We are moving forward with a Linux apt mainstream servicing lifecycle for SQL Server 2017 and later:
For SQL Server 2017 and above we will only have Cumulative Update (CU) based General Distribution Releases (GDRs), thus simplifying it for users to download the required updates through one single branch which is the CU (Cumulative Update) branch. Users need to subscribe and use only one single repository, that is the CU repository, to get all the critical fixes, product improvements or bug fixes.
The RTM (Release to Manufacturing) based GDR repository that contained base SQL Server release, critical fixes and security updates since that release, will be removed. As they worked only for older Linux distributions (RHEL 7, Ubuntu 16.04 & SLES 12).
The RTM based GDR packages that were released for Ubuntu 16.04, RHEL 7 & SLES 12, the repos listed below will have no new releases, but will continue to be available