问Docker错误: ln:目标'ps‘不是目录

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RUN mkdir build run logs frontend/dist \
    && apt-get -y install curl \
    ...
    && ln -s /usr/bin/esmtp /usr/sbin/sendmaildocker ps

ebconf: unable to initialize frontend: Dialog
debconf: (TERM is not set, so the dialog frontend is not usable.)
debconf: falling back to frontend: Readline
debconf: unable to initialize frontend: Readline
debconf: (This frontend requires a controlling tty.)
debconf: falling back to frontend: Teletype
Processing triggers for libc-bin (2.19-0ubuntu6.9) ...
ln: target 'ps' is not a directory
The command '/bin/sh -c mkdir build run logs frontend/dist     && apt-get -y install curl     && curl -sL https://deb.nodesource.com/setup_6.x | sudo -E bash -     && apt-get install -y nodejs   && npm install gulp bower        && npm cache clean      && npm set progress=false       && npm install --prefix frontend        && apt-get update && apt-get install -y esmtp   && ln -s /usr/bin/esmtp /usr/sbin/sendmaildocker ps' returned a non-zero code: 1