SD-ID128(3)                       sd-id128                       SD-ID128(3)

NAME         top

       sd-id128, sd_id128_t, SD_ID128_MAKE, SD_ID128_MAKE_STR,
       SD_ID128_FORMAT_VAL, sd_id128_equal, sd_id128_is_null - APIs for
       processing 128-bit IDs

SYNOPSIS         top

       #include <systemd/sd-id128.h>

       pkg-config --cflags --libs libsystemd

DESCRIPTION         top

       sd-id128.h provides APIs to process and generate 128-bit ID values.
       The 128-bit ID values processed and generated by these APIs are a
       generalization of OSF UUIDs as defined by RFC 4122[1] but use a
       simpler string format. These functions impose no structure on the
       used IDs, much unlike OSF UUIDs or Microsoft GUIDs, but are fully
       compatible with those types of IDs.

       See sd_id128_to_string(3), sd_id128_randomize(3) and
       sd_id128_get_machine(3) for more information about the implemented

       A 128-bit ID is implemented as the following union type:

           typedef union sd_id128 {
                   uint8_t bytes[16];
                   uint64_t qwords[2];
           } sd_id128_t;

       This union type allows accessing the 128-bit ID as 16 separate bytes
       or two 64-bit words. It is generally safer to access the ID
       components by their 8-bit array to avoid endianness issues. This
       union is intended to be passed call-by-value (as opposed to
       call-by-reference) and may be directly manipulated by clients.

       A couple of macros are defined to denote and decode 128-bit IDs:

       SD_ID128_MAKE() may be used to denote a constant 128-bit ID in source
       code. A commonly used idiom is to assign a name to a 128-bit ID using
       this macro:

           #define SD_MESSAGE_COREDUMP SD_ID128_MAKE(fc,2e,22,bc,6e,e6,47,b6,b9,07,29,ab,34,a2,50,b1)

       SD_ID128_NULL may be used to refer to the 128bit ID consisting of
       only NUL bytes.

       SD_ID128_MAKE_STR() is similar to SD_ID128_MAKE(), but creates a
       const char* expression that can be conveniently used in message
       formats and such:

           #include <stdio.h>
           #define SD_MESSAGE_COREDUMP_STR SD_ID128_MAKE_STR(fc,2e,22,bc,6e,e6,47,b6,b9,07,29,ab,34,a2,50,b1)

           int main(int argc, char **argv) {
                   puts("Match for coredumps: MESSAGE_ID=" SD_MESSAGE_COREDUMP_STR);

       SD_ID128_CONST_STR() may be used to convert constant 128-bit IDs into
       constant strings for output. The following example code will output
       the string "fc2e22bc6ee647b6b90729ab34a250b1":

           int main(int argc, char *argv[]) {
                   puts("Match for coredumps: %s", SD_ID128_CONST_STR(SD_MESSAGE_COREDUMP));

       SD_ID128_FORMAT_STR() and SD_ID128_FORMAT_VAL() may be used to format
       a 128-bit ID in a printf(3) format string, as shown in the following

           int main(int argc, char *argv[]) {
                   sd_id128_t id;
                   id = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07);
                   printf("The ID encoded in this C file is " SD_ID128_FORMAT_STR ".\n", SD_ID128_FORMAT_VAL(id));
                   return 0;

       Use sd_id128_equal() to compare two 128-bit IDs:

           int main(int argc, char *argv[]) {
                   sd_id128_t a, b, c;
                   a = SD_ID128_MAKE(ee,89,be,71,bd,6e,43,d6,91,e6,c5,5d,eb,03,02,07);
                   b = SD_ID128_MAKE(f2,28,88,9c,5f,09,44,15,9d,d7,04,77,58,cb,e7,3e);
                   c = a;
                   assert(sd_id128_equal(a, c));
                   assert(!sd_id128_equal(a, b));
                   return 0;

       Use sd_id128_is_null() to check if an 128bit ID consists of only NUL

           int main(int argc, char *argv[]) {

       Note that new, randomized IDs may be generated with journalctl(1)'s
       --new-id128 option.

NOTES         top

       These APIs are implemented as a shared library, which can be compiled
       and linked to with the libsystemd pkg-config(1) file.

SEE ALSO         top

       systemd(1), sd_id128_to_string(3), sd_id128_randomize(3),
       sd_id128_get_machine(3), printf(3), journalctl(1), sd-journal(7),
       pkg-config(1), machine-id(5)

NOTES         top

        1. RFC 4122

COLOPHON         top

       This page is part of the systemd (systemd system and service manager)
       project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug
       report for this manual page, see
       ⟨⟩.  This
       page was obtained from the project's upstream Git repository
       ⟨⟩ on 2018-02-02.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2018-02-02.)  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

systemd 234                                                      SD-ID128(3)

Pages that refer to this page: sd_id128_get_machine(3)sd_id128_randomize(3)sd_id128_to_string(3)sd-journal(3)machine-id(5)systemd.directives(7)systemd.index(7)