Grab startup logcat

I have a problem at work , Want to grab the boot Log About China service init Of log Information , But by

adb reboot
adb wait-for-device
adb logcat > LOG.log

This method has been unable to catch , Later, this method was used to solve the problem , It is hereby recorded that .

First of all, in the background log:

logcat -c;logcat -v threadtime >/data/20-1.log&

pgrep composer // Find keywords composer In the process pid

kill composer_pid  //kill composer process

Through this method , Successfully capture the boot process information I want .