statのaccess/modify/changeの違い
last access: Time when file data last accessed. Changed by the mknod(2), utimes(2) and read(2) system calls.
last modified: Time when file data last modified. Changed by the mknod(2), utimes(2) and write(2) system calls.
last changed: Time when file status was last changed (inode data modification). Changed by the chmod(2), chown(2), link(2), mknod(2), rename(2), unlink(2), utimes(2) and write(2) system calls.