RawCap is not available for Linux but there are a few alternatives that runs on Linux with similar functionality. The best Linux alternative is Wireshark, which is both free and Open Source. If that doesn't work for you, our users have ranked seven alternatives to RawCap, but unfortunately only two of them are available for Linux. If you can't find an alternative you can try to filter for web or SaaS options.
Wireshark is the world's foremost network protocol analyzer. It lets you capture and interactively browse the traffic running on a computer network. It is the de facto (and often de jure) standard across many industries and educational institutions.
tcpdump is a common packet analyzer that runs under the command line. It allows the user to intercept and display TCP/IP and other packets being transmitted or received over a network to which the computer is attached.