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_enumerate_available_unique, sd_journal_restart_unique,
8 SD_JOURNAL_FOREACH_UNIQUE - Read unique data 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_available_unique(sd_journal *j,
16 const void **data,
17 size_t *length);
18 int sd_journal_enumerate_unique(sd_journal *j, const void **data,
20 size_t *length);
21 void sd_journal_restart_unique(sd_journal *j);
23 SD_JOURNAL_FOREACH_UNIQUE(sd_journal *j, const void *data,
25 size_t length);
26
28 sd_journal_query_unique() queries the journal for all unique values the
29 specified field can take. It takes two arguments: the journal to query
30 and the field name to look for. Well-known field names are listed on
31 systemd.journal-fields(7), but any field can be specified. Field names
32 must be specified without a trailing "=". After this function has been
33 executed successfully the field values may be queried using
34 sd_journal_enumerate_unique() and
35 sd_journal_enumerate_available_unique(). Invoking one of those calls
36 will change the field name being queried and reset the enumeration
37 index to the first field value that matches.
38 sd_journal_enumerate_unique() may be used to iterate through all data
40 fields which match the previously selected field name as set with
41 sd_journal_query_unique(). On each invocation the next field data
42 matching the field name is returned. The order of the returned data
43 fields is not defined. It takes three arguments: the journal object,
44 plus a pair of pointers to pointer/size variables where the data object
45 and its size shall be stored. The returned data is in a read-only
46 memory map and is only valid until the next invocation of
47 sd_journal_enumerate_unique(). Note that the data returned will be
48 prefixed with the field name and "=". Note that this call is subject to
49 the data field size threshold as controlled by
50 sd_journal_set_data_threshold() and only the initial part of the field
51 up to the threshold is returned. An error is returned for fields which
52 cannot be retrieved. See the error list below for details.
53 sd_journal_enumerate_available_unique() is similar to
55 sd_journal_enumerate_unique(), but silently skips any fields which may
56 be valid, but are too large or not supported by current implementation.
57 sd_journal_restart_unique() resets the data enumeration index to the
59 beginning of the list. The next invocation of
60 sd_journal_enumerate_unique() will return the first field data matching
61 the field name again.
62 Note that the SD_JOURNAL_FOREACH_UNIQUE() macro may be used as a handy
64 wrapper around sd_journal_restart_unique() and
65 sd_journal_enumerate_available_unique().
66 Note that these functions currently are not influenced by matches set
68 with sd_journal_add_match() but this might change in a later version of
69 this software.
70 To enumerate all field names currently in use (and thus all suitable
72 field parameters for sd_journal_query_unique()), use the
73 sd_journal_enumerate_fields(3) call.
74
76 sd_journal_query_unique() returns 0 on success or a negative
77 errno-style error code. sd_journal_enumerate_unique() and
78 sd_journal_query_available_unique() return a positive integer if the
79 next field data has been read, 0 when no more fields remain, or a
80 negative errno-style error code. sd_journal_restart_unique() doesn't
81 return anything.
82 Errors
84 Returned errors may indicate the following problems:
85 -EINVAL
87 One of the required parameters is NULL or invalid.
88 -ECHILD
90 The journal object was created in a different process, library or
91 module instance.
92 -EADDRNOTAVAIL
94 The read pointer is not positioned at a valid entry;
95 sd_journal_next(3) or a related call has not been called at least
96 once.
97 -ENOENT
99 The current entry does not include the specified field.
100 -ENOBUFS
102 A compressed entry is too large.
103 -E2BIG
105 The data field is too large for this computer architecture (e.g.
106 above 4 GB on a 32-bit architecture).
107 -EPROTONOSUPPORT
109 The journal is compressed with an unsupported method or the journal
110 uses an unsupported feature.
111 -EBADMSG
113 The journal is corrupted (possibly just the entry being iterated
114 over).
115 -EIO
117 An I/O error was reported by the kernel.
118
120 All functions listed here are thread-agnostic and only a single
121 specific thread may operate on a given object during its entire
122 lifetime. It's safe to allocate multiple independent objects and use
123 each from a specific thread in parallel. However, it's not safe to
124 allocate such an object in one thread, and operate or free it from any
125 other, even if locking is used to ensure these threads don't operate on
126 it at the very same time.
127 Functions described here are available as a shared library, which can
129 be compiled against and linked to with the libsystemd pkg-config(1)
130 file.
131
133 Use the SD_JOURNAL_FOREACH_UNIQUE() macro to iterate through all values
134 a field of the journal can take (and which can be accessed on the given
135 architecture and are not compressed with an unsupported mechanism). The
136 following example lists all unit names referenced in the journal:
137 /* SPDX-License-Identifier: MIT-0 */
139 #include <errno.h>
141 #include <stdio.h>
142 #include <systemd/sd-journal.h>
143 int main(int argc, char *argv[]) {
145 sd_journal *j;
146 const void *d;
147 size_t l;
148 int r;
149 r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY);
151 if (r < 0) {
152 errno = -r;
153 fprintf(stderr, "Failed to open journal: %m\n");
154 return 1;
155 }
156 r = sd_journal_query_unique(j, "_SYSTEMD_UNIT");
157 if (r < 0) {
158 errno = -r;
159 fprintf(stderr, "Failed to query journal: %m\n");
160 return 1;
161 }
162 SD_JOURNAL_FOREACH_UNIQUE(j, d, l)
163 printf("%.*s\n", (int) l, (const char*) d);
164 sd_journal_close(j);
165 return 0;
166 }
167
169 systemd(1), systemd.journal-fields(7), sd-journal(3),
170 sd_journal_open(3), sd_journal_enumerate_fields(3),
171 sd_journal_get_data(3), sd_journal_add_match(3)
172systemd 254 SD_JOURNAL_QUERY_UNIQUE(3)