x SuSE Linux 13.1-RELEASE x
x SuSE Linux 13.1-RELEASEx
SD_JOURNAL_NEXT(3) sd_journal_next SD_JOURNAL_NEXT(3)
NAME
sd_journal_next, sd_journal_previous, sd_journal_step_one,
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_step_one(sd_journal *j, int advanced);
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_step_one() also moves the read pointer. If the current
location is the head of the journal, e.g. when this is called following
sd_journal_seek_head(), then this is equivalent to sd_journal_next(),
and the argument advanced will be ignored. Similarly, if the current
location is the tail of the journal, e.g. when this is called following
sd_journal_seek_tail(), then this is equivalent to
sd_journal_previous(), and advanced will be ignored. Otherwise, this is
equivalent to sd_journal_next() when advanced is non-zero, and
sd_journal_previous() when advanced is zero.
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 skip parameter must be less than or equal to 2147483647
(2^3^1-1).
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
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.
Functions described here are available as a shared library, which can
be compiled against and linked to with the libsystemd pkg-config(1)
file.
EXAMPLES
Iterating through the journal:
/* SPDX-License-Identifier: MIT-0 */
#include <errno.h>
#include <stdio.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) {
errno = -r;
fprintf(stderr, "Failed to open journal: %m\n");
return 1;
}
SD_JOURNAL_FOREACH(j) {
const char *d;
size_t l;
r = sd_journal_get_data(j, "MESSAGE", (const void **)&d, &l);
if (r < 0) {
errno = -r;
fprintf(stderr, "Failed to read message field: %m\n");
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 254 SD_JOURNAL_NEXT(3)
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