Logd default store in 19.07

i have linkit smart 7688 duo on openwrt 19.07.1. Where logd save log? i can't found nor uci or logd's opened file descriptors. The logs stored not in RAM because i can read previous boot log and maybe logs not save when incorrect shutdown

System and kernel logs are stored in RAM. They get destroyed at reboot.

Likely not. You get confused by the time stamps in the log, but that is caused by the absence of a real-time clock causing assumptions made about the date/time as the boot. Usually the log show initially the date/time of either the compilation of the firmware or the last modification to a file in /etc