man iftop Command

Man page for apt-get iftop Command

Man Page for iftop in Linux

This tutorial shows the man page for man iftop in linux.

Open terminal with 'su' access and type the command as shown below:
man iftop

Result of the Command Execution shown below:

IFTOP(8)                                                                                                                                                    IFTOP(8)



NAME
       iftop   display bandwidth usage on an interface by host


SYNOPSIS
       iftop  h | [ nNpbBP] [ i interface] [ f filter code] [ F net/mask]


DESCRIPTION
       iftop listens to network traffic on a named interface, or on the first interface it can find which looks like an external interface if none is specified, and
       displays a table of current bandwidth usage by pairs of hosts.  iftop must be run with sufficient permissions to monitor all network traffic  on  the  inter Äê
       face; see pcap(3) for more information, but on most systems this means that it must be run as root.

       By default, iftop will look up the hostnames associated with addresses it finds in packets. This can cause substantial traffic of itself, and may result in a
       confusing display. You may wish to suppress display of DNS traffic by using filter code such as not port domain, or switch it off entirely, by using  the   n
       option or by pressing n when the program is running.

       By  default, iftop counts all IP packets that pass through the filter, and the direction of the packet is determined according to the direction the packet is
       moving across the interface.  Using the  F option it is possible to get iftop to show packets entering and leaving a given network.  For  example,  iftop   F
       10.0.0.0/255.0.0.0 will analyse packets flowing in and out of the 10.* network.

       Some other filter ideas:

       not ether host ff:ff:ff:ff:ff:ff
              Ignore ethernet broadcast packets.

       port http and not host webcache.example.com
              Count web traffic only, unless it is being directed through a local web cache.

       icmp   How much bandwidth are users wasting trying to figure out why the network is slow?


OPTIONS
        h     Print a summary of usage.

        n     Don't do hostname lookups.

        N     Do not resolve port number to service names

        p     Run in promiscuous mode, so that traffic which does not pass directly through the specified interface is also counted.

        P     Turn on port display.

        b     Don't display bar graphs of traffic.

        B     Display bandwidth rates in bytes/sec rather than bits/sec.

        i interface
              Listen to packets on interface.

        f filter code
              Use filter code to select the packets to count. Only IP packets are ever counted, so the specified code is evaluated as (filter code) and ip.

        F net/mask
              Specifies  a network for traffic analysis.  If specified, iftop will only include packets flowing in to or out of the given network, and packet direc Äê
              tion is determined relative to the network boundary, rather than to the interface.  You may specify mask as a dotted quad, such as /255.255.255.0,  or
              as a single number specifying the number of bits set in the netmask, such as /24.

        c config file
              Specifies an alternate config file.  If not specified, iftop will use ~/.iftoprc if it exists.  See below for a description of config files


DISPLAY
       When  running,  iftop uses the whole screen to display network usage. At the top of the display is a logarithmic scale for the bar graph which gives a visual
       indication of traffic.

       The main part of the display lists, for each pair of hosts, the rate at which data has been sent and received over the preceding 2, 10 and 40  second  inter Äê
       vals. The direction of data flow is indicated by arrows, <= and =>. For instance,

       foo.example.com  =>  bar.example.com      1Kb  500b   100b
                        <=                       2Mb    2Mb    2Mb

       shows,  on  the  first line, traffic from foo.example.com to bar.example.com; in the preceding 2 seconds, this averaged 1Kbit/s, around half that amount over
       the preceding 10s, and a fifth of that over the whole of the last 40s. During each of those intervals, the  data  sent  in  the  other  direction  was  about
       2Mbit/s.  On  the actual display, part of each line is inverted to give a visual indication of the 10s average of traffic.  You might expect to see something
       like this where host foo is making repeated HTTP requests to bar, which is sending data back which saturates a 2Mbit/s link.

       By default, the pairs of hosts responsible for the most traffic (10 second average) are displayed at the top of the list.

       At the bottom of the display, various totals are shown, including peak traffic over the last 40s, total traffic  transferred  (after  filtering),  and  total
       transfer rates averaged over 2s, 10s and 40s.


SOURCE / DEST AGGREGATION
       By  pressing s or d while iftop is running, all traffic for each source or destination will be aggregated together.  This is most useful when iftop is run in
       promiscuous mode, or is run on a gateway machine.


PORT DISPLAY
       S or D toggle the display of source and destination ports respectively. p will toggle port display on/off.


DISPLAY TYPE
       t cycles through the four line display modes; the default 2 line display, with sent and received traffic on separate lines, and 3 1 line displays, with sent,
       received, or total traffic shown.


DISPLAY ORDER
       By  default,  the  display is ordered according to the 10s average (2nd column).  By pressing 1, 2 or 3 it is possible to sort by the 1st, 2nd or 3rd column.
       By pressing < or > the display will be sorted by source or destination hostname respectively.


