1SD_JOURNAL_ADD_MATCH(3) sd_journal_add_match SD_JOURNAL_ADD_MATCH(3)
2
3
4
6 sd_journal_add_match, sd_journal_add_disjunction,
7 sd_journal_add_conjunction, sd_journal_flush_matches - Add or remove
8 entry matches
9
11 #include <systemd/sd-journal.h>
12
13 int sd_journal_add_match(sd_journal *j, const void *data, size_t size);
14
15 int sd_journal_add_disjunction(sd_journal *j);
16
17 int sd_journal_add_conjunction(sd_journal *j);
18
19 void sd_journal_flush_matches(sd_journal *j);
20
22 sd_journal_add_match() adds a match by which to filter the entries of
23 the journal file. Matches applied with this call will filter what can
24 be iterated through and read from the journal file via calls like
25 sd_journal_next(3) and sd_journal_get_data(3). Parameter data must be
26 of the form "FIELD=value", where the FIELD part is a short uppercase
27 string consisting only of 0–9, A–Z and the underscore; it may not begin
28 with two underscores or be the empty string. The value part may be
29 anything, including binary. Parameter size specifies the number of
30 bytes in data (i.e. the length of FIELD, plus one, plus the length of
31 value). Parameter size may also be specified as 0, in which case data
32 must be a NUL-terminated string, and the bytes before the terminating
33 zero are used as the match.
34
35 If a match is applied, only entries with this field set will be
36 iterated. Multiple matches may be active at the same time: If they
37 apply to different fields, only entries with both fields set like this
38 will be iterated. If they apply to the same fields, only entries where
39 the field takes one of the specified values will be iterated. Well
40 known fields are documented in systemd.journal-fields(7). Whenever a
41 new match is added the current entry position is reset, and
42 sd_journal_next(3) (or a similar call) needs to be called before
43 entries can be read again.
44
45 sd_journal_add_disjunction() may be used to insert a disjunction (i.e.
46 logical OR) in the match list. If this call is invoked, all previously
47 added matches since the last invocation of sd_journal_add_disjunction()
48 or sd_journal_add_conjunction() are combined in an OR with all matches
49 added afterwards, until sd_journal_add_disjunction() or
50 sd_journal_add_conjunction() is invoked again to begin the next OR or
51 AND term.
52
53 sd_journal_add_conjunction() may be used to insert a conjunction (i.e.
54 logical AND) in the match list. If this call is invoked, all previously
55 added matches since the last invocation of sd_journal_add_conjunction()
56 are combined in an AND with all matches added afterwards, until
57 sd_journal_add_conjunction() is invoked again to begin the next AND
58 term. The combination of sd_journal_add_match(),
59 sd_journal_add_disjunction() and sd_journal_add_conjunction() may be
60 used to build complex search terms, even though full logical
61 expressions are not available. Note that sd_journal_add_conjunction()
62 operates one level 'higher' than sd_journal_add_disjunction(). It is
63 hence possible to build an expression of AND terms, consisting of OR
64 terms, consisting of AND terms, consisting of OR terms of matches (the
65 latter OR expression is implicitly created for matches with the same
66 field name, see above).
67
68 sd_journal_flush_matches() may be used to flush all matches,
69 disjunction and conjunction terms again. After this call all filtering
70 is removed and all entries in the journal will be iterated again.
71
72 Note that filtering via matches only applies to the way the journal is
73 read, it has no effect on storage on disk.
74
76 sd_journal_add_match(), sd_journal_add_disjunction() and
77 sd_journal_add_conjunction() return 0 on success or a negative
78 errno-style error code. sd_journal_flush_matches() returns nothing.
79
81 These APIs are implemented as a shared library, which can be compiled
82 and linked to with the libsystemd pkg-config(1) file.
83
85 The following example adds matches to a journal context object to
86 iterate only through messages generated by the Avahi service at the
87 four error log levels, plus all messages of the message ID
88 03bb1dab98ab4ecfbf6fff2738bdd964 coming from any service (this example
89 lacks the necessary error checking):
90
91 ...
92 int add_matches(sd_journal *j) {
93 sd_journal_add_match(j, "_SYSTEMD_UNIT=avahi-daemon.service", 0);
94 sd_journal_add_match(j, "PRIORITY=0", 0);
95 sd_journal_add_match(j, "PRIORITY=1", 0);
96 sd_journal_add_match(j, "PRIORITY=2", 0);
97 sd_journal_add_match(j, "PRIORITY=3", 0);
98 sd_journal_add_disjunction(j);
99 sd_journal_add_match(j, "MESSAGE_ID=03bb1dab98ab4ecfbf6fff2738bdd964", 0);
100 }
101
103 systemd(1), sd-journal(3), sd_journal_open(3), sd_journal_next(3),
104 sd_journal_get_data(3), systemd.journal-fields(7)
105
106
107
108systemd 251 SD_JOURNAL_ADD_MATCH(3)