Linux Mint 19 will be based on the Ubuntu 18.04 LTS operating system
Clement Lefebvre, head of the Linux Mint project, disclosed in the project’s 2017 monthly issue that the development team will release the next major Linux Mint and LMDE soon.
With all versions of Linux Mint 18.3 “Sylvia” released, the Linux Mint team will focus on Linux Mint 19 and Linux Mint Debian Edition (LMDE) 3. Although LMDE 3 will be just a rollover installation image, all the latest Debian security updates are coming soon, and Linux Mint 19 will be released based on the Ubuntu 18.04 LTS (Bionic Beaver) operating system.
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Canonical will support Ubuntu 18.04 LTS (Bionic Beaver) and until April 2023, Linux Mint 19 will also be supported during the same period. Canonical has reduced support for the official Linux Mint KDE version, so next year there will be only Cinnamon, MATE and Xfce versions released by Linux Mint 19.