一款实时流量监控工具
iftop命令 是一款实时流量监控工具，监控TCP/IP连接等，缺点就是无报表功能。必须以root身份才能运行。
iftop(选项)
iftop: display bandwidth usage on an interface by host
Synopsis: iftop -h | [-npblNBP] [-i interface] [-f filter code]
[-F net/mask] [-G net6/mask6]
-h display this message
-n don't do hostname lookups
-N don't convert port numbers to services
-p run in promiscuous mode (show traffic between other
hosts on the same network segment)
-b don't display a bar graph of traffic
-B Display bandwidth in bytes
-i interface listen on named interface
-f filter code use filter code to select packets to count
(default: none, but only IP packets are counted)
-F net/mask show traffic flows in/out of IPv4 network
-G net6/mask6 show traffic flows in/out of IPv6 network
-l display and count link-local IPv6 traffic (default: off)
-P show ports as well as hosts
-m limit sets the upper limit for the bandwidth scale
-c config file specifies an alternative configuration file
-t use text interface without ncurses
Sorting orders:
-o 2s Sort by first column (2s traffic average)
-o 10s Sort by second column (10s traffic average) [default]
-o 40s Sort by third column (40s traffic average)
-o source Sort by source address
-o destination Sort by destination address
The following options are only available in combination with -t
-s num print one single text output afer num seconds, then quit
-L num number of lines to print
第一行为带宽，这里为1Mbit,不是字节哦. 连接列表，最后三列分别是2秒，10秒和40秒的平均流量
=>代表发送
<=代表接收 最后三行表示发送，接收和全部的流量， 第二列为你运行iftop到目前流量，第三列为高峰值，第四列为平均值。
iftop # 默认是监控第一块网卡的流量
iftop -i eth1 # 监控eth1
iftop -n # 直接显示IP, 不进行DNS反解析
iftop -N # 直接显示连接埠编号, 不显示服务名称
iftop -F 192.168.1.0/24 or 192.168.1.0/255.255.255.0 # 显示某个网段进出封包流量