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iftop Introduction

iftop is a text console-based network traffic monitor. It shows your server's per-connection traffic and bandwidth statistics.

Using iftop

dnf -y install epel-release
dnf -y install iftop

The options of the iftop command follow.

Options Description
-n Avoids hostname lookups
-N Avoids resolving port numbers to service names
-p Runs in promiscuous mode, so all traffic is counted
-P Displays the port numbers for connections
-l Displays and counts traffic to or from link-local IPv6 addresses
-b Doesn't display bar graphs for traffic
-m LIMIT Sets an upper limit for the bandwidth graph, specified as a number and a unit suffix
-u UNIT Displays traffic rates with the given unit
-B UNIT Synonym for -u
-i INTERFACE Interface to measure
-f FILTER CODE Uses the following filter code
-F NET/MASK Only measures traffic going to the specified IPv4 network
-G NET/MASK Only measures traffic going to the specified IPv6 network
-c config Uses the following configuration file
-t Uses non-ncurses mode

The units for the -M flag are as follows:

Unit Meaning
K Kilo
M Mega
G Giga

The units for the -u flag are as follows:

Unit Meaning
bit bits per second
bytes bytes per second
packets packets per second

A sample output from the author's home server running a Tor relay:

 Listening on bridge b          25.0Kb          37.5Kb          50.0Kb    62.5Kb
tt.neelc.org               => X