Provided by: libsystemd-dev_256.5-2ubuntu4_amd64 
NAME
sd_journal_query_unique, sd_journal_enumerate_unique,
sd_journal_enumerate_available_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_available_unique(sd_journal *j, const void **data,
size_t *length);
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), but any field can be
specified. 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() and sd_journal_enumerate_available_unique(). Invoking one of
those calls 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 object, plus a
pair of pointers to pointer/size variables where the data object and its size shall be
stored. 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() and only the initial part of
the field up to the threshold is returned. An error is returned for fields which cannot be
retrieved. See the error list below for details.
sd_journal_enumerate_available_unique() is similar to sd_journal_enumerate_unique(), but
silently skips any fields which may be valid, but are too large or not supported by
current implementation.
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_available_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.
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
sd_journal_query_unique() returns 0 on success or a negative errno-style error code.
sd_journal_enumerate_unique() and sd_journal_query_available_unique() return a positive
integer if the next field data has been read, 0 when no more fields remain, or a negative
errno-style error code. sd_journal_restart_unique() doesn't return anything.
Errors
Returned errors may indicate the following problems:
-EINVAL
One of the required parameters is NULL or invalid.
Added in version 246.
-ECHILD
The journal object was created in a different process, library or module instance.
Added in version 246.
-EADDRNOTAVAIL
The read pointer is not positioned at a valid entry; sd_journal_next(3) or a related
call has not been called at least once.
Added in version 246.
-ENOENT
The current entry does not include the specified field.
Added in version 246.
-ENOBUFS
A compressed entry is too large.
Added in version 246.
-E2BIG
The data field is too large for this computer architecture (e.g. above 4 GB on a
32-bit architecture).
Added in version 246.
-EPROTONOSUPPORT
The journal is compressed with an unsupported method or the journal uses an
unsupported feature.
Added in version 246.
-EBADMSG
The journal is corrupted (possibly just the entry being iterated over).
Added in version 246.
-EIO
An I/O error was reported by the kernel.
Added in version 246.
NOTES
All functions listed here are thread-agnostic and only a single specific thread may
operate on a given object during its entire lifetime. It's safe to allocate multiple
independent objects and use each from a specific thread in parallel. However, it's 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't operate on it at the very same time.
Functions described here are available as a shared library, which can be compiled against
and linked to with the libsystemd pkg-config(1) file.
EXAMPLES
Use the SD_JOURNAL_FOREACH_UNIQUE() macro to iterate through all values a field of the
journal can take (and which can be accessed on the given architecture and are not
compressed with an unsupported mechanism). The following example lists all unit names
referenced in the journal:
/* SPDX-License-Identifier: MIT-0 */
#include <errno.h>
#include <stdio.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;
}
HISTORY
sd_journal_query_unique(), sd_journal_enumerate_unique(), sd_journal_restart_unique(), and
SD_JOURNAL_FOREACH_UNIQUE() were added in version 195.
sd_journal_enumerate_available_unique() was added in version 246.
SEE ALSO
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)