Upgrade to 16.04 failed. System says unstable repositories. Getting duplicate packages messages during updates
991
How can I fix apt error "W: Target Packages ... is configured multiple times"?
16578
How to upgrade a single package using apt-get?
40885
What should I do when I got the KEYEXPIRED error message after an apt-get update?
20710
Apt update fails at chrome stable main: "File has unexpected size (1103 != 1104). Mirror sync in progress?"
43579
I cannot install new packages: "Could not get lock /var/lib/dpkg/lock"
140893
Error when using apt-get update
144507
No facility exists in Update Manager to upgrade to a new version, why?
5820
How to fix the “Unable to calculate upgrade” issue from command line when upgrading from 12.04 to 14.04?
41519
What can I do if a package is not available on the newest version of Ubuntu (18.04) but is available on older versions?
2280
Package system is broken. How to fix it?
12534
14.04 --> 16.04 failed; apt (>= 1.0.1ubuntu2.13)' is not installed
154420
"Failed to download repository information" error
86777
Distribution upgrade problem "No new release found"
339
How to resolve "Failed to download repository information"?
4124
I cannot run apt update properly - apt update hangs
127196
"Error processing package" - apt upgrade cannot run due to package configuration errors
6105
What is the easiest way to resolve apt-get BADSIG GPG errors?