Child capture process exited: exited status 127

Since you are most likely using Bash, this is probably a "command not found" error. If I recall correctly, you should be getting a different error in the case that Wireshark can't start a capture, but it is possible that this is a path problem.

The "child capture process" is dumpcap, so the error likely means that dumpcap is not on your PATH. Try running which dumpcap. If there is no output then you need to add dumpcap to your path. The executable is usually in /usr/bin/ (if you used apt or synaptic to install Wireshark) or /usr/local/bin if you compiled Wireshark yourself. Normally, these directories are on your path, so it may be that dumpcap is in a different directory (which may be the case if you compiled Wireshark with a custom prefix or installed it to a nonstandard directory).