1SD_JOURNAL_QUERY_UNIQUE(3) sd_journal_query_unique SD_JOURNAL_QUERY_UNIQUE(3)
2
6 sd_journal_query_unique, sd_journal_enumerate_unique,
7 sd_journal_restart_unique, SD_JOURNAL_FOREACH_UNIQUE - Read unique data
8 fields from the journal
9
11 #include <systemd/sd-journal.h>
12 int sd_journal_query_unique(sd_journal *j, const char *field);
14 int sd_journal_enumerate_unique(sd_journal *j, const void **data,
16 size_t *length);
17 void sd_journal_restart_unique(sd_journal *j);
19 SD_JOURNAL_FOREACH_UNIQUE(sd_journal *j, const void *data,
21 size_t length);
22
24 sd_journal_query_unique() queries the journal for all unique values the
25 specified field can take. It takes two arguments: the journal to query
26 and the field name to look for. Well-known field names are listed on
27 systemd.journal-fields(7). Field names must be specified without a
28 trailing '='. After this function has been executed successfully the
29 field values may be queried using sd_journal_enumerate_unique().
30 Invoking this call a second time will change the field name being
31 queried and reset the enumeration index to the first field value that
32 matches.
33 sd_journal_enumerate_unique() may be used to iterate through all data
35 fields which match the previously selected field name as set with
36 sd_journal_query_unique(). On each invocation the next field data
37 matching the field name is returned. The order of the returned data
38 fields is not defined. It takes three arguments: the journal context
39 object, plus a pair of pointers to pointer/size variables where the
40 data object and its size shall be stored in. The returned data is in a
41 read-only memory map and is only valid until the next invocation of
42 sd_journal_enumerate_unique(). Note that the data returned will be
43 prefixed with the field name and '='. Note that this call is subject to
44 the data field size threshold as controlled by
45 sd_journal_set_data_threshold().
46 sd_journal_restart_unique() resets the data enumeration index to the
48 beginning of the list. The next invocation of
49 sd_journal_enumerate_unique() will return the first field data matching
50 the field name again.
51 Note that the SD_JOURNAL_FOREACH_UNIQUE() macro may be used as a handy
53 wrapper around sd_journal_restart_unique() and
54 sd_journal_enumerate_unique().
55 Note that these functions currently are not influenced by matches set
57 with sd_journal_add_match() but this might change in a later version of
58 this software.
59 To enumerate all field names currently in use (and thus all suitable
61 field parameters for sd_journal_query_unique()), use the
62 sd_journal_enumerate_fields(3) call.
63
65 sd_journal_query_unique() returns 0 on success or a negative
66 errno-style error code. sd_journal_enumerate_unique() returns a
67 positive integer if the next field data has been read, 0 when no more
68 fields are known, or a negative errno-style error code.
69 sd_journal_restart_unique() returns nothing.
70
72 All functions listed here are thread-agnostic and only a single
73 specific thread may operate on a given object during its entire
74 lifetime. It's safe to allocate multiple independent objects and use
75 each from a specific thread in parallel. However, it's not safe to
76 allocate such an object in one thread, and operate or free it from any
77 other, even if locking is used to ensure these threads don't operate on
78 it at the very same time.
79 These APIs are implemented as a shared library, which can be compiled
81 and linked to with the libsystemd pkg-config(1) file.
82
84 Use the SD_JOURNAL_FOREACH_UNIQUE macro to iterate through all values a
85 field of the journal can take. The following example lists all unit
86 names referenced in the journal:
87 #include <stdio.h>
89 #include <string.h>
90 #include <systemd/sd-journal.h>
91 int main(int argc, char *argv[]) {
93 sd_journal *j;
94 const void *d;
95 size_t l;
96 int r;
97 r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY);
99 if (r < 0) {
100 fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
101 return 1;
102 }
103 r = sd_journal_query_unique(j, "_SYSTEMD_UNIT");
104 if (r < 0) {
105 fprintf(stderr, "Failed to query journal: %s\n", strerror(-r));
106 return 1;
107 }
108 SD_JOURNAL_FOREACH_UNIQUE(j, d, l)
109 printf("%.*s\n", (int) l, (const char*) d);
110 sd_journal_close(j);
111 return 0;
112 }
113
115 systemd(1), systemd.journal-fields(7), sd-journal(3),
116 sd_journal_open(3), sd_journal_enumerate_fields(3),
117 sd_journal_get_data(3), sd_journal_add_match(3)
118systemd 243 SD_JOURNAL_QUERY_UNIQUE(3)