在创建dockerFile文件中出现/bin/sh: rm: command not found

通过学习dockerfile命令试着自己做一下练习，在联系过程中出现 /bin/sh: rm: command not found
代码

FROM centos:latest
MAINTAINER my<my@163.com>
ENV PATH /tmp
WORKDIR $PATH

RUN rm -rf /tmp

CMD /bin/bash

Build过程


Sending build context to Docker daemon 2.048 kB
Step 1/6 : FROM centos:latest
 ---> 1e1148e4cc2c
Step 2/6 : MAINTAINER my<my@163.com>
 ---> Running in dc6073af05a2
 ---> b6f7e3b7bca8
Removing intermediate container dc6073af05a2
Step 3/6 : ENV PATH /tmp
 ---> Running in 7d000413c304
 ---> f643d6b20259
Removing intermediate container 7d000413c304
Step 4/6 : WORKDIR $PATH
 ---> 340ef4b29f1c
Removing intermediate container 658c7d7a96b9
Step 5/6 : RUN rm -rf /tmp
 ---> Running in 3aad9ab202d1

/bin/sh: rm: command not found
The command '/bin/sh -c rm -rf /tmp' returned a non-zero code: 127

以上请大神指点迷津