|
NAME | SYNOPSIS | DESCRIPTION | RETURN VALUE | NOTES | EXAMPLES | SEE ALSO | COLOPHON |
SD_JOURNAL_QUERY_UNIQUE(3) sd_journal_query_uniqueSD_JOURNAL_QUERY_UNIQUE(3)
sd_journal_query_unique, sd_journal_enumerate_unique,
sd_journal_enumerate_available_unique, sd_journal_restart_unique,
SD_JOURNAL_FOREACH_UNIQUE - Read unique data fields from the journal
#include <systemd/sd-journal.h>
int sd_journal_query_unique(sd_journal *j, const char *field);
int sd_journal_enumerate_available_unique(sd_journal *j,
const void **data,
size_t *length);
int sd_journal_enumerate_unique(sd_journal *j, const void **data,
size_t *length);
void sd_journal_restart_unique(sd_journal *j);
SD_JOURNAL_FOREACH_UNIQUE(sd_journal *j, const void *data,
size_t length);
sd_journal_query_unique() queries the journal for all unique values
the specified field can take. It takes two arguments: the journal to
query and the field name to look for. Well-known field names are
listed on systemd.journal-fields(7), but any field can be specified.
Field names must be specified without a trailing "=". After this
function has been executed successfully the field values may be
queried using sd_journal_enumerate_unique() and
sd_journal_enumerate_available_unique(). Invoking one of those calls
will change the field name being queried and reset the enumeration
index to the first field value that matches.
sd_journal_enumerate_unique() may be used to iterate through all data
fields which match the previously selected field name as set with
sd_journal_query_unique(). On each invocation the next field data
matching the field name is returned. The order of the returned data
fields is not defined. It takes three arguments: the journal object,
plus a pair of pointers to pointer/size variables where the data
object and its size shall be stored. The returned data is in a
read-only memory map and is only valid until the next invocation of
sd_journal_enumerate_unique(). Note that the data returned will be
prefixed with the field name and "=". Note that this call is subject
to the data field size threshold as controlled by
sd_journal_set_data_threshold() and only the initial part of the
field up to the threshold is returned. An error is returned for
fields which cannot be retrieved. See the error list below for
details.
sd_journal_enumerate_available_unique() is similar to
sd_journal_enumerate_unique(), but silently skips any fields which
may be valid, but are too large or not supported by current
implementation.
sd_journal_restart_unique() resets the data enumeration index to the
beginning of the list. The next invocation of
sd_journal_enumerate_unique() will return the first field data
matching the field name again.
Note that the SD_JOURNAL_FOREACH_UNIQUE() macro may be used as a
handy wrapper around sd_journal_restart_unique() and
sd_journal_enumerate_available_unique().
Note that these functions currently are not influenced by matches set
with sd_journal_add_match() but this might change in a later version
of this software.
To enumerate all field names currently in use (and thus all suitable
field parameters for sd_journal_query_unique()), use the
sd_journal_enumerate_fields(3) call.
sd_journal_query_unique() returns 0 on success or a negative
errno-style error code. sd_journal_enumerate_unique() and and
sd_journal_query_available_unique() return a positive integer if the
next field data has been read, 0 when no more fields remain, or a
negative errno-style error code. sd_journal_restart_unique() doesn't
return anything.
Errors
Returned errors may indicate the following problems:
-EINVAL
One of the required parameters is NULL or invalid.
-ECHILD
The journal object was created in a different process.
-EADDRNOTAVAIL
The read pointer is not positioned at a valid entry;
sd_journal_next(3) or a related call has not been called at least
once.
-ENOENT
The current entry does not include the specified field.
-ENOBUFS
A compressed entry is too large.
-E2BIG
The data field is too large for this computer architecture (e.g.
above 4 GB on a 32-bit architecture).
-EPROTONOSUPPORT
The journal is compressed with an unsupported method or the
journal uses an unsupported feature.
-EBADMSG
The journal is corrupted (possibly just the entry being iterated
over).
-EIO
An I/O error was reported by the kernel.
All functions listed here are thread-agnostic and only a single
specific thread may operate on a given object during its entire
lifetime. It's safe to allocate multiple independent objects and use
each from a specific thread in parallel. However, it's not safe to
allocate such an object in one thread, and operate or free it from
any other, even if locking is used to ensure these threads don't
operate on it at the very same time.
These APIs are implemented as a shared library, which can be compiled
and linked to with the libsystemd pkg-config(1) file.
Use the SD_JOURNAL_FOREACH_UNIQUE macro to iterate through all values
a field of the journal can take (and which can be accessed on the
given architecture and are not compressed with an unsupported
mechanism). The following example lists all unit names referenced in
the journal:
#include <stdio.h>
#include <string.h>
#include <systemd/sd-journal.h>
int main(int argc, char *argv[]) {
sd_journal *j;
const void *d;
size_t l;
int r;
r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY);
if (r < 0) {
fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
return 1;
}
r = sd_journal_query_unique(j, "_SYSTEMD_UNIT");
if (r < 0) {
fprintf(stderr, "Failed to query journal: %s\n", strerror(-r));
return 1;
}
SD_JOURNAL_FOREACH_UNIQUE(j, d, l)
printf("%.*s\n", (int) l, (const char*) d);
sd_journal_close(j);
return 0;
}
systemd(1), systemd.journal-fields(7), sd-journal(3),
sd_journal_open(3), sd_journal_enumerate_fields(3),
sd_journal_get_data(3), sd_journal_add_match(3)
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 2020-08-13. (At that
time, the date of the most recent commit that was found in the repos‐
itory was 2020-08-11.) 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 man-pages@man7.org
systemd 246 SD_JOURNAL_QUERY_UNIQUE(3)