Welcome to Adobe Community.
I am sorry but Captivate 6 is not supported on Linux Platform. It is only supported and available for Windows and Mac Platforms. Not sure how you are doing that.
One way to "record" on Linux would be to establish a remote connection to it. I'm guessing it would require some sort of terminal emulator software. Then you would run Captivate and record the screens on the PC remotely connected to the Linux machine.