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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | HISTORY | SEE ALSO | COLOPHON |
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SD_JOURNAL_GET_SEQNUM(3) sd_journal_get_seqnum SD_JOURNAL_GET_SEQNUM(3)
sd_journal_get_seqnum - Read sequence number from the current
journal entry
#include <systemd/sd-journal.h>
int sd_journal_get_seqnum(sd_journal *j, uint64_t *ret_seqnum,
sd_id128_t *ret_seqnum_id);
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.
sd_journal_get_seqnum() returns 0 on success or a negative
errno-style error code..
All functions listed here are thread-agnostic and only a single
specific thread may operate on a given object during its entire
lifetime. It is safe to allocate multiple independent objects and
use each from a specific thread in parallel. However, it is 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
do not 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.
sd_journal_get_seqnum() was added in version 254.
systemd(1), sd-journal(3), sd_journal_open(3), sd_journal_next(3),
sd_journal_get_data(3), sd_journal_get_monotonic_usec(3)
This page is part of the systemd (systemd system and service
manager) project. Information about the project can be found at
⟨http://www.freedesktop.org/wiki/Software/systemd⟩. If you have a
bug report for this manual page, see
⟨http://www.freedesktop.org/wiki/Software/systemd/#bugreports⟩.
This page was obtained from the project's upstream Git repository
⟨https://github.com/systemd/systemd.git⟩ on 2025-08-11. (At that
time, the date of the most recent commit that was found in the
repository was 2025-08-11.) 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
man-pages@man7.org
systemd 258~rc2 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)
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HTML rendering created 2025-09-06 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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