sd_id128_get_boot_app_specific(3) — Linux manual page


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_boot_app_specific,
       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_boot_app_specific(sd_id128_t app_id,
                                          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 irreversible (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. This way, the ID used by the application
       remains stable on a given machine, but cannot be easily correlated
       with IDs used in other applications on the same machine. The
       application-specific ID should be generated via a tool like
       systemd-id128 new, 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. 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 using
       sd_id128_get_machine_app_specific(), see below.

       sd_id128_get_boot_app_specific() is analogous to
       sd_id128_get_machine_app_specific() but returns an ID that changes
       between boots. Some machines may be used for a long time without
       rebooting, hence the boot ID may remain constant for a long time, and
       has properties similar to the machine ID during that time.

       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(),
       sd_id128_get_boot_app_specific(), 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

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

       Returned errors may indicate the following problems:

           Returned by sd_id128_get_machine(),
           sd_id128_get_machine_app_specific(), and
           sd_id128_get_boot_app_specific() when /etc/machine-id is missing.

           Returned by sd_id128_get_machine(),
           sd_id128_get_machine_app_specific(), and
           sd_id128_get_boot_app_specific() when /etc/machine-id is empty or
           all zeros.

           Returned by sd_id128_get_invocation() if no invocation ID is set.

           Returned by any of the functions described here when the
           configured value has invalid format.

           Requested information could not be retrieved because of
           insufficient permissions.

NOTES         top

       These APIs are implemented 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

       First, generate the application ID:

           $ systemd-id128 -p new
           As string:

           As UUID:

           As man:sd-id128(3) macro:
           #define MESSAGE_XYZ SD_ID128_MAKE(c2,73,27,73,23,db,45,4e,a6,3b,b9,6e,79,b5,3e,97)

       Then use the new identifier in an example application:

           #include <stdio.h>
           #include <systemd/sd-id128.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), systemd-id128(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)
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       report for this manual page, see
       ⟨⟩.  This
       page was obtained from the project's upstream Git repository
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systemd 246                                          SD_ID128_GET_MACHINE(3)

Pages that refer to this page: 30-systemd-environment-d-generator(7)systemd.index(7)