>>> sudo do-release-upgrade
Checking for a new Ubuntu release
Get:1 Upgrade tool signature [819 B]
Get:2 Upgrade tool [1,239 kB]
Fetched 1,240 kB in 0s (0 B/s)
authenticate 'bionic.tar.gz' against 'bionic.tar.gz.gpg'
extracting 'bionic.tar.gz'

Reading cache
pcilib: Cannot open /proc/bus/pci
lspci: Cannot find any working access method.

Checking package manager

Can not upgrade

Your python3 install is corrupted. Please fix the '/usr/bin/python3'
symlink.

原因是python软链接到了python3，改回python2就行了

sudo ln -s /usr/bin/python2 /usr/bin/python