Which applications are using internet
Solution 1:
lsof -i
will list the applications that are accessing the network. There are some helpful examples in the man page but you might also want to look at Track network connections with LSOF on Linux.
Solution 2:
I found very useful next command that show only the names of applications that use internet connection (create internet traffic) at the moment:
netstat -lantp | grep -i stab | awk -F/ '{print $2 $3}' | sort | uniq
Source: Show apps that use internet connection at the moment (Multi-Language).