sd_journal_enumerate_fields(3) — Linux manual page


SD_JOUR...E_FIELDS(3)  sd_journal_enumerate_fields SD_JOUR...E_FIELDS(3)

NAME         top

       sd_journal_enumerate_fields, sd_journal_restart_fields,
       SD_JOURNAL_FOREACH_FIELD - Read used field names from the journal

SYNOPSIS         top

       #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);

DESCRIPTION         top

       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_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

       The SD_JOURNAL_FOREACH_FIELD() macro may be used as a handy
       wrapper around sd_journal_restart_fields() and

       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

RETURN VALUE         top

       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.

NOTES         top

       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         top

       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) {
               errno = -r;
               fprintf(stderr, "Failed to open journal: %m\n");
               return 1;
             SD_JOURNAL_FOREACH_FIELD(j, field)
               printf("%s\n", field);
             return 0;

HISTORY         top

       sd_journal_enumerate_fields(), sd_journal_restart_fields(), and
       SD_JOURNAL_FOREACH_FIELD() were added in version 229.

SEE ALSO         top

       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)

COLOPHON         top

       This page is part of the systemd (systemd system and service
       manager) project.  Information about the project can be found at
       ⟨⟩.  If you have
       a bug report for this manual page, see
       This page was obtained from the project's upstream Git repository
       ⟨⟩ on 2023-12-22.  (At that
       time, the date of the most recent commit that was found in the
       repository was 2023-12-22.)  If you discover any rendering
       problems in this HTML version of the page, or you believe there
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       (which is not part of the original manual page), send a mail to

systemd 255                                        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)