|
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
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.
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 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.
Errors
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.
-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.
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:
/* 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;
}
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 2022-12-17. (At that
time, the date of the most recent commit that was found in the
repository was 2022-12-16.) 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 252 SD_ID128_GET_MACHINE(3)
Pages that refer to this page: systemd-id128(1), 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), networkd.conf(5), systemd.network(5), systemd.directives(7), systemd.index(7), pam_systemd(8)
|
HTML rendering created 2022-12-18 by Michael Kerrisk, author of The Linux Programming Interface, maintainer of the Linux man-pages project. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
|