错误提示如下所示：
$ sudo apt update Hit:1 http://security.ubuntu.com/ubuntu bionic-security InRelease Hit:2 http://ca.archive.ubuntu.com/ubuntu bionic InRelease Hit:3 http://ca.archive.ubuntu.com/ubuntu bionic-updates InRelease Hit:4 http://ca.archive.ubuntu.com/ubuntu bionic-backports InRelease (appstreamcli:15814): GLib-CRITICAL **: g_strchug: assertion 'string != NULL' failed (appstreamcli:15814): GLib-CRITICAL **: g_strchomp: assertion 'string != NULL' failed (appstreamcli:15814): GLib-CRITICAL **: g_strchug: assertion 'string != NULL' failed (appstreamcli:15814): GLib-CRITICAL **: g_strchomp: assertion 'string != NULL' failed AppStream cache update completed, but some metadata was ignored due to errors. Reading package lists... Done Building dependency tree Reading state information... Done 1675 packages can be upgraded. Run 'apt list --upgradable' to see them.
解决办法：
sudo sed -i -e 's/bionic/xenial/g' /etc/apt/sources.list