发现arch下sudo没有自动补全了,然后找了下,发现跟bash-completion有关,解决方法,很简单,就是安装bash-completion,然后source下,当然这个source必须每次都要,所以写入.bashrc吧.

sudo pacman -S bash-completion
echo "source /etc/bash_completion" >>/home/$USER/.bashrc