Reference here: https://pubs.opengroup.org/onlinepubs/009695399/functions/timer_create.html DESCRIPTION ... Each implementation shall define a set of clocks that can be used as timing bases for per-process timers. All implementations shall support a clock_id of CLOCK_REALTIME. *** If the Monotonic Clock option is supported, implementations shall support a clock_id of CLOCK_MONOTONIC. *** ... Change-Id: Ia8e7302ed4a7e9ec11a0059bd68e9674ea942001 Signed-off-by: chao.an <anchao@xiaomi.com>