NAME         top

       sd_journal_query_unique, sd_journal_enumerate_unique,
       sd_journal_restart_unique, SD_JOURNAL_FOREACH_UNIQUE - Read unique
       data fields from the journal

SYNOPSIS         top

       #include <systemd/sd-journal.h>

       int sd_journal_query_unique(sd_journal *j, const char *field);

       int sd_journal_enumerate_unique(sd_journal *j, const void **data,
                                       size_t *length);

       void sd_journal_restart_unique(sd_journal *j);

       SD_JOURNAL_FOREACH_UNIQUE(sd_journal *j, const void *data,
                                 size_t length);

DESCRIPTION         top

       sd_journal_query_unique() queries the journal for all unique values
       the specified field can take. It takes two arguments: the journal to
       query and the field name to look for. Well-known field names are
       listed on systemd.journal-fields(7). Field names must be specified
       without a trailing '='. After this function has been executed
       successfully the field values may be queried using
       sd_journal_enumerate_unique(). Invoking this call a second time will
       change the field name being queried and reset the enumeration index
       to the first field value that matches.

       sd_journal_enumerate_unique() may be used to iterate through all data
       fields which match the previously selected field name as set with
       sd_journal_query_unique(). On each invocation the next field data
       matching the field name is returned. The order of the returned data
       fields is not defined. It takes three arguments: the journal context
       object, plus a pair of pointers to pointer/size variables where the
       data object and its size shall be stored in. The returned data is in
       a read-only memory map and is only valid until the next invocation of
       sd_journal_enumerate_unique(). Note that the data returned will be
       prefixed with the field name and '='. Note that this call is subject
       to the data field size threshold as controlled by

       sd_journal_restart_unique() resets the data enumeration index to the
       beginning of the list. The next invocation of
       sd_journal_enumerate_unique() will return the first field data
       matching the field name again.

       Note that the SD_JOURNAL_FOREACH_UNIQUE() macro may be used as a
       handy wrapper around sd_journal_restart_unique() and

       Note that these functions currently are not influenced by matches set
       with sd_journal_add_match() but this might change in a later version
       of this software.

       To enumerate all field names currently in use (and thus all suitable
       field parameters for sd_journal_query_unique()), use the
       sd_journal_enumerate_fields(3) call.

RETURN VALUE         top

       sd_journal_query_unique() returns 0 on success or a negative
       errno-style error code.  sd_journal_enumerate_unique() returns a
       positive integer if the next field data has been read, 0 when no more
       fields are known, or a negative errno-style error code.
       sd_journal_restart_unique() returns nothing.

NOTES         top

       All functions listed here are thread-agnostic and only a single
       thread may operate on a given sd_journal object.

       The sd_journal_query_unique(), sd_journal_enumerate_unique() and
       sd_journal_restart_unique() interfaces are available as a shared
       library, which can be compiled and linked to with the
       libsystemd pkg-config(1) file.

EXAMPLES         top

       Use the SD_JOURNAL_FOREACH_UNIQUE macro to iterate through all values
       a field of the journal can take. The following example lists all unit
       names referenced in the journal:

           #include <stdio.h>
           #include <string.h>
           #include <systemd/sd-journal.h>

           int main(int argc, char *argv[]) {
                   sd_journal *j;
                   const void *d;
                   size_t l;
                   int r;

                   r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY);
                   if (r < 0) {
                           fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
                           return 1;
                   r = sd_journal_query_unique(j, "_SYSTEMD_UNIT");
                   if (r < 0) {
                           fprintf(stderr, "Failed to query journal: %s\n", strerror(-r));
                           return 1;
                   SD_JOURNAL_FOREACH_UNIQUE(j, d, l)
                           printf("%.*s\n", (int) l, (const char*) d);
                   return 0;

SEE ALSO         top

       systemd(1), systemd.journal-fields(7), sd-journal(3),
       sd_journal_open(3), sd_journal_enumerate_fields(3),
       sd_journal_get_data(3), sd_journal_add_match(3)

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 2019-05-09.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2019-05-09.)  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_JOURNAL_QUERY_UNIQUE(3)

Pages that refer to this page: sd-journal(3)sd_journal_enumerate_fields(3)sd_journal_get_data(3)systemd.directives(7)systemd.index(7)