sd_journal_get_seqnum(3) — Linux manual page


SD_JOURNAL_GET_SEQNUM(3)  sd_journal_get_seqnum SD_JOURNAL_GET_SEQNUM(3)

NAME         top

       sd_journal_get_seqnum - Read sequence number from the current
       journal entry

SYNOPSIS         top

       #include <systemd/sd-journal.h>

       int sd_journal_get_seqnum(sd_journal *j, uint64_t *ret_seqnum,
                                 sd_id128_t *ret_seqnum_id);

DESCRIPTION         top

       sd_journal_get_seqnum() returns the sequence number of the
       current journal entry. It takes three arguments: the journal
       context object, a pointer to a 64-bit unsigned integer to store
       the sequence number in, and a buffer to return the 128-bit
       sequence number ID in.

       When writing journal entries to disk each systemd-journald
       instance will number them sequentially, starting from 1 for the
       first entry written after subsystem initialization. Each such
       series of sequence numbers is associated with a 128-bit sequence
       number ID which is initialized randomly, once at systemd-journal
       initialization. Thus, while multiple instances of
       systemd-journald will assign the same sequence numbers to their
       written journal entries, they will have a distinct sequence
       number IDs. The sequence number is assigned at the moment of
       writing the entry to disk. If log entries are rewritten (for
       example because the volatile logs from /run/log/ are flushed to
       /var/log/ via systemd-journald-flush.service) they will get new
       sequence numbers assigned.

       Sequence numbers may be used to order entries (entries associated
       with the same sequence number ID and lower sequence numbers
       should be ordered chronologically before those with higher
       sequence numbers), and to detect lost entries. Note that journal
       service instances typically write to multiple journal files in
       parallel (for example because SplitMode= is used), in which case
       each journal file will only contain a subset of the sequence
       numbers. To recover the full stream of journal entries the files
       must be combined ("interleaved"), a process that primarily relies
       on the sequence numbers. When journal files are rotated (due to
       size or time limits), the series of sequence numbers is continued
       in the replacement files. All journal files generated from the
       same journal instance will carry the same sequence number ID.

       As the sequence numbers are assigned at the moment of writing the
       journal entries to disk they do not exist if storage is disabled
       via SplitMode=.

       The ret_seqnum and ret_seqnum_id parameters may be specified as
       NULL in which case the relevant data is not returned (but the
       call will otherwise succeed).

       Note that these functions will not work before sd_journal_next(3)
       (or related call) has been called at least once, in order to
       position the read pointer at a valid entry.

RETURN VALUE         top

       sd_journal_get_seqnum() returns 0 on success or a negative
       errno-style error code..

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.

HISTORY         top

       sd_journal_get_seqnum() was added in version 254.

SEE ALSO         top

       systemd(1), sd-journal(3), sd_journal_open(3),
       sd_journal_next(3), sd_journal_get_data(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
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       (which is not part of the original manual page), send a mail to

systemd 255                                     SD_JOURNAL_GET_SEQNUM(3)

Pages that refer to this page: sd_journal_get_realtime_usec(3)systemd.directives(7)systemd.index(7)systemd.journal-fields(7)