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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | EXAMPLES | HISTORY | SEE ALSO | COLOPHON |
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SD_JOUR...E_FIELDS(3) sd_journal_enumerate_fields SD_JOUR...E_FIELDS(3)
sd_journal_enumerate_fields, sd_journal_restart_fields,
SD_JOURNAL_FOREACH_FIELD - Read used field names from the journal
#include <systemd/sd-journal.h>
int sd_journal_enumerate_fields(sd_journal *j,
const char **field);
void sd_journal_restart_fields(sd_journal *j);
SD_JOURNAL_FOREACH_FIELD(sd_journal *j, const char *field);
sd_journal_enumerate_fields() may be used to iterate through all
field names used in the opened journal files. On each invocation
the next field name is returned. The order of the returned field
names is not defined. It takes two arguments: the journal context
object, plus a pointer to a constant string pointer where the
field name is stored in. The returned data is in a read-only
memory map and is only valid until the next invocation of
sd_journal_enumerate_fields(). Note that this call is subject to
the data field size threshold as controlled by
sd_journal_set_data_threshold().
sd_journal_restart_fields() resets the field name enumeration
index to the beginning of the list. The next invocation of
sd_journal_enumerate_fields() will return the first field name
again.
The SD_JOURNAL_FOREACH_FIELD() macro may be used as a handy
wrapper around sd_journal_restart_fields() and
sd_journal_enumerate_fields().
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 retrieve the possible values a specific field can take use
sd_journal_query_unique(3).
sd_journal_enumerate_fields() returns a positive integer if the
next field name has been read, 0 when no more field names are
known, or a negative errno-style error code.
sd_journal_restart_fields() returns nothing.
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_FIELD() macro to iterate through all
field names in use in the current 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 char *field;
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;
}
SD_JOURNAL_FOREACH_FIELD(j, field)
printf("%s\n", field);
sd_journal_close(j);
return 0;
}
sd_journal_enumerate_fields(), sd_journal_restart_fields(), and
SD_JOURNAL_FOREACH_FIELD() were added in version 229.
systemd(1), systemd.journal-fields(7), sd-journal(3),
sd_journal_open(3), sd_journal_query_unique(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_JOUR...E_FIELDS(3)
Pages that refer to this page: sd-journal(3), sd_journal_query_unique(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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