In Linux you use odbcinst to register the data source, but you need to know where libtdsodbc.so is
On my Mac, it was put in
/opt/local/lib/libtdsodbc.so
If that's not where yours was installed, do this to find its location:
sudo find / -name "libtdsodbc.so"
Then create a file called "tds.driver.template" with the following inside:
[FreeTDS]
Description = Open source FreeTDS Driver
Driver =/opt/local/lib/libtdsodbc.so
Then run
sudo odbcinst -i -d -f tds.driver.template