最近用上了archlinux，挺不错，不过升级系统的时候，出现错误，mtab有冲突，如果删除，又会出现空间不够的错误。google到了解决方法，如下：

When upgrading to filesystem-2011.12 there will be a conflict with /etc/mtab.

Install the package as follows:

pacman -S filesystem --force

It is strongly advised to avoid the --force or -f switch as it is not safe. However, in this particular case it is needed as deleting /etc/mtab manually would break pacman.

The reason for the conflict is that the file used to be generated at boot and hence not owned by any package. Now it is a symlink to /proc/self/mounts owned by filesystem. This change means that initscripts no longer requires write access to the rootfs (though other packages might).

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

最近ubuntu一直无法更新，开始也没注意，过去很久了一直不能更新。今天抽空看了一下，原来是proxy的问题。

错误提示是：Connection failed [IP: 127.0.0.1 8080]

解决办法是：

将/etc/apt/apt.conf文件里面有关代理的设置删掉。

OK。