Wireshark - Wireshark is a network protocol analyzer for Unix and Windows. It lets you capture and interactively browse the traffic running on a computer network.

strace - Trace system calls and signals. A diagnostic, debugging and instructional userspace utility.

tcpdump - tcpdump is a common packet analyzer that runs under the command line.

htop - htop - an interactive process viewer for Unix. This is htop, an interactive process viewer for Unix systems. It is a text-mode application (for console or X terminals) and requires ncurses. Latest release: htop 2.

netcat - Netcat is a featured networking utility which reads and writes data across network connections...

ftrace - A function tracer for the Linux kernel.