The KEY connector has three contacs -Ground, Contact 1, Contact 2.
Make a short circuit between contact and ground for using.
In simple mode, CW, Contact 1 is straight key, Contact 2 PTT.
In iambic mode CW, Contact 1 is Dot, Contact 2 is Dash
In SSB and other modes, both contacts are PTT.
Iambic mode can use with PowerSDR, ZeusRadio and QUISK + OKM ( Odyssey Key Master)
All this programms work under Windows.
Under Linux try to use GHPSDR Ghpsdr3 - HPSDRwiki
or QT Radio QtRadio - Operation - Ghpsdr3 SDR project