID) . . / . . . (stateless) . systemd.machine_id= --machine-id= systemd . /etc/machine-id . . gethostid(3) POSIX . D-Bus . . <<>> . . . . sd_id128_get_machine_app_specific(3) . (INITIALIZATION) . . /etc/machine-id . /etc/machine-id . systemd-machine-id-setup(1) /etc/machine-id . ( ) /etc/machine-id ( << >> ). . bind-mount /etc (mount) . : Safely Building Images[1]. systemd-firstboot(1) /etc/machine-id ( ) . systemd(1) . systemd.machine_id= --machine-id= ( ) . /etc/machine-id . systemd D-Bus /var/lib/dbus/machine-id container_uuid KVM DMI product_uuid devicetree vm,uuid ( KVM) Xen hypervisor uuid UUID . systemd.machine_id=firmware . systemd(1) /etc/machine-id . /etc/machine-id bind-mount . ( ) /etc/machine-id . systemd-machine-id-commit.service(8) /etc/machine-id /etc/ . (FIRST BOOT SEMANTICS) /etc/machine-id . : 1. systemd.condition_first_boot= : kernel- command-line(7). 2. /etc/machine-id . systemd "uninitialized\n" mount . ( first-boot-complete.target) . 3. /etc/machine-id "uninitialized" . . 4. /etc/machine-id not . systemd bind-mount ( /etc/ ). 5. /etc/machine-id . ConditionFirstBoot=yes systemd (presetting units) . OSF UUID (RELATION TO OSF UUIDS) OSF UUID RFC 4122[2] Microsoft GUID v30 systemd RFC 4122 Variant 1 Version 4 UUID . UUID RFC 4122 ( ) RFC 4122 Variant 1 Version 4 UUID . "id" (unsigned char) : /* 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; ( "generate_random_uuid()" drivers/char/random.c .) (HISTORY) /etc/machine-id /var/lib/dbus/machine-id D-Bus . (symlink) /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. Safely Building Images https://systemd.io/BUILDING_IMAGES 2. RFC 4122 https://tools.ietf.org/html/rfc4122 systemd 257.13 MACHINE-ID(5)