煎炸熊の記事本

Source: How to trace networking activity of a command?

netstat for simplicity

Using netstat and grepping on the PID or process name:

# netstat -np --inet | grep "thunderbird"
tcp        0      0 192.168.134.142:45348   192.168.138.30:143      ESTABLISHED 16875/thunderbird
tcp        0      0 192.168.134.142:58470   192.168.138.30:443      ESTABLISHED 16875/thunderbird

And you could use watch for dynamic updates:

watch 'netstat -np --inet | grep "thunderbird"'

With:

• -n: Show numerical addresses instead of trying to determine symbolic host, port or user names
• -p: Show the PID and name of the program to which each socket belongs.
• --inet: Only show raw, udp and tcp protocol sockets.

strace for verbosity

You said you tried the strace tool, but did you try the option trace=network? Note that the output can be quite verbose, so you might need some grepping. You could start by grepping on "sin_addr".

 strace -f -e trace=network <your command> 2>&1 | grep sin_addr

Or, for an already running process, use the PID:

 strace -f -e trace=network -p <PID> 2>&1 | grep sin_addr