sd_journal_restart_fields(3) — Linux manual page



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_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

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

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.

       These APIs are implemented as a shared library, which can be compiled
       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.

           #include <stdio.h>
           #include <string.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);
                   return 0;

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 2020-11-01.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-11-01.)  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 im‐
       provements to the information in this COLOPHON (which is not part of
       the original manual page), send a mail to

systemd 247                                   SD_JOURNAL_ENUMERATE_FIELDS(3)

Pages that refer to this page: 30-systemd-environment-d-generator(7)systemd.index(7)