SD_JOURNAL_QUERY_UNIQUE(3) sd_journal_query_unique SD_JOURNAL_QUERY_UNIQUE(3)
NAME
sd_journal_query_unique, sd_journal_enumerate_unique, sd_journal_restart_unique, SD_JOURNAL_FOREACH_UNIQUE - Read unique data fields from
the journal
SYNOPSIS
#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
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_set_data_threshold().
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
sd_journal_enumerate_unique().
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.
RETURN VALUE
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
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-journal pkg-config(1) file.
EXAMPLES
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
", strerror(-r));
return 1;
}
r = sd_journal_query_unique(j, "_SYSTEMD_UNIT");
if (r < 0) {
fprintf(stderr, "Failed to query journal: %s
", strerror(-r));
return 1;
}
SD_JOURNAL_FOREACH_UNIQUE(j, d, l)
printf("%.*s
", (int) l, (const char*) d);
sd_journal_close(j);
return 0;
}
SEE ALSO
systemd(1), systemd.journal-fields(7), sd-journal(3), sd_journal_open(3), sd_journal_get_data(3), sd_journal_add_match(3)
systemd 208 SD_JOURNAL_QUERY_UNIQUE(3)