sd_journal_add_match(3) — Linux manual page


SD_JOURNAL_ADD_MATCH(3)     sd_journal_add_match     SD_JOURNAL_ADD_MATCH(3)

NAME         top

       sd_journal_add_match, sd_journal_add_disjunction,
       sd_journal_add_conjunction, sd_journal_flush_matches - Add or remove
       entry matches

SYNOPSIS         top

       #include <systemd/sd-journal.h>

       int sd_journal_add_match(sd_journal *j, const void *data,
                                size_t size);

       int sd_journal_add_disjunction(sd_journal *j);

       int sd_journal_add_conjunction(sd_journal *j);

       void sd_journal_flush_matches(sd_journal *j);

DESCRIPTION         top

       sd_journal_add_match() adds a match by which to filter the entries of
       the journal file. Matches applied with this call will filter what can
       be iterated through and read from the journal file via calls like
       sd_journal_next(3) and sd_journal_get_data(3). Parameter data must be
       of the form "FIELD=value", where the FIELD part is a short uppercase
       string consisting only of 0–9, A–Z and the underscore; it may not
       begin with two underscores or be the empty string. The value part may
       be anything, including binary. Parameter size specifies the number of
       bytes in data (i.e. the length of FIELD, plus one, plus the length of
       value). Parameter size may also be specified as 0, in which case data
       must be a NUL-terminated string, and the bytes before the terminating
       zero are used as the match.

       If a match is applied, only entries with this field set will be
       iterated. Multiple matches may be active at the same time: If they
       apply to different fields, only entries with both fields set like
       this will be iterated. If they apply to the same fields, only entries
       where the field takes one of the specified values will be iterated.
       Well known fields are documented in systemd.journal-fields(7).
       Whenever a new match is added the current entry position is reset,
       and sd_journal_next(3) (or a similar call) needs to be called before
       entries can be read again.

       sd_journal_add_disjunction() may be used to insert a disjunction
       (i.e. logical OR) in the match list. If this call is invoked, all
       previously added matches since the last invocation of
       sd_journal_add_disjunction() or sd_journal_add_conjunction() are
       combined in an OR with all matches added afterwards, until
       sd_journal_add_disjunction() or sd_journal_add_conjunction() is
       invoked again to begin the next OR or AND term.

       sd_journal_add_conjunction() may be used to insert a conjunction
       (i.e. logical AND) in the match list. If this call is invoked, all
       previously added matches since the last invocation of
       sd_journal_add_conjunction() are combined in an AND with all matches
       added afterwards, until sd_journal_add_conjunction() is invoked again
       to begin the next AND term. The combination of
       sd_journal_add_match(), sd_journal_add_disjunction() and
       sd_journal_add_conjunction() may be used to build complex search
       terms, even though full logical expressions are not available. Note
       that sd_journal_add_conjunction() operates one level 'higher' than
       sd_journal_add_disjunction(). It is hence possible to build an
       expression of AND terms, consisting of OR terms, consisting of AND
       terms, consisting of OR terms of matches (the latter OR expression is
       implicitly created for matches with the same field name, see above).

       sd_journal_flush_matches() may be used to flush all matches,
       disjunction and conjunction terms again. After this call all
       filtering is removed and all entries in the journal will be iterated

       Note that filtering via matches only applies to the way the journal
       is read, it has no effect on storage on disk.

RETURN VALUE         top

       sd_journal_add_match(), sd_journal_add_disjunction() and
       sd_journal_add_conjunction() return 0 on success or a negative
       errno-style error code.  sd_journal_flush_matches() returns nothing.

NOTES         top

       These APIs are implemented as a shared library, which can be compiled
       and linked to with the libsystemd pkg-config(1) file.

EXAMPLES         top

       The following example adds matches to a journal context object to
       iterate only through messages generated by the Avahi service at the
       four error log levels, plus all messages of the message ID
       03bb1dab98ab4ecfbf6fff2738bdd964 coming from any service (this
       example lacks the necessary error checking):

           int add_matches(sd_journal *j) {
             sd_journal_add_match(j, "_SYSTEMD_UNIT=avahi-daemon.service", 0);
             sd_journal_add_match(j, "PRIORITY=0", 0);
             sd_journal_add_match(j, "PRIORITY=1", 0);
             sd_journal_add_match(j, "PRIORITY=2", 0);
             sd_journal_add_match(j, "PRIORITY=3", 0);
             sd_journal_add_match(j, "MESSAGE_ID=03bb1dab98ab4ecfbf6fff2738bdd964", 0);

SEE ALSO         top

       systemd(1), sd-journal(3), sd_journal_open(3), sd_journal_next(3),
       sd_journal_get_data(3), systemd.journal-fields(7)

COLOPHON         top

       This page is part of the systemd (systemd system and service manager)
       project.  Information about the project can be found at 
       ⟨⟩.  If you have a bug
       report for this manual page, see
       ⟨⟩.  This
       page was obtained from the project's upstream Git repository
       ⟨⟩ on 2020-11-01.  (At that
       time, the date of the most recent commit that was found in the repos‐
       itory was 2020-11-01.)  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 im‐
       provements to the information in this COLOPHON (which is not part of
       the original manual page), send a mail to

systemd 247                                          SD_JOURNAL_ADD_MATCH(3)

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