'\" t .TH "SD_JOURNAL_QUERY_UNIQUE" "3" "" "systemd 241" "sd_journal_query_unique" .\" ----------------------------------------------------------------- .\" * Define some portability stuff .\" ----------------------------------------------------------------- .\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .\" http://bugs.debian.org/507673 .\" http://lists.gnu.org/archive/html/groff/2009-02/msg00013.html .\" ~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~ .ie \n(.g .ds Aq \(aq .el .ds Aq ' .\" ----------------------------------------------------------------- .\" * set default formatting .\" ----------------------------------------------------------------- .\" disable hyphenation .nh .\" disable justification (adjust text to left margin only) .ad l .\" ----------------------------------------------------------------- .\" * MAIN CONTENT STARTS HERE * .\" ----------------------------------------------------------------- .SH "NAME" sd_journal_query_unique, sd_journal_enumerate_unique, sd_journal_restart_unique, SD_JOURNAL_FOREACH_UNIQUE \- Read unique data fields from the journal .SH "SYNOPSIS" .sp .ft B .nf #include .fi .ft .HP \w'int\ sd_journal_query_unique('u .BI "int sd_journal_query_unique(sd_journal\ *" "j" ", const\ char\ *" "field" ");" .HP \w'int\ sd_journal_enumerate_unique('u .BI "int sd_journal_enumerate_unique(sd_journal\ *" "j" ", const\ void\ **" "data" ", size_t\ *" "length" ");" .HP \w'void\ sd_journal_restart_unique('u .BI "void sd_journal_restart_unique(sd_journal\ *" "j" ");" .HP \w'SD_JOURNAL_FOREACH_UNIQUE('u .BI "SD_JOURNAL_FOREACH_UNIQUE(sd_journal\ *" "j" ", const\ void\ *" "data" ", size_t\ " "length" ");" .SH "DESCRIPTION" .PP \fBsd_journal_query_unique()\fR 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 \fBsystemd.journal-fields\fR(7)\&. Field names must be specified without a trailing \*(Aq=\*(Aq\&. After this function has been executed successfully the field values may be queried using \fBsd_journal_enumerate_unique()\fR\&. 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\&. .PP \fBsd_journal_enumerate_unique()\fR may be used to iterate through all data fields which match the previously selected field name as set with \fBsd_journal_query_unique()\fR\&. 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 \fBsd_journal_enumerate_unique()\fR\&. Note that the data returned will be prefixed with the field name and \*(Aq=\*(Aq\&. Note that this call is subject to the data field size threshold as controlled by \fBsd_journal_set_data_threshold()\fR\&. .PP \fBsd_journal_restart_unique()\fR resets the data enumeration index to the beginning of the list\&. The next invocation of \fBsd_journal_enumerate_unique()\fR will return the first field data matching the field name again\&. .PP Note that the \fBSD_JOURNAL_FOREACH_UNIQUE()\fR macro may be used as a handy wrapper around \fBsd_journal_restart_unique()\fR and \fBsd_journal_enumerate_unique()\fR\&. .PP Note that these functions currently are not influenced by matches set with \fBsd_journal_add_match()\fR but this might change in a later version of this software\&. .PP To enumerate all field names currently in use (and thus all suitable field parameters for \fBsd_journal_query_unique()\fR), use the \fBsd_journal_enumerate_fields\fR(3) call\&. .SH "RETURN VALUE" .PP \fBsd_journal_query_unique()\fR returns 0 on success or a negative errno\-style error code\&. \fBsd_journal_enumerate_unique()\fR 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\&. \fBsd_journal_restart_unique()\fR returns nothing\&. .SH "NOTES" .PP All functions listed here are thread\-agnostic and only a single specific thread may operate on a given object during its entire lifetime\&. It\*(Aqs safe to allocate multiple independent objects and use each from a specific thread in parallel\&. However, it\*(Aqs not safe to allocate such an object in one thread, and operate or free it from any other, even if locking is used to ensure these threads don\*(Aqt operate on it at the very same time\&. .PP These APIs are implemented as a shared library, which can be compiled and linked to with the \fBlibsystemd\fR\ \&\fBpkg-config\fR(1) file\&. .SH "EXAMPLES" .PP Use the \fBSD_JOURNAL_FOREACH_UNIQUE\fR macro to iterate through all values a field of the journal can take\&. The following example lists all unit names referenced in the journal: .sp .if n \{\ .RS 4 .\} .nf #include #include #include 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\en", strerror(\-r)); return 1; } r = sd_journal_query_unique(j, "_SYSTEMD_UNIT"); if (r < 0) { fprintf(stderr, "Failed to query journal: %s\en", strerror(\-r)); return 1; } SD_JOURNAL_FOREACH_UNIQUE(j, d, l) printf("%\&.*s\en", (int) l, (const char*) d); sd_journal_close(j); return 0; } .fi .if n \{\ .RE .\} .SH "SEE ALSO" .PP \fBsystemd\fR(1), \fBsystemd.journal-fields\fR(7), \fBsd-journal\fR(3), \fBsd_journal_open\fR(3), \fBsd_journal_enumerate_fields\fR(3), \fBsd_journal_get_data\fR(3), \fBsd_journal_add_match\fR(3)