sd_journal_get_realtime_usec, sd_journal_get_monotonic_usec — Read timestamps from the current journal entry
#include <systemd/sd-journal.h>
| int sd_journal_get_realtime_usec( | sd_journal* j, | 
| uint64_t* usec ); | 
| int sd_journal_get_monotonic_usec( | sd_journal* j, | 
| uint64_t* usec, | |
| sd_id128_t* boot_id ); | 
sd_journal_get_realtime_usec()
                gets the realtime (wallclock) timestamp of the
                current journal entry.  It takes two arguments: the
                journal context object and a pointer to a 64 Bit
                unsigned integer to store the timestamp in. The
                timestamp is in microseconds since the epoch,
                i.e. CLOCK_REALTIME.
sd_journal_get_monotonic_usec()
                gets the monotonic timestamp of the current
                journal entry.  It takes three arguments: the journal
                context object, a pointer to a 64 Bit unsigned integer
                to store the timestamp in as well as a 128 Bit ID
                buffer to store the boot ID of the monotonic timestamp
                in. The timestamp is in microseconds since boot-up of
                the specific boot, i.e. CLOCK_MONOTONIC. Since the
                monotonic clock begins new with every reboot it only
                defines a well-defined point in time when used
                together with an identifier identifying the boot, see
                sd_id128_get_boot(3)
                for more information. If the boot ID parameter is
                passed NULL the function will fail if the monotonic
                timestamp of the current entry is not of the current
                system boot.
Note that these functions will not work before sd_journal_next(3) (or related call) has been called at least once, in order to position the read pointer at a valid entry.
sd_journal_get_realtime_usec()
                and
                sd_journal_get_monotonic_usec()
                returns 0 on success or a negative errno-style error
                code. If the boot ID parameter was passed NULL and the
                monotonic timestamp of the current journal entry is
                not of the current system boot, -ESTALE is returned by sd_journal_get_monotonic_usec().
The
                sd_journal_get_realtime_usec()
                and
                sd_journal_get_monotonic_usec()
                interfaces are available as shared library, which can
                be compiled and linked to with the
                libsystemd-journal
                pkg-config(1)
                file.