sd_id128_get_machine, sd_id128_get_app_specific, 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_app_specific( | sd_id128_t base, |
sd_id128_t app_id, | |
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) ; |
int sd_id128_get_invocation_app_specific( | sd_id128_t app_id, |
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_app_specific()
returns a machine ID that is a combination of the
base
and app_id
parameters. Internally, this function
calculates HMAC-SHA256 of the app_id
parameter keyed by the
base
parameter, and truncates this result to fit in
sd_id128_t and turns it into a valid Variant 1 Version 4 UUID, in accordance
with RFC 4122. Neither of the two input
parameters can be calculated from the output parameter ret
.
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 calls sd_id128_get_app_specific()
with the result from
sd_id128_get_machine()
and the app_id
parameter.
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_boot_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 tries to read and parse the following:
The $INVOCATION_ID
environment variable that the service manager sets when
activating a service.
An entry in the kernel keyring that the system 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.
sd_id128_get_invocation_app_specific()
derives an application-specific ID from
the invocation ID.
Note that sd_id128_get_machine_app_specific()
,
sd_id128_get_boot()
, sd_id128_get_boot_app_specific()
,
sd_id128_get_invocation()
and
sd_id128_get_invocation_app_specific
always return UUID Variant 1 Version 4
compatible IDs. sd_id128_get_machine()
will also return a UUID Variant 1 Version 4
compatible ID on new installations but might not on older. It is possible to convert the machine ID
non-reversibly into a UUID Variant 1 Version 4 compatible one. For more information, see
machine-id(5). It is
hence guaranteed that these functions will never return the ID consisting of all zero or all one bits
(SD_ID128_NULL
, SD_ID128_ALLF
) — with the possible exception of
sd_id128_get_machine()
, as mentioned.
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.
Returned errors may indicate the following problems:
-ENOENT
¶Returned by sd_id128_get_machine()
and
sd_id128_get_machine_app_specific()
when /etc/machine-id
is missing.
-ENOMEDIUM
¶Returned by sd_id128_get_machine()
and
sd_id128_get_machine_app_specific()
when /etc/machine-id
is empty or all zeros. Also returned by sd_id128_get_invocation()
when the
invocation ID is all zeros.
-ENOPKG
¶Returned by sd_id128_get_machine()
and
sd_id128_get_machine_app_specific()
when the content of
/etc/machine-id
is "uninitialized
".
-ENOSYS
¶Returned by sd_id128_get_boot()
and
sd_id128_get_boot_app_specific()
when /proc/
is not
mounted.
-ENXIO
¶Returned by sd_id128_get_invocation()
if no invocation ID is
set. Also returned by sd_id128_get_app_specific()
,
sd_id128_get_machine_app_specific()
, and
sd_id128_get_boot_app_specific()
when the app_id
parameter is all zeros.
-EUCLEAN
¶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.
Functions described here are available as a shared
library, which can be compiled against and linked to with the
libsystemd
pkg-config(1)
file.
The code described here uses
getenv(3),
which is declared to be not multi-thread-safe. This means that the code calling the functions described
here must not call
setenv(3)
from a parallel thread. It is recommended to only do calls to setenv()
from an early phase of the program when no other threads have been started.
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:
/* SPDX-License-Identifier: MIT-0 */ #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; }
sd_id128_get_machine()
and
sd_id128_get_boot()
were added in version 187.
sd_id128_get_invocation()
was added in version 232.
sd_id128_get_machine_app_specific()
was added in version 233.
sd_id128_get_boot_app_specific()
was added in version 240.
sd_id128_get_app_specific()
was added in version 255.
sd_id128_get_invocation_app_specific()
was added in version 256.