Since SQL Server was fist introduced, it has ever only run on Windows operating systems. Well with the announcement on March 7, 2016 this is set to change. Microsoft has announced SQL Server is being worked on to allow it to run on Linux. as of the announcement the release is being targeted for availability in mid-2017.
There is not a lot of information available for this release on what it will look like, but this is a significant step from Microsoft to allow customers who currently do not have the ability to utilise SQL Server will be able.
Microsoft are undertaking a private preview for selected customers. If you would like to stay uptodate with what is happening you can sign up for regular updates.
More information on the announcement is available at this SQL Server on Linux announcement.