Update/install fail: Server cannot access software repositories

If you are trying to install something and the server waits forever after you answer yes to the update and it accesses the software repository… something like…

apt-get update
...
details of packages
...
Need to get 83.7 MB of archives.
After this operation, 237 kB disk space will be freed.
Do you want to continue [Y/n]?
0% [Connecting to archive.ubuntu.com]

And then nothing. It fails.

Do you have UFW installed? UFW can block outgoing connections from your server, so it becomes unable to access the software repositories. Rather than make exceptions, it is easier to disable the firewall and enable again when update or install is done.
??
If you have UFW (Uncomplicated Firewall) installed, disable it and try again.

ufw disable

Now your upgrades should work. Once you are done, re-enable your firewall.

ufw enable