ubuntu出现错误:E: Problem executing scripts APT::Update::Post-Invoke-Success 'if /usr/bin/test -w /var/
解决方法:
在终端执行如下几条命令：
sudo pkill -KILL appstreamcli
wget -P /tmp https://launchpad.net/ubuntu/+archive/primary/+files/appstream_0.9.4-1ubuntu1_amd64.deb https://launchpad.net/ubuntu/+archive/primary/+files/libappstream3_0.9.4-1ubuntu1_amd64.deb
sudo dpkg -i /tmp/appstream_0.9.4-1ubuntu1_amd64.deb /tmp/libappstream3_0.9.4-1ubuntu1_amd64.deb 问题即可解决。