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I am trying to upgrade Ubuntu 16.04 to 18.04, but it hangs on "Reading cache":

$ sudo do-release-upgrade
Checking for a new Ubuntu release
Get:1 Upgrade tool signature [819 B]                                                                                                                                                                       
Get:2 Upgrade tool [1,246 kB]                                                                                                                                                                              
Fetched 1,247 kB in 0s (0 B/s)                                                                                                                                                                             
authenticate 'bionic.tar.gz' against 'bionic.tar.gz.gpg' 
extracting 'bionic.tar.gz'

Reading cache

The cursor sits blinking. Any idea what is wrong?

1 Answer 1

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I hit this same problem. After it prints "Reading cache" the CPU usage goes to 100% and stays there indefinitely. The underlying problem in my case was that /etc/apt/apt.conf was an empty directory instead of a file, which was causing do-release-upgrade to hang indefinitely. A sudo rmdir /etc/apt/apt.conf fixed my issue.

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    Thank you! That was it. How did you even figure this out? I couldn't find anyway to force it to dump some debug info.
    – randomizer
    Jun 4, 2019 at 1:40
  • @nlc I read some other StackOverflow answer that mentioned changing the contents of that file. When I tried to cat it to see what it currently had in it, I realized it wasn't a file at all. And on another working Ubuntu system it was missing entirely, so I opted to just delete it and that worked. Glad it solved your issue too! Seems the Ubuntu folks should figure out what created that directory in the first place and should fix do-release-upgrade so it doesn't hang in the case where it's improperly a directory. Jun 5, 2019 at 9:06

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