|
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | EXAMPLES | SEE ALSO | COLOPHON |
SD_ID128_GET_MACHINE(3) sd_id128_get_machine SD_ID128_GET_MACHINE(3)
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
#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);
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).
Those calls return 0 on success (in which case ret is filled in), or
a negative errno-style error code.
Errors
Returned errors may indicate the following problems:
-ENOENT
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.
-ENOMEDIUM
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.
-ENXIO
Returned by sd_id128_get_invocation() if no invocation ID is set.
-EIO
Returned by any of the functions described here when the
configured value has invalid format.
-EPERM
Requested information could not be retrieved because of
insufficient permissions.
These APIs are implemented as a shared library, which can be compiled
and linked to with the libsystemd pkg-config(1) file.
Example 1. Application-specific machine ID
First, generate the application ID:
$ systemd-id128 -p new
As string:
c273277323db454ea63bb96e79b53e97
As UUID:
c2732773-23db-454e-a63b-b96e79b53e97
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;
}
systemd(1), systemd-id128(1), sd-id128(3), machine-id(5),
systemd.exec(5), sd_id128_randomize(3), random(4)
This page is part of the systemd (systemd system and service manager)
project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a bug
report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩. This
page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2020-08-13. (At that
time, the date of the most recent commit that was found in the repos‐
itory was 2020-08-11.) 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 man-pages@man7.org
systemd 246 SD_ID128_GET_MACHINE(3)
Pages that refer to this page: machine-id(5) , networkd.conf(5) , networkd.conf.d(5) , 30-systemd-environment-d-generator(7) , systemd.index(7)