It looks like there was an issue communicating with the mirror of the Ubuntu archive which you use. You'll need to sort this out yourself or switch mirrors. From VarLogDistupgradeMainlog.txt:
32 2019-05-14 17:56:19,426 DEBUG Checking pkg: ubuntu-standard 33 2019-05-14 17:56:19,429 DEBUG examining: 'deb-src http://ftp.sjtu.edu.cn/ubuntu/ cosmic main restricted #Added by software-properties' 34 2019-05-14 17:56:19,429 DEBUG verifySourcesListEntry: deb-src http://ftp.sjtu.edu.cn/ubuntu/ disco main restricted #Added by software-prop erties 35 2019-05-14 17:56:19,429 DEBUG url_downloadable: http://ftp.sjtu.edu.cn/ubuntu//dists/disco/Release 36 2019-05-14 17:56:19,429 DEBUG s='http' n='ftp.sjtu.edu.cn' p='/ubuntu//dists/disco/Release' q='' f='' 37 2019-05-14 17:56:24,501 DEBUG error from httplib: 'Remote end closed connection without response' ** Changed in: ubuntu-release-upgrader (Ubuntu) Status: New => Incomplete -- You received this bug notification because you are a member of Ubuntu Bugs, which is subscribed to Ubuntu. https://bugs.launchpad.net/bugs/1828990 Title: distro update failed, no valid mirrors available. To manage notifications about this bug go to: https://bugs.launchpad.net/ubuntu/+source/ubuntu-release-upgrader/+bug/1828990/+subscriptions -- ubuntu-bugs mailing list [email protected] https://lists.ubuntu.com/mailman/listinfo/ubuntu-bugs
