x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
SD_JOURNAL_ADD_MATCH(3) sd_journal_add_match SD_JOURNAL_ADD_MATCH(3)
NAME
sd_journal_add_match, sd_journal_add_disjunction,
sd_journal_add_conjunction, sd_journal_flush_matches - Add or remove
entry matches
SYNOPSIS
#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
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 again.
Note that filtering via matches only applies to the way the journal is
read, it has no effect on storage on disk.
RETURN VALUE
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
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.
EXAMPLES
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_disjunction(j);
sd_journal_add_match(j, "MESSAGE_ID=03bb1dab98ab4ecfbf6fff2738bdd964", 0);
}
SEE ALSO
systemd(1), sd-journal(3), sd_journal_open(3), sd_journal_next(3),
sd_journal_get_data(3), systemd.journal-fields(7)
systemd 254 SD_JOURNAL_ADD_MATCH(3)
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