Você precisará de um sistema de 64 bits para que isso funcione;)
Primeiro, adicione o repositório Xenial MSSQL ao seu sistema:
$ sudo curl -o /etc/apt/sources.list.d/mssql-server.list https://packages.microsoft.com/config/ubuntu/16.04/mssql-server-2017.list
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 91 100 91 0 0 195 0 --:--:-- --:--:-- --:--:-- 195
$ curl https://packages.microsoft.com/keys/microsoft.asc | sudo apt-key add -
% Total % Received % Xferd Average Speed Time Time Time Current
Dload Upload Total Spent Left Speed
100 983 100 983 0 0 2337 0 --:--:-- --:--:-- --:--:-- 2340
OK
Em segundo lugar, atualize a lista de pacotes disponíveis do APT:
$ sudo apt-get update
Hit:1 http://ppa.launchpad.net/numix/ppa/ubuntu yakkety InRelease
Get:2 http://security.ubuntu.com/ubuntu yakkety-security InRelease [93,3 kB]
Hit:3 http://nl.archive.ubuntu.com/ubuntu yakkety InRelease
Hit:4 http://nl.archive.ubuntu.com/ubuntu yakkety-updates InRelease
Hit:5 http://nl.archive.ubuntu.com/ubuntu yakkety-backports InRelease
Get:6 https://packages.microsoft.com/ubuntu/16.04/mssql-server xenial InRelease [2828 B]
Get:7 https://packages.microsoft.com/ubuntu/16.04/mssql-server xenial/main amd64 Packages [940 B]
Fetched 97,1 kB in 0s (204 kB/s)
Reading package lists... Done
Opcionalmente, você pode verificar se está pronto para instalar:
$ apt-cache search mssql-server
mssql-server - Microsoft SQL Server Relational Database Engine
mssql-server-agent - Microsoft SQL Server Agent
mssql-server-fts - Microsoft SQL Server Full Text Search.
mssql-server-ha - The mssql-server-ha package contains HA extensions for the Microsoft SQL Server Relational Database Engine.
mssql-server-is - SSIS on Linux
Em seguida, basta instalar com sudo apt install mssql-server
.