Description¶

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¶

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¶

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¶

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¶

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)