/etc/update-manager/release-upgrades

# Default behavior for the release upgrader.

[DEFAULT]
# Default prompting 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

See also

• APT: wajig, apt-cache, add-apt-repository PPA, apt [ install | remove |purge | show | list | changelog | update | upgrade], do-release-upgrade, apt-mark, apt full-upgrade, sources.list, APT Automatic updates, unattended-upgrade, apt-transport-https, apt-get update, /etc/apt/, /etc/apt/apt.conf.d/50unattended-upgrades, /etc/apt/apt.conf.d/, /etc/apt/apt.conf.d/20auto-upgrades, apt-file, apt-utils