x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
SD_JOURNAL_GET_SEQNUM(3) sd_journal_get_seqnum SD_JOURNAL_GET_SEQNUM(3)
NAME
sd_journal_get_seqnum - Read sequence number from the current journal
entry
SYNOPSIS
#include <systemd/sd-journal.h>
int sd_journal_get_seqnum(sd_journal *j, uint64_t *ret_seqnum,
sd_id128_t *ret_seqnum_id);
DESCRIPTION
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
sd_journal_get_seqnum() returns 0 on success or a negative errno-style
error code..
NOTES
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.
SEE ALSO
systemd(1), sd-journal(3), sd_journal_open(3), sd_journal_next(3),
sd_journal_get_data(3), sd_journal_get_monotonic_usec(3)
systemd 254 SD_JOURNAL_GET_SEQNUM(3)
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