The lsof can be used to find the list of processes that have active sockets open.

Let us see the list of current TCP connections using netstat command.

[liz@techpulp ~]# netstat -nt
Active Internet connections (w/o servers)
Proto Recv-Q Send-Q Local Address               Foreign Address             State
tcp        0      0 192.168.20.24:40816         74.125.19.83:80             ESTABLISHED
tcp        0      0 192.168.20.24:43059         74.125.19.83:80             ESTABLISHED
[liz@techpulp ~]#

Now let us find which process has these TCP sockets open using lsof command.

[liz@techpulp ~]# /usr/sbin/lsof -i
COMMAND    PID   USER   FD   TYPE DEVICE SIZE NODE NAME
firefox-b 3288    liz   13u  IPv4 157814       TCP
                          liz.techpulp.com:43058->cf-in-f83.google.com:http (ESTABLISHED)
firefox-b 3288    liz   40u  IPv4 158205       TCP
                          liz.techpulp.com:43059->cf-in-f83.google.com:http (ESTABLISHED)
[liz@techpulp ~]#

So Firefox has two active sockets open to google.com