X-Git-Url: https://www.chiark.greenend.org.uk/ucgi/~ianmdlvl/git?p=elogind.git;a=blobdiff_plain;f=man%2Fmachine-id.xml;h=83e0b26ced217ea6ce5597e0ada231184b72fb21;hp=7d424b705b12d86dc5f55f2b2b25d117c1e8630e;hb=edbda61f25324e8e86c2bd76f3fcf7247e0c34b5;hpb=34511ca7b166b0e89d08ff9870b0cf2624a7815f diff --git a/man/machine-id.xml b/man/machine-id.xml index 7d424b705..83e0b26ce 100644 --- a/man/machine-id.xml +++ b/man/machine-id.xml @@ -1,7 +1,6 @@ - + "http://www.oasis-open.org/docbook/xml/4.2/docbookx.dtd"> - - /etc/machine-id - systemd - - - - Developer - Lennart - Poettering - lennart@poettering.net - - - - - - machine-id - 5 - - - - machine-id - Local machine ID configuration file - - - - /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, lowercase 32 - character 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 - 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, that 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 - gethostid3 - call POSIX specifies. - - The - systemd-machine-id-setup1 - tool may be used by installer tools to initialize the - machine ID at install time. - - - - Relation to OSF UUIDs - - Note that the machine ID historically is not an - OSF UUID as defined by RFC - 4122, nor a Microsoft GUID. Starting with - systemd v30 newly generated machine IDs however 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 */ + + machine-id + systemd + + + + Developer + Lennart + Poettering + lennart@poettering.net + + + + + + machine-id + 5 + + + + machine-id + Local machine ID configuration file + + + + /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 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 + gethostid3 + call that POSIX specifies. + + The + systemd-machine-id-setup1 + tool may be used by installer tools to initialize the machine ID + at install time. Use + systemd-firstboot1 + to initialize it on mounted (but not booted) system images. + + + + Relation to OSF UUIDs + + Note that the machine ID historically is not an OSF UUID as + defined by RFC + 4122, 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 - 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 - - systemd1, - systemd-machine-id-setup1, - gethostid3, - hostname5, - machine-info5, - os-release5, - sd-id1283, - sd_id128_get_machine3 - - + (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 + + systemd1, + systemd-machine-id-setup1, + gethostid3, + hostname5, + machine-info5, + os-release5, + sd-id1283, + sd_id128_get_machine3, + systemd-firstboot1 + +