如何清理docker产生的垃圾文件

无意中感觉磁盘空间不够用，于是使用df -a命令查看，结果令人大吃一惊，全是docker干的好事，在/var/lib/docker/aufs里生成了一堆垃圾：

davidhopper@davidhopper-ThinkPad-P50s:~$ df -a文件系统     1K-块   已用  可用 已用% 挂载点sysfs         0    0    0   - /sysproc         0    0    0   - /procudev      8112832    0 8112832  0% /devdevpts        0    0    0   - /dev/ptstmpfs      1627828   9580 1618248  1% /run/dev/sda6   84293120 77948404 2039772  98% /securityfs      0    0    0   - /sys/kernel/securitytmpfs      8139124  18040 8121084  1% /dev/shmtmpfs       5120    4  5116  1% /run/locktmpfs      8139124    0 8139124  0% /sys/fs/cgroupcgroup        0    0    0   - /sys/fs/cgroup/systemdpstore        0    0    0   - /sys/fs/pstoreefivarfs       0    0    0   - /sys/firmware/efi/efivarscgroup        0    0    0   - /sys/fs/cgroup/net_cls,net_priocgroup        0    0    0   - /sys/fs/cgroup/perf_eventcgroup        0    0    0   - /sys/fs/cgroup/cpu,cpuacctcgroup        0    0    0   - /sys/fs/cgroup/pidscgroup        0    0    0   - /sys/fs/cgroup/devicescgroup        0    0    0   - /sys/fs/cgroup/cpusetcgroup        0    0    0   - /sys/fs/cgroup/rdmacgroup        0    0    0   - /sys/fs/cgroup/blkiocgroup        0    0    0   - /sys/fs/cgroup/hugetlbcgroup        0    0    0   - /sys/fs/cgroup/freezercgroup        0    0    0   - /sys/fs/cgroup/memorysystemd-1       -    -    -   - /proc/sys/fs/binfmt_miscdebugfs        0    0    0   - /sys/kernel/debugmqueue        0    0    0   - /dev/mqueuehugetlbfs       0    0    0   - /dev/hugepagesfusectl        0    0    0   - /sys/fs/fuse/connectionsconfigfs       0    0    0   - /sys/kernel/config/dev/sda1    262144  33084 229060  13% /boot/efibinfmt_misc      0    0    0   - /proc/sys/fs/binfmt_misctmpfs      1627828    56 1627772  1% /run/user/1000gvfsd-fuse      0    0    0   - /run/user/1000/gvfs/dev/sda6   84293120 77948404 2039772  98% /var/lib/docker/aufs