find -type d|xargs chmod 755
find -type f|xargs chmod 644

上面这个命令如果碰到带有空格的文件名会出错

find . -type d -exec chmod -fv 755 {} \;
find . -type f -exec chmod -fv 644 {} \;

https://askubuntu.com/questions/604489/what-are-the-default-permissions-of-directories-in-home-desktop-downloads-etc