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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | EXAMPLES | HISTORY | SEE ALSO | COLOPHON |
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SD_JOURN...RY_UNIQUE(3) sd_journal_query_unique SD_JOURN...RY_UNIQUE(3)
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
#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);
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.
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()
does not 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.
All functions listed here are thread-agnostic and only a single
specific thread may operate on a given object during its entire
lifetime. It is safe to allocate multiple independent objects and
use each from a specific thread in parallel. However, it is 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
do not 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.
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;
}
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.
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)
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a
bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) 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
man-pages@man7.org
systemd 258~rc2 SD_JOURN...RY_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)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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