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SD_JOURNAL_NEXT(3) sd_journal_next SD_JOURNAL_NEXT(3)
NAME
sd_journal_next, sd_journal_previous, sd_journal_next_skip, sd_journal_previous_skip,
SD_JOURNAL_FOREACH, SD_JOURNAL_FOREACH_BACKWARDS - Advance or set back the read pointer in
the journal
SYNOPSIS
#include <systemd/sd-journal.h>
int sd_journal_next(sd_journal* j);
int sd_journal_previous(sd_journal* j);
int sd_journal_next_skip(sd_journal* j, uint64_t skip);
int sd_journal_previous_skip(sd_journal* j, uint64_t skip);
SD_JOURNAL_FOREACH(sd_journal* j);
SD_JOURNAL_FOREACH_BACKWARDS(sd_journal* j);
DESCRIPTION
sd_journal_next() advances the read pointer into the journal by one entry. The only
argument taken is a journal context object as allocated via sd_journal_open(3). After
successful invocation the entry may be read with functions such as sd_journal_get_data(3).
Similarly, sd_journal_previous() sets the read pointer back one entry.
sd_journal_next_skip() and sd_journal_previous_skip() advance/set back the read pointer by
multiple entries at once, as specified in the skip parameter.
The journal is strictly ordered by reception time, and hence advancing to the next entry
guarantees that the entry then pointing to is later in time than then previous one, or has
the same timestamp.
Note that sd_journal_get_data(3) and related calls will fail unless sd_journal_next() has
been invoked at least once in order to position the read pointer on a journal entry.
Note that the SD_JOURNAL_FOREACH() macro may be used as a wrapper around
sd_journal_seek_head(3) and sd_journal_next() in order to make iterating through the
journal easier. See below for an example. Similarly, SD_JOURNAL_FOREACH_BACKWARDS() may be
used for iterating the journal in reverse order.
RETURN VALUE
The four calls return the number of entries advanced/set back on success or a negative
errno-style error code. When the end or beginning of the journal is reached, a number
smaller than requested is returned. More specifically, if sd_journal_next() or
sd_journal_previous() reach the end/beginning of the journal they will return 0, instead
of 1 when they are successful. This should be considered an EOF marker.
NOTES
The sd_journal_next(), sd_journal_previous(), sd_journal_next_skip() and
sd_journal_previous_skip() interfaces are available as a shared library, which can be
compiled and linked to with the libsystemd-journal pkg-config(1) file.
EXAMPLES
Iterating through the journal:
#include <stdio.h>
#include <string.h>
#include <systemd/sd-journal.h>
int main(int argc, char *argv[]) {
int r;
sd_journal *j;
r = sd_journal_open(&j, SD_JOURNAL_LOCAL_ONLY);
if (r < 0) {
fprintf(stderr, "Failed to open journal: %s\n", strerror(-r));
return 1;
}
SD_JOURNAL_FOREACH(j) {
const char *d;
size_t l;
r = sd_journal_get_data(j, "MESSAGE", &d, &l);
if (r < 0) {
fprintf(stderr, "Failed to read message field: %s\n", strerror(-r));
continue;
}
printf("%.*s\n", (int) l, d);
}
sd_journal_close(j);
return 0;
}
SEE ALSO
systemd(1), sd-journal(3), sd_journal_open(3), sd_journal_get_data(3),
sd_journal_get_realtime_usec(3), sd_journal_get_cursor(3)
systemd 208 SD_JOURNAL_NEXT(3) |
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