执行#pacman -Syu升级archlinux的时候，出现错误：

filesystem: /etc/mtab exists in filesystem
Errors occurred, no packages were upgraded.

发现在archlinux.org主页上有这个问题的解决方法：

http://www.archlinux.org/news/filesystem-upgrade-manual-intervention-required/

# pacman -S filesystem –force

Ok，然后

#pacman -Syu

成功升级。