sd-journal(3) — Linux manual page

SD-JOURNAL(3)                   sd-journal                  SD-JOURNAL(3)

NAME         top

       sd-journal - APIs for submitting and querying log entries to and
       from the journal

SYNOPSIS         top

       #include <systemd/sd-journal.h>

       pkg-config --cflags --libs libsystemd

DESCRIPTION         top

       sd-journal.h is part of libsystemd(3) and provides APIs to submit
       and query log entries. The APIs exposed act both as client for the
       systemd-journald.service(8) journal service and as parser for the
       journal files on disk.

       See sd_journal_print(3), sd_journal_stream_fd(3),
       sd_journal_open(3), sd_journal_next(3),
       sd_journal_get_realtime_usec(3), sd_journal_add_match(3),
       sd_journal_seek_head(3), sd_journal_enumerate_fields(3),
       sd_journal_get_cursor(3), sd_journal_get_cutoff_realtime_usec(3),
       sd_journal_get_cutoff_monotonic_usec(3), sd_journal_get_usage(3),
       sd_journal_get_catalog(3), sd_journal_get_fd(3),
       sd_journal_has_runtime_files(3) and
       sd_journal_has_persistent_files(3) for more information about the
       functions implemented.

       Command line access for submitting entries to the journal is
       available with the systemd-cat(1) tool. Command line access for
       querying entries from the journal is available with the
       journalctl(1) tool.

THREAD SAFETY         top

       Functions that operate on sd_journal objects are thread agnostic —
       given sd_journal pointer may only be used from one specific thread
       at all times (and it has to be the very same one during the entire
       lifetime of the object), but multiple, independent threads may use
       multiple, independent objects safely. Other functions — those that
       are used to send entries to the journal, like sd_journal_print(3)
       and similar, or those that are used to retrieve global information
       like sd_journal_stream_fd(3) and
       sd_journal_get_catalog_for_message_id(3) — are fully thread-safe
       and may be called from multiple threads in parallel.

OPTIONAL DEPENDENCIES         top

       Depending on which build-time options are enabled, functions that
       operate on sd_journal objects might cause optional shared
       libraries to be dynamically loaded via dlopen(3), such as
       decompression libraries (xz, lz4, zstd) or cryptographic libraries
       (gcrypt).

NOTES         top

       Functions described here are available as a shared library, which
       can be compiled against and linked to with the
       libsystemd pkg-config(1) file.

       The code described here uses getenv(3), which is declared to be
       not multi-thread-safe. This means that the code calling the
       functions described here must not call setenv(3) from a parallel
       thread. It is recommended to only do calls to setenv() from an
       early phase of the program when no other threads have been
       started.

SEE ALSO         top

       systemd(1), sd_journal_print(3), sd_journal_stream_fd(3),
       sd_journal_open(3), sd_journal_next(3), sd_journal_get_data(3),
       sd_journal_get_realtime_usec(3), sd_journal_add_match(3),
       sd_journal_seek_head(3), sd_journal_enumerate_fields(3),
       sd_journal_get_cursor(3), sd_journal_get_cutoff_realtime_usec(3),
       sd_journal_get_cutoff_monotonic_usec(3), sd_journal_get_usage(3),
       sd_journal_get_fd(3), sd_journal_query_unique(3),
       sd_journal_get_catalog(3), sd_journal_has_runtime_files(3),
       sd_journal_has_persistent_files(3), journalctl(1), sd-id128(3),
       pkg-config(1)

COLOPHON         top

       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
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       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(3)

Pages that refer to this page: libsystemd(3),  sd-id128(3),  sd_journal_add_match(3),  sd_journal_enumerate_fields(3),  sd_journal_get_catalog(3),  sd_journal_get_cursor(3),  sd_journal_get_cutoff_realtime_usec(3),  sd_journal_get_data(3),  sd_journal_get_fd(3),  sd_journal_get_realtime_usec(3),  sd_journal_get_seqnum(3),  sd_journal_get_usage(3),  sd_journal_has_runtime_files(3),  sd_journal_next(3),  sd_journal_open(3),  sd_journal_print(3),  sd_journal_query_unique(3),  sd_journal_seek_head(3),  sd_journal_stream_fd(3),  systemd.exec(5),  systemd.directives(7),  systemd.index(7),  systemd.journal-fields(7),  systemd-coredump(8),  systemd-journald.service(8)

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