SD_ID128_GET_MACHINE(3)     sd_id128_get_machine     SD_ID128_GET_MACHINE(3)

NAME         top

       sd_id128_get_machine, sd_id128_get_machine_app_specific,
       sd_id128_get_boot, sd_id128_get_invocation - Retrieve 128-bit IDs

SYNOPSIS         top

       #include <systemd/sd-id128.h>

       int sd_id128_get_machine(sd_id128_t *ret);

       int sd_id128_get_machine_app_specific(sd_id128_t app_id,
                                             sd_id128_t *ret);

       int sd_id128_get_boot(sd_id128_t *ret);

       int sd_id128_get_invocation(sd_id128_t *ret);

DESCRIPTION         top

       sd_id128_get_machine() returns the machine ID of the executing host.
       This reads and parses the machine-id(5) 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 sd_id128_get_machine_app_specific() is provided, see below.

       sd_id128_get_machine_app_specific() is similar to
       sd_id128_get_machine(), 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
       sd_id128_get_machine() 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 journalctl --new-id128, 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.

       sd_id128_get_boot() returns the boot ID of the executing kernel. This
       reads and parses the /proc/sys/kernel/random/boot_id file exposed by
       the kernel. It is randomly generated early at boot and is unique for
       every running kernel instance. See random(4) for more information.
       This function also internally caches the returned ID to make this
       call a cheap operation.

       sd_id128_get_invocation() returns the invocation ID of the currently
       executed service. In its current implementation, this reads and
       parses the $INVOCATION_ID environment variable that the service
       manager sets when activating a service, see systemd.exec(5) for
       details. The ID is cached internally. In future a different mechanism
       to determine the invocation ID may be added.

       Note that sd_id128_get_machine_app_specific(), sd_id128_get_boot()
       and sd_id128_get_invocation() always return UUID v4 compatible IDs.
       sd_id128_get_machine() 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 machine-id(5).

       For more information about the "sd_id128_t" type see sd-id128(3).

RETURN VALUE         top

       The two calls return 0 on success (in which case ret is filled in),
       or a negative errno-style error code.

NOTES         top

       The sd_id128_get_machine(),
       sd_id128_get_machine_app_specific()sd_id128_get_boot() and
       sd_id128_get_invocation() interfaces are available as a shared
       library, which can be compiled and linked to with the
       "libsystemd" pkg-config(1) file.

EXAMPLES         top

       Example 1. Application-specific machine ID

       Here's a simple example for an application specific machine ID:

           #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;

SEE ALSO         top

       systemd(1), sd-id128(3), machine-id(5), systemd.exec(5),
       sd_id128_randomize(3), random(4)

COLOPHON         top

       This page is part of the systemd (systemd system and service manager)
       project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug
       report for this manual page, see
       ⟨⟩.  This
       page was obtained from the project's upstream Git repository
       ⟨⟩ on 2019-05-09.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2019-05-09.)  If you discover any rendering problems in
       this HTML version of the page, or you believe there is a better or
       more up-to-date source for the page, or you have corrections or
       improvements to the information in this COLOPHON (which is not part
       of the original manual page), send a mail to

systemd 234                                          SD_ID128_GET_MACHINE(3)

Pages that refer to this page: sd_bus_message_get_monotonic_usec(3)sd-id128(3)sd_id128_randomize(3)sd_journal_get_cutoff_realtime_usec(3)sd_journal_get_realtime_usec(3)machine-id(5)systemd.directives(7)systemd.index(7)