DISPLAY FILTERING
       l allows you to enter a POSIX extended regular expression that will be used to filter hostnames shown in the display.  This is a good way  to  quickly  limit
       what is shown on the display.  Note that this happens at a much later stage than filter code, and does not affect what is actually captured.  Display filters
       DO NOT affect the totals at the bottom of the screen.


PAUSE DISPLAY / FREEZE ORDER
       P will pause the current display.

       o will freeze the current screen order.  This has the side effect that traffic between hosts not shown on the screen at the time will not be  shown  at  all,
       although it will be included in the totals at the bottom of the screen.


SCROLL DISPLAY
       j and k will scroll the display of hosts.  This feature is most useful when the display order is frozen (see above).


FILTER CODE
       f allows you to edit the filter code whilst iftop running.  This can lead to some unexpected behaviour.


CONFIG FILE
       iftop  can read its configuration from a config file.  If the  c option is not specified, iftop will attempt to read its configuration from ~/.iftoprc, if it
       exists.  Any command line options specified will override settings in the config file.

       The config file consists of one configuration directive per line.  Each directive is a name value pair, for example:

       interface: eth0

       sets the network interface.  The following config directives are supported:


       interface: if
              Sets the network interface to if.

       dns resolution: (yes|no)
              Controls reverse lookup of IP addresses.

       port resolution: (yes|no)
              Controls conversion of port numbers to service names.

       filter code: bpf
              Sets the filter code to bpf.

       show bars: (yes|no)
              Controls display of bar graphs.

       promiscuous: (yes|no)
              Puts the interface into promiscuous mode.

       port display: (off|source only|destination only|on)
              Controls display of port numbers.

       hide source: (yes|no)
              Hides source host names.

       hide destination: (yes|no)
              Hides destination host names.

       use bytes: (yes|no)
              Use bytes for bandwidth display, rather than bits.

       sort: (2s|10s|40s|source|destination)
              Sets which column is used to sort the display.

       line display: (two line|one line both|one line sent|one line received)
              Controls the appearance of each item in the display.

       show totals: (yes|no)
              Shows cumulative total for each item.

       log scale: (yes|no)
              Use a logarithmic scale for bar graphs.

       max bandwidth: bw
              Fixes the maximum for the bar graph scale to bw, e.g. "10M". Note that the value has to always be in bits, regardless if  the  option  to  display  in
              bytes has been chosen.

       net filter: net/mask
              Defines an IP network boundary for determining packet direction.

       screen filter: regexp
              Sets a regular expression to filter screen output.


QUIRKS (aka they're features, not bugs)
       There  are  some circumstances in which iftop may not do what you expect.  In most cases what it is doing is logical, and we believe it is correct behaviour,
       although I'm happy to hear reasoned arguments for alternative behaviour.

       Totals don't add up

       There are several reasons why the totals may not appear to add up.  The most obvious is having a screen filter in effect, or screen ordering frozen.  In this
       case some captured information is not being shown to you, but is included in the totals.

       A  more  subtle  explanation  comes  about  when running in promiscuous mode without specifying a  F option.  In this case there is no easy way to assign the
       direction of traffic between two third parties.  For the purposes of the main display this is done in an arbitrary fashion (by ordering of IP addresses), but
       for  the sake of totals all traffic between other hosts is accounted as incoming, because that's what it is from the point of view of your interface.  The  F
       option allows you to specify an arbitrary network boundary, and to show traffic flowing across it.

       Peak totals don't add up

       Again, this is a feature.  The peak sent and peak received didn't necessarily happen at the same time.  The peak total is the maximum of sent  plus  received
       in each captured time division.

       Changing the filter code doesn't seem to work

       Give it time.  Changing the filter code affects what is captured from the time that you entered it, but most of what is on the display is based on some frac Äê
       tion of the last 40s window of capturing.  After changing the filter there may be entries on the display that are disallowed by the current filter for up  to
       40s.  DISPLAY FILTERING has immediate effect and does not affect what is captured.


FILES
       ~/.iftoprc
              Configuration file for iftop.


SEE ALSO
       tcpdump(8), pcap(3), driftnet(1).


AUTHOR
       Paul Warren <pdw@ex parrot.com>


VERSION
       $Id: iftop.8,v 1.25 2005/12/25 11:50:21 pdw Exp $


COPYING
       This  program  is free software; you can redistribute it and/or modify it under the terms of the GNU General Public License as published by the Free Software
       Foundation; either version 2 of the License, or (at your option) any later version.

       This program is distributed in the hope that it will be useful, but WITHOUT ANY WARRANTY; without even the implied warranty of MERCHANTABILITY or FITNESS FOR
       A PARTICULAR PURPOSE. See the GNU General Public License for more details.

       You should have received a copy of the GNU General Public License along with this program; if not, write to the Free Software Foundation, Inc., 675 Mass Ave,
       Cambridge, MA 02139, USA.




                                                                                                                                                            IFTOP(8)-

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