sd_id128_get_boot_app_specific(3)

1SD_ID128_GET_MACHINE(3)      sd_id128_get_machine      SD_ID128_GET_MACHINE(3)
2
3
4

NAME

6       sd_id128_get_machine, sd_id128_get_machine_app_specific,
7       sd_id128_get_boot, sd_id128_get_boot_app_specific,
8       sd_id128_get_invocation - Retrieve 128-bit IDs
9

SYNOPSIS

11       #include <systemd/sd-id128.h>
12
13       int sd_id128_get_machine(sd_id128_t *ret);
14
15       int sd_id128_get_machine_app_specific(sd_id128_t app_id,
16                                             sd_id128_t *ret);
17
18       int sd_id128_get_boot(sd_id128_t *ret);
19
20       int sd_id128_get_boot_app_specific(sd_id128_t app_id, sd_id128_t *ret);
21
22       int sd_id128_get_invocation(sd_id128_t *ret);
23

DESCRIPTION

25       sd_id128_get_machine() returns the machine ID of the executing host.
26       This reads and parses the machine-id(5) file. This function caches the
27       machine ID internally to make retrieving the machine ID a cheap
28       operation. This ID may be used wherever a unique identifier for the
29       local system is needed. However, it is recommended to use this ID as-is
30       only in trusted environments. In untrusted environments it is
31       recommended to derive an application specific ID from this machine ID,
32       in an irreversible (cryptographically secure) way. To make this easy
33       sd_id128_get_machine_app_specific() is provided, see below.
34
35       sd_id128_get_machine_app_specific() is similar to
36       sd_id128_get_machine(), but retrieves a machine ID that is specific to
37       the application that is identified by the indicated application ID. It
38       is recommended to use this function instead of sd_id128_get_machine()
39       when passing an ID to untrusted environments, in order to make sure
40       that the original machine ID may not be determined externally. This
41       way, the ID used by the application remains stable on a given machine,
42       but cannot be easily correlated with IDs used in other applications on
43       the same machine. The application-specific ID should be generated via a
44       tool like systemd-id128 new, and may be compiled into the application.
45       This function will return the same application-specific ID for each
46       combination of machine ID and application ID. Internally, this function
47       calculates HMAC-SHA256 of the application ID, keyed by the machine ID.
48
49       sd_id128_get_boot() returns the boot ID of the executing kernel. This
50       reads and parses the /proc/sys/kernel/random/boot_id file exposed by
51       the kernel. It is randomly generated early at boot and is unique for
52       every running kernel instance. See random(4) for more information. This
53       function also internally caches the returned ID to make this call a
54       cheap operation. It is recommended to use this ID as-is only in trusted
55       environments. In untrusted environments it is recommended to derive an
56       application specific ID using sd_id128_get_boot_app_specific(), see
57       below.
58
59       sd_id128_get_boot_app_specific() is analogous to
60       sd_id128_get_machine_app_specific() but returns an ID that changes
61       between boots. Some machines may be used for a long time without
62       rebooting, hence the boot ID may remain constant for a long time, and
63       has properties similar to the machine ID during that time.
64
65       sd_id128_get_invocation() returns the invocation ID of the currently
66       executed service. In its current implementation, this tries to read and
67       parse the following:
68
69       •   The $INVOCATION_ID environment variable that the service manager
70           sets when activating a service.
71
72       •   An entry in the kernel keyring that the system service manager sets
73           when activating a service.
74
75       See systemd.exec(5) for details. The ID is cached internally. In future
76       a different mechanism to determine the invocation ID may be added.
77
78       Note that sd_id128_get_machine_app_specific(), sd_id128_get_boot(),
79       sd_id128_get_boot_app_specific(), and sd_id128_get_invocation() always
80       return UUID Variant 1 Version 4 compatible IDs.  sd_id128_get_machine()
81       will also return a UUID Variant 1 Version 4 compatible ID on new
82       installations but might not on older. It is possible to convert the
83       machine ID non-reversibly into a UUID Variant 1 Version 4 compatible
84       one. For more information, see machine-id(5). It is hence guaranteed
85       that these functions will never return the ID consisting of all zero or
86       all one bits (SD_ID128_NULL, SD_ID128_ALLF) — with the possible
87       exception of sd_id128_get_machine(), as mentioned.
88
89       For more information about the "sd_id128_t" type see sd-id128(3).
90

RETURN VALUE

92       Those calls return 0 on success (in which case ret is filled in), or a
93       negative errno-style error code.
94
95   Errors
96       Returned errors may indicate the following problems:
97
98       -ENOENT
99           Returned by sd_id128_get_machine() and
100           sd_id128_get_machine_app_specific() when /etc/machine-id is
101           missing.
102
103       -ENOMEDIUM
104           Returned by sd_id128_get_machine() and
105           sd_id128_get_machine_app_specific() when /etc/machine-id is empty
106           or all zeros. Also returned by sd_id128_get_invocation() when the
107           invocation ID is all zeros.
108
109       -ENOPKG
110           Returned by sd_id128_get_machine() and
111           sd_id128_get_machine_app_specific() when the content of
112           /etc/machine-id is "uninitialized".
113
114       -ENOSYS
115           Returned by sd_id128_get_boot() and
116           sd_id128_get_boot_app_specific() when /proc/ is not mounted.
117
118       -ENXIO
119           Returned by sd_id128_get_invocation() if no invocation ID is set.
120
121       -EUCLEAN
122           Returned by any of the functions described here when the configured
123           value has invalid format.
124
125       -EPERM
126           Requested information could not be retrieved because of
127           insufficient permissions.
128

NOTES

130       Functions described here are available as a shared library, which can
131       be compiled against and linked to with the libsystemd pkg-config(1)
132       file.
133
134       The code described here uses getenv(3), which is declared to be not
135       multi-thread-safe. This means that the code calling the functions
136       described here must not call setenv(3) from a parallel thread. It is
137       recommended to only do calls to setenv() from an early phase of the
138       program when no other threads have been started.
139

EXAMPLES

141       Example 1. Application-specific machine ID
142
143       First, generate the application ID:
144
145           $ systemd-id128 -p new
146           As string:
147           c273277323db454ea63bb96e79b53e97
148
149           As UUID:
150           c2732773-23db-454e-a63b-b96e79b53e97
151
152           As man:sd-id128(3) macro:
153           #define MESSAGE_XYZ SD_ID128_MAKE(c2,73,27,73,23,db,45,4e,a6,3b,b9,6e,79,b5,3e,97)
154           ...
155
156       Then use the new identifier in an example application:
157
158           /* SPDX-License-Identifier: MIT-0 */
159
160           #include <stdio.h>
161           #include <systemd/sd-id128.h>
162
163           #define OUR_APPLICATION_ID SD_ID128_MAKE(c2,73,27,73,23,db,45,4e,a6,3b,b9,6e,79,b5,3e,97)
164
165           int main(int argc, char *argv[]) {
166             sd_id128_t id;
167             sd_id128_get_machine_app_specific(OUR_APPLICATION_ID, &id);
168             printf("Our application ID: " SD_ID128_FORMAT_STR "\n", SD_ID128_FORMAT_VAL(id));
169             return 0;
170           }
171

NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

NOTES

EXAMPLES

SEE ALSO