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sd_journal_next(3) [centos man page]

SD_JOURNAL_NEXT(3)						  sd_journal_next						SD_JOURNAL_NEXT(3)

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 ", 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 ", strerror(-r)); continue; } printf("%.*s ", (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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SD_JOURNAL_SEEK_HEAD(3) 				       sd_journal_seek_head					   SD_JOURNAL_SEEK_HEAD(3)

sd_journal_seek_head, sd_journal_seek_tail, sd_journal_seek_monotonic_usec, sd_journal_seek_realtime_usec, sd_journal_seek_cursor - Seek to a position in the journal SYNOPSIS
#include <systemd/sd-journal.h> int sd_journal_seek_head(sd_journal* j); int sd_journal_seek_tail(sd_journal* j); int sd_journal_seek_monotonic_usec(sd_journal* j, sd_id128_t boot_id, uint64_t usec); int sd_journal_seek_realtime_usec(sd_journal* j, uint64_t usec); int sd_journal_seek_cursor(sd_journal* j, const char * cursor); DESCRIPTION
sd_journal_seek_head() seeks to the beginning of the journal, i.e. the oldest available entry. Similarly, sd_journal_seek_tail() may be used to seek to the end of the journal, i.e. the most recent available entry. sd_journal_seek_monotonic_usec() seeks to the entry with the specified monotonic timestamp, i.e. CLOCK_MONOTONIC. Since monotonic time restarts on every reboot a boot ID needs to be specified as well. sd_journal_seek_realtime_usec() seeks to the entry with the specified realtime (wallclock) timestamp, i.e. CLOCK_REALTIME. Note that the realtime clock is not necessarily monotonic. If a realtime timestamp is ambiguous, it is not defined which position is sought to. sd_journal_seek_cursor() seeks to the entry located at the specified cursor string. For details on cursors, see sd_journal_get_cursor(3). If no entry matching the specified cursor is found the call will seek to the next closest entry (in terms of time) instead. To verify whether the newly selected entry actually matches the cursor, use sd_journal_test_cursor(3). Note that these calls do not actually make any entry the new current entry, this needs to be done in a separate step with a subsequent sd_journal_next(3) invocation (or a similar call). Only then, entry data may be retrieved via sd_journal_get_data(3). If no entry exists that matches exactly the specified seek address, the next closest is sought to. If sd_journal_next(3) is used, the closest following entry will be sought to, if sd_journal_previous(3) is used the closest preceding entry is sought to. RETURN VALUE
The functions return 0 on success or a negative errno-style error code. NOTES
The sd_journal_seek_head(), sd_journal_seek_tail(), sd_journal_seek_monotonic_usec(), sd_journal_seek_realtime_usec(), and sd_journal_seek_cursor() interfaces are available as a shared library, which can be compiled and linked to with the libsystemd-journal pkg- config(1) file. SEE ALSO
systemd(1), sd-journal(3), sd_journal_open(3), sd_journal_next(3), sd_journal_get_data(3), sd_journal_get_cursor(3), sd_journal_get_realtime_usec(3) systemd 208 SD_JOURNAL_SEEK_HEAD(3)
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