systemd Developer Lennart Poettering lennart@poettering.net sd_journal_query_unique 3 sd_journal_query_unique sd_journal_enumerate_unique sd_journal_restart_unique SD_JOURNAL_FOREACH_UNIQUE Read unique data fields from the journal #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 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-fields7. 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. 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. 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-config1 file. 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); sd_journal_close(j); return 0; } systemd1, systemd.journal-fields7, sd-journal3, sd_journal_open3, sd_journal_get_data3, sd_journal_add_match3