sd_journal_query_unique(3)

1SD_JOURNAL_QUERY_UNIQUE(3)  sd_journal_query_unique SD_JOURNAL_QUERY_UNIQUE(3)
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NAME

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

SYNOPSIS

11       #include <systemd/sd-journal.h>
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13       int sd_journal_query_unique(sd_journal *j, const char *field);
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15       int sd_journal_enumerate_unique(sd_journal *j, const void **data,
16                                       size_t *length);
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18       void sd_journal_restart_unique(sd_journal *j);
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20       SD_JOURNAL_FOREACH_UNIQUE(sd_journal *j, const void *data,
21                                 size_t length);
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DESCRIPTION

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.
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34       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().
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47       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.
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52       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().
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56       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.
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60       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.
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RETURN VALUE

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.
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NOTES

72       All functions listed here are thread-agnostic and only a single thread
73       may operate on a given sd_journal object.
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75       These APIs are implemented as a shared library, which can be compiled
76       and linked to with the libsystemd pkg-config(1) file.
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EXAMPLES

79       Use the SD_JOURNAL_FOREACH_UNIQUE macro to iterate through all values a
80       field of the journal can take. The following example lists all unit
81       names referenced in the journal:
82
83           #include <stdio.h>
84           #include <string.h>
85           #include <systemd/sd-journal.h>
86
87           int main(int argc, char *argv[]) {
88                   sd_journal *j;
89                   const void *d;
90                   size_t l;
91                   int r;
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93                   r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY);
94                   if (r < 0) {
95                           fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
96                           return 1;
97                   }
98                   r = sd_journal_query_unique(j, "_SYSTEMD_UNIT");
99                   if (r < 0) {
100                           fprintf(stderr, "Failed to query journal: %s\n", strerror(-r));
101                           return 1;
102                   }
103                   SD_JOURNAL_FOREACH_UNIQUE(j, d, l)
104                           printf("%.*s\n", (int) l, (const char*) d);
105                   sd_journal_close(j);
106                   return 0;
107           }
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NAME

SYNOPSIS

DESCRIPTION

RETURN VALUE

NOTES

EXAMPLES

SEE ALSO