Hello friends, is it possible to update ISPConfig 3.1.1p1 in multiserver mode to the newest version and update Debian Jessie to the Buster at the same time? How do I proceed? Should I first update ISPconfig or Debian? Jessie is now unsupported and I'm affraid ISPconfig. I'm afraid ISPconfig will crash after the Debian update.
Generally, yes. But Debian 10 is not supported by ISPConfig yet, so updating now will crash your system. Please wait until Buster gets released and we announce that it is supported by ISPConfig.
While waiting on Buster, you could perform the intermediate upgrade to stretch and get on the latest ISPConfig version. The ISPConfig update should be quite straightforward as you're on the same 3.1 point-release. The upgrade to stretch isn't bad, and there have been several posts outlining the steps to do so in the last year.
