Ubuntu/Upgrade

Release Upgrade

sudo apt update
sudo apt -y upgrade
sudo do-release-upgrade

/usr/bin/do-release-upgrade

/etc/update-manager/release-upgrades

vim /etc/update-manager/release-upgrades

# Default behavior for the release upgrader.

[DEFAULT]
# Default prompting and upgrade behavior, valid options:
#
#  never  - Never check for, or allow upgrading to, a new release.
#  normal - Check to see if a new release is available.  If more than one new
#           release is found, the release upgrader will attempt to upgrade to
#           the supported release that immediately succeeds the
#           currently-running release.
#  lts    - Check to see if a new LTS release is available.  The upgrader
#           will attempt to upgrade to the first LTS release available after
#           the currently-running one.  Note that if this option is used and
#           the currently-running release is not itself an LTS release the
#           upgrader will assume prompt was meant to be normal.
Prompt=lts

Issues

Failed to connect to changelogs

Firewall issue

$ sudo do-release-upgrade
Checking for a new Ubuntu release
Failed to connect to https://changelogs.ubuntu.com/meta-release-lts. Check your Internet connection or proxy settings
There is no development version of an LTS available.
To upgrade to the latest non-LTS development release
set Prompt=normal in /etc/update-manager/release-upgrades.

/usr/lib/python3/dist-packages/UpdateManager/Core/MetaRelease.py - line 380

        # generic network error
        except (URLError, BadStatusLine, socket.timeout) as e:
            self._debug("result of meta-release download: '%s'" % e)
            print("Failed to connect to %s. Check your Internet connection "
                  "or proxy settings" % self.METARELEASE_URI)