x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
SD_ID128_GET_MACHINE(3) sd_id128_get_machine SD_ID128_GET_MACHINE(3)
NAME
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
#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
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_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:
o The $INVOCATION_ID environment variable that the service manager
sets when activating a service.
o 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).
RETURN VALUE
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.
NOTES
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.
EXAMPLES
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;
}
SEE ALSO
systemd(1), systemd-id128(1), sd-id128(3), machine-id(5),
systemd.exec(5), sd_id128_randomize(3), random(4)
systemd 254 SD_ID128_GET_MACHINE(3)
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