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NAME |SYNOPSIS |DESCRIPTION |RETURN VALUE |NOTES |EXAMPLES |HISTORY |SEE ALSO |COLOPHON | |
SD_JOURN...RY_UNIQUE(3) sd_journal_query_uniqueSD_JOURN...RY_UNIQUE(3)sd_journal_query_unique, sd_journal_enumerate_unique, sd_journal_enumerate_available_unique, sd_journal_restart_unique, SD_JOURNAL_FOREACH_UNIQUE - Read unique data fields from the journal
#include <systemd/sd-journal.h>int sd_journal_query_unique(sd_journal *j, const char *field);int sd_journal_enumerate_available_unique(sd_journal *j,const void **data,size_t *length);int sd_journal_enumerate_unique(sd_journal *j, const void **data,size_t *length);void sd_journal_restart_unique(sd_journal *j);SD_JOURNAL_FOREACH_UNIQUE(sd_journal *j, const void *data,size_tlength);
sd_journal_query_unique()queries the journal for all unique values the specified field can take. It takes two arguments: the journal to query and the field name to look for. Well-known field names are listed onsystemd.journal-fields(7), but any field can be specified. Field names must be specified without a trailing "=". After this function has been executed successfully the field values may be queried usingsd_journal_enumerate_unique()andsd_journal_enumerate_available_unique(). Invoking one of those calls will change the field name being queried and reset the enumeration index to the first field value that matches.sd_journal_enumerate_unique()may be used to iterate through all data fields which match the previously selected field name as set withsd_journal_query_unique(). On each invocation the next field data matching the field name is returned. The order of the returned data fields is not defined. It takes three arguments: the journal object, plus a pair of pointers to pointer/size variables where the data object and its size shall be stored. The returned data is in a read-only memory map and is only valid until the next invocation ofsd_journal_enumerate_unique(). Note that the data returned will be prefixed with the field name and "=". Note that this call is subject to the data field size threshold as controlled bysd_journal_set_data_threshold()and only the initial part of the field up to the threshold is returned. An error is returned for fields which cannot be retrieved. See the error list below for details.sd_journal_enumerate_available_unique()is similar tosd_journal_enumerate_unique(), but silently skips any fields which may be valid, but are too large or not supported by current implementation.sd_journal_restart_unique()resets the data enumeration index to the beginning of the list. The next invocation ofsd_journal_enumerate_unique()will return the first field data matching the field name again. Note that theSD_JOURNAL_FOREACH_UNIQUE()macro may be used as a handy wrapper aroundsd_journal_restart_unique()andsd_journal_enumerate_available_unique(). Note that these functions currently are not influenced by matches set withsd_journal_add_match()but this might change in a later version of this software. To enumerate all field names currently in use (and thus all suitable field parameters forsd_journal_query_unique()), use thesd_journal_enumerate_fields(3) call.
sd_journal_query_unique()returns 0 on success or a negative errno-style error code.sd_journal_enumerate_unique()andsd_journal_query_available_unique()return a positive integer if the next field data has been read, 0 when no more fields remain, or a negative errno-style error code.sd_journal_restart_unique() does not return anything.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.-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.
Use theSD_JOURNAL_FOREACH_UNIQUE()macro to iterate through all values a field of the journal can take (and which can be accessed on the given architecture and are not compressed with an unsupported mechanism). The following example lists all unit names referenced in the journal: /* SPDX-License-Identifier: MIT-0 */ #include <errno.h> #include <stdio.h> #include <systemd/sd-journal.h> int main(int argc, char *argv[]) { sd_journal *j; const void *d; size_t l; int r; r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY); if (r < 0) { fprintf(stderr, "Failed to open journal: %s\n", strerror(-r)); return 1; } r = sd_journal_query_unique(j, "_SYSTEMD_UNIT"); if (r < 0) { fprintf(stderr, "Failed to query journal: %s\n", strerror(-r)); return 1; } SD_JOURNAL_FOREACH_UNIQUE(j, d, l) printf("%.*s\n", (int) l, (const char*) d); sd_journal_close(j); return 0; }sd_journal_query_unique(),sd_journal_enumerate_unique(),sd_journal_restart_unique(), andSD_JOURNAL_FOREACH_UNIQUE()were added in version 195.sd_journal_enumerate_available_unique()was added in version 246.
systemd(1),systemd.journal-fields(7),sd-journal(3),sd_journal_open(3),sd_journal_enumerate_fields(3),sd_journal_get_data(3),sd_journal_add_match(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_JOURN...RY_UNIQUE(3)Pages that refer to this page:sd-journal(3), sd_journal_enumerate_fields(3), sd_journal_get_data(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. | |