apt 被卸载

下载三个包

apt #2016-2018 libapt-pkg5.0 #2016-2018 ubuntu-keyring #20162018
https://www.ubuntuupdates.org/ #有两个包 apt libapt-pkg5.0
https://www.ubuntuupdates.org/package/core/bionic/main/base/libapt-pkg5.0 #第三个包 ubuntu-keyring

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执行完毕即可使用apt apt-get
dpkg -i ubuntu-keyring_2018.02.28_all.deb
dpkg -i libfs6_1.0.5-1_amd64.deb
dpkg -i apt_1.6.1_amd64.deb