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NAME |SYNOPSIS |DESCRIPTION |RETURN VALUE |NOTES |EXAMPLES |HISTORY |SEE ALSO |COLOPHON | |
SD_JOURNAL_GET_DATA(3) sd_journal_get_dataSD_JOURNAL_GET_DATA(3)sd_journal_get_data, sd_journal_enumerate_data, sd_journal_enumerate_available_data, sd_journal_restart_data, SD_JOURNAL_FOREACH_DATA, sd_journal_set_data_threshold, sd_journal_get_data_threshold - Read data fields from the current journal entry
#include <systemd/sd-journal.h>int sd_journal_get_data(sd_journal *j, const char *field,const void **data, size_t *length);int sd_journal_enumerate_data(sd_journal *j, const void **data,size_t *length);int sd_journal_enumerate_available_data(sd_journal *j,const void **data,size_t *length);void sd_journal_restart_data(sd_journal *j);SD_JOURNAL_FOREACH_DATA(sd_journal *j, const void *data,size_tlength);int sd_journal_set_data_threshold(sd_journal *j, size_tsz);int sd_journal_get_data_threshold(sd_journal *j, size_t *sz);
sd_journal_get_data()gets the data object associated with a specific field from the current journal entry. It takes four arguments: the journal context object, a string with the field name to request, plus a pair of pointers to pointer/size variables where the data object and its size shall be stored in. The field name should be an entry field name. Well-known field names are listed insystemd.journal-fields(7), but any field can be specified. The returned data is in a read-only memory map and is only valid until the next invocation ofsd_journal_get_data(),sd_journal_enumerate_data(),sd_journal_enumerate_available_data(), or when the read pointer is altered. Note that the data returned will be prefixed with the field name and "=". Also note that, by default, data fields larger than 64K might get truncated to 64K. This threshold may be changed and turned off withsd_journal_set_data_threshold()(see below).sd_journal_enumerate_data()may be used to iterate through all fields of the current entry. On each invocation the data for the next field is returned. The order of these fields is not defined. The data returned is in the same format as withsd_journal_get_data()and also follows the same life-time semantics.sd_journal_enumerate_available_data()is similar tosd_journal_enumerate_data(), but silently skips any fields which may be valid, but are too large or not supported by current implementation.sd_journal_restart_data()resets the data enumeration index to the beginning of the entry. The next invocation ofsd_journal_enumerate_data()will return the first field of the entry again. Note that theSD_JOURNAL_FOREACH_DATA()macro may be used as a handy wrapper aroundsd_journal_restart_data()andsd_journal_enumerate_available_data(). Note that these functions will not work beforesd_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_set_data_threshold()may be used to change the data field size threshold for data returned bysd_journal_get_data(),sd_journal_enumerate_data()andsd_journal_enumerate_unique(). This threshold is a hint only: it indicates that the client program is interested only in the initial parts of the data fields, up to the threshold in size — but the library might still return larger data objects. That means applications should not rely exclusively on this setting to limit the size of the data fields returned, but need to apply an explicit size limit on the returned data as well. This threshold defaults to 64K by default. To retrieve the complete data fields this threshold should be turned off by setting it to 0, so that the library always returns the complete data objects. It is recommended to set this threshold as low as possible since this relieves the library from having to decompress large compressed data objects in full.sd_journal_get_data_threshold()returns the currently configured data field size threshold.
sd_journal_get_data()returns 0 on success or a negative errno-style error code.sd_journal_enumerate_data()andsd_journal_enumerate_available_data()return a positive integer if the next field has been read, 0 when no more fields remain, or a negative errno-style error code.sd_journal_restart_data()does not return anything.sd_journal_set_data_threshold()andsd_journal_get_threshold()return 0 on success or a negative errno-style error code.Errors Returned errors may indicate the following problems:-EINVAL One of the required parameters isNULLor invalid. Added in version 246.-ECHILD The journal object was created in a different process, library or module instance. Added in version 246.-EADDRNOTAVAIL The read pointer is not positioned at a valid entry;sd_journal_next(3) or a related call has not been called at least once. Added in version 246.-ENOENT The current entry does not include the specified field. Added in version 246.-ENOMEM Memory allocation failed. Added in version 246.-ENOBUFS A compressed entry is too large. Added in version 246.-E2BIG The data field is too large for this computer architecture (e.g. above 4 GB on a 32-bit architecture). Added in version 246.-EPROTONOSUPPORT The journal is compressed with an unsupported method or the journal uses an unsupported feature. Added in version 246.-EBADMSG The journal is corrupted (possibly just the entry being iterated over). Added in version 246.-EIO An I/O error was reported by the kernel. Added in version 246.
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 thelibsystemd pkg-config(1) file.
Seesd_journal_next(3) for a complete example how to usesd_journal_get_data(). Use theSD_JOURNAL_FOREACH_DATA()macro to iterate through all fields of the current journal entry: ... int print_fields(sd_journal *j) { const void *data; size_t length; SD_JOURNAL_FOREACH_DATA(j, data, length) printf("%.*s\n", (int) length, data); } ...sd_journal_get_data(),sd_journal_enumerate_data(),sd_journal_restart_data(), andSD_JOURNAL_FOREACH_DATA()were added in version 187.sd_journal_set_data_threshold()andsd_journal_get_data_threshold()were added in version 196.sd_journal_enumerate_available_data()was added in version 246.
systemd(1),systemd.journal-fields(7),sd-journal(3),sd_journal_open(3),sd_journal_next(3),sd_journal_get_realtime_usec(3),sd_journal_query_unique(3)
This page is part of thesystemd (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 isnot part of the original manual page), send a mail to man-pages@man7.orgsystemd 258~rc2SD_JOURNAL_GET_DATA(3)Pages that refer to this page:sd-journal(3), sd_journal_add_match(3), sd_journal_enumerate_fields(3), sd_journal_get_catalog(3), sd_journal_get_realtime_usec(3), sd_journal_get_seqnum(3), sd_journal_next(3), sd_journal_open(3), sd_journal_query_unique(3), sd_journal_seek_head(3), systemd.directives(7), systemd.index(7)
HTML rendering created 2025-09-06 byMichael Kerrisk, author ofThe Linux Programming Interface. For details of in-depthLinux/UNIX system programming training courses that I teach, lookhere. Hosting byjambit GmbH. | |