Ubuntu Zesty no longer is a supported version of Ubuntu, you’ll need to update apt/sources.list to this:
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1 2 3 4 5 6 |
deb http://old-releases.ubuntu.com/ubuntu/ zesty main restricted universe multiverse deb http://old-releases.ubuntu.com/ubuntu/ zesty-updates main restricted universe multiverse deb http://old-releases.ubuntu.com/ubuntu/ zesty-security main restricted universe multiverse deb http://old-releases.ubuntu.com/ubuntu/ zesty-proposed main restricted universe multiverse deb http://old-releases.ubuntu.com/ubuntu/ zesty-backports main restricted universe multiverse |
Run apt-get clean all after updating that file and you’ll be able to upgrade as normal.