sd_journal_foreach(3) — Linux manual page


SD_JOURNAL_NEXT(3)             sd_journal_next            SD_JOURNAL_NEXT(3)

NAME         top

       sd_journal_next, sd_journal_previous, sd_journal_next_skip,
       sd_journal_previous_skip, SD_JOURNAL_FOREACH,
       SD_JOURNAL_FOREACH_BACKWARDS - Advance or set back the read pointer
       in the journal

SYNOPSIS         top

       #include <systemd/sd-journal.h>

       int sd_journal_next(sd_journal *j);

       int sd_journal_previous(sd_journal *j);

       int sd_journal_next_skip(sd_journal *j, uint64_t skip);

       int sd_journal_previous_skip(sd_journal *j, uint64_t skip);

       SD_JOURNAL_FOREACH(sd_journal *j);

       SD_JOURNAL_FOREACH_BACKWARDS(sd_journal *j);

DESCRIPTION         top

       sd_journal_next() advances the read pointer into the journal by one
       entry. The only argument taken is a journal context object as
       allocated via sd_journal_open(3). After successful invocation the
       entry may be read with functions such as sd_journal_get_data(3).

       Similarly, sd_journal_previous() sets the read pointer back one

       sd_journal_next_skip() and sd_journal_previous_skip() advance/set
       back the read pointer by multiple entries at once, as specified in
       the skip parameter.

       The journal is strictly ordered by reception time, and hence
       advancing to the next entry guarantees that the entry then pointing
       to is later in time than then previous one, or has the same

       Note that sd_journal_get_data(3) and related calls will fail unless
       sd_journal_next() has been invoked at least once in order to position
       the read pointer on a journal entry.

       Note that the SD_JOURNAL_FOREACH() macro may be used as a wrapper
       around sd_journal_seek_head(3) and sd_journal_next() in order to make
       iterating through the journal easier. See below for an example.
       Similarly, SD_JOURNAL_FOREACH_BACKWARDS() may be used for iterating
       the journal in reverse order.

RETURN VALUE         top

       The four calls return the number of entries advanced/set back on
       success or a negative errno-style error code. When the end or
       beginning of the journal is reached, a number smaller than requested
       is returned. More specifically, if sd_journal_next() or
       sd_journal_previous() reach the end/beginning of the journal they
       will return 0, instead of 1 when they are successful. This should be
       considered an EOF marker.

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

       Iterating through the journal:

           #include <stdio.h>
           #include <string.h>
           #include <systemd/sd-journal.h>

           int main(int argc, char *argv[]) {
             int r;
             sd_journal *j;
             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(j) {
               const char *d;
               size_t l;

               r = sd_journal_get_data(j, "MESSAGE", (const void **)&d, &l);
               if (r < 0) {
                 fprintf(stderr, "Failed to read message field: %s\n", strerror(-r));

               printf("%.*s\n", (int) l, d);
             return 0;

SEE ALSO         top

       systemd(1), sd-journal(3), sd_journal_open(3),
       sd_journal_get_data(3), sd_journal_get_realtime_usec(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 2020-08-13.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-08-11.)  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

systemd 246                                               SD_JOURNAL_NEXT(3)