在终端输入即可，注意.和/之间的空格
. /etc/bash_completion
这样就可以了，但是重启又不行，找到root的配置文件修改即可
找到 /root/.bashrc文件进行编辑，最后的三行
# enable programmable completion features (you don't need to enable
# this, if it's already enabled in /etc/bash.bashrc and /etc/profile
# sources /etc/bash.bashrc).
if [ -f /etc/bash_completion ] && ! shopt -oq posix; then
. /etc/bash_completion
fi
注释掉如上即可，exit退出再来就可以了