how to enable safeD ? dmd.conf ? dmd switch ?

[someone]

https://dlang.org/articles/safed.html
https://dlang.org/dmd-linux.html#switches
http://ddili.org/ders/d.en/functions_more.html

Neither man dmd nor man dmd.conf appear to have a related/switch 
setting.

Does it means safeD is achieved by placing @safe attributes all 
over the place ? Or is it achieved by setting some global switch 
elsewhere ? Am I missing something ?