android系统logcat日志重定向到kernel，可以通过串口来输出

修改system/core/rootdir/init.rc

chmod 0660 /sys/power/wake_lock
     chmod 0660 /sys/power/wake_unlock
 
+    chmod 0660 /proc/kmsg
     # Start logd before any other services run to ensure we capture all of their logs.
     start logd
+    start logota
     # Start lmkd before any other services run so that it can register them
     chown root system /sys/module/lowmemorykiller/parameters/adj
     chmod 0664 /sys/module/lowmemorykiller/parameters/adj
@@ -429,6 +431,7 @@ on load_persist_props_action
     load_persist_props
     start logd
     start logd-reinit
+    start logota
 
 # Indicate to fw loaders that the relevant mounts are up.
 on firmware_mounts_complete
@@ -1082,6 +1085,11 @@ service ueventd /system/bin/ueventd
     seclabel u:r:ueventd:s0
     shutdown critical
 
+service logota /system/bin/logcat -f /dev/kmsg *:D
+    class main
+    user root
+    group logd system
+

 service charge_logger /system/vendor/bin/charge_logger
     class main