메모리 부족 경고이다. echo 1 > /proc/sys/vm/drop_cachesecho 2 > /proc/sys/vm/drop_cachesecho 3 > /proc/sys/vm/drop_caches만약 permission denied가 나오면 다음을 입력한다.sudo sh -C 'echo 1 > /proc/sys/vm/drop_caches'sudo sh -C 'echo 2 > /proc/sys/vm/drop_caches'sudo sh -C 'echo 3 > /proc/sys/vm/drop_caches'