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sd-journal(3) [centos man page]

SD-JOURNAL(3)							    sd-journal							     SD-JOURNAL(3)

sd-journal - APIs for submitting and querying log entries to and from the journal SYNOPSIS
#include <systemd/sd-journal.h> pkg-config --cflags --libs libsystemd-journal DESCRIPTION
sd-journal.h provides APIs to submit and query log entries. The APIs exposed act both as client for the systemd-journald.service(8) journal service and as parser for the journal files on disk. See sd_journal_print(3), sd_journal_stream_fd(3), sd_journal_open(3), sd_journal_next(3), sd_journal_get_realtime_usec(3), sd_journal_add_match(3), sd_journal_seek_head(3), sd_journal_get_cursor(3), sd_journal_cutoff_realtime_usec(3), sd_journal_get_usage(3), sd_journal_get_catalog(3) and sd_journal_get_fd(3) for more information about the functions implemented. Command line access for submitting entries to the journal is available with the systemd-cat(1) tool. Command line access for querying entries from the journal is available with the journalctl(1) tool. NOTES
These APIs are implemented 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_print(3), sd_journal_stream_fd(3), sd_journal_open(3), sd_journal_next(3), sd_journal_get_data(3), sd_journal_get_realtime_usec(3), sd_journal_add_match(3), sd_journal_seek_head(3), sd_journal_get_cursor(3), sd_journal_cutoff_realtime_usec(3), sd_journal_get_usage(3), sd_journal_get_fd(3), sd_journal_query_unique(3), sd_journal_get_catalog(3), journalctl(1), sd-id128(3), pkg-config(1) systemd 208 SD-JOURNAL(3)

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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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