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NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | EXAMPLES | HISTORY | SEE ALSO | COLOPHON |
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SD_JOURNAL_ADD_MATCH(3) sd_journal_add_match SD_JOURNAL_ADD_MATCH(3)
sd_journal_add_match, sd_journal_add_disjunction,
sd_journal_add_conjunction, sd_journal_flush_matches - Add or
remove entry matches
#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);
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.
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.
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.
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);
}
sd_journal_add_match(), sd_journal_add_disjunction(), and
sd_journal_flush_matches() were added in version 187.
sd_journal_add_conjunction() was added in version 202.
systemd(1), sd-journal(3), sd_journal_open(3),
sd_journal_next(3), sd_journal_get_data(3),
systemd.journal-fields(7)
This page is part of the systemd (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 2024-06-14. (At that
time, the date of the most recent commit that was found in the
repository was 2024-06-13.) 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 is not part of the original manual page), send a mail to
[email protected]
systemd 257~devel SD_JOURNAL_ADD_MATCH(3)
Pages that refer to this page: sd-journal(3), sd_journal_enumerate_fields(3), sd_journal_query_unique(3), systemd.directives(7), systemd.index(7), systemd.journal-fields(7)
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HTML rendering created 2024-06-26 by Michael Kerrisk, author of The Linux Programming Interface. For details of in-depth Linux/UNIX system programming training courses that I teach, look here. Hosting by jambit GmbH. |
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