int sd_journal_get_cutoff_realtime_usec(sd_journal *j, uint64_t *from, uint64_t *to);
int sd_journal_get_cutoff_monotonic_usec(sd_journal *j, sd_id128_t boot_id, uint64_t *from, uint64_t *to);
sd_journal_get_cutoff_monotonic_usec() retrieves the monotonic timestamps of the first and last entries accessible in the journal. It takes three arguments: the journal context object j, a 128-bit identifier for the boot boot_id, and two pointers to 64-bit unsigned integers to store the timestamps, from and to. The timestamps are 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. The function will return the timestamps for the boot identified by the passed boot ID. Either one of the two timestamp arguments may be passed as NULL in case the timestamp is not needed, but not both.
Locations pointed to by parameters from and to will be set only if the return value is positive, and obviously, the parameters are non-null.
These APIs are implemented as a shared library, which can be compiled and linked to with the libsystemd pkg-config(1) file.