iftop命令 是一款實時流量監(jiān)控工具，監(jiān)控TCP/IP連接等，缺點就是無報表功能。必須以root身份才能運行。
語法：iftop(選項)
選項：
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
界面說明：
第一行為帶寬，這里為1Mbit,不是字節(jié)哦. 連接列表，最后三列分別是2秒，10秒和40秒的平均流量 => 代表發(fā)送
<= 代表接收 最后三行表示發(fā)送，接收和全部的流量， 第二列為你運行iftop到目前流量，第三列為高峰值，第四列為平均值。
實例：
iftop # 默認(rèn)是監(jiān)控第一塊網(wǎng)卡的流量
iftop -i eth1 # 監(jiān)控eth1
iftop -n # 直接顯示IP, 不進行DNS反解析
iftop -N # 直接顯示連接埠編號, 不顯示服務(wù)名稱
iftop -F 192.168.1.0/24 or 192.168.1.0/255.255.255.0 # 顯示某個網(wǎng)段進出封包流量