我正在使用该sudo do-release-upgrade命令从 18.04 升级到 20.04.1。
有一次我收到了以下消息：
Could not calculate the upgrade
An unresolvable problem occurred while calculating the upgrade.
This was likely caused by:
* Unofficial software packages not provided by Ubuntu
Please use the tool 'ppa-purge' from the ppa-purge
package to remove software from a Launchpad PPA and
try the upgrade again.
该工具，ppa-purge需要提供具体ppaname或ppaowner作为输入。
我如何知道哪个 PPA 实际上导致了升级问题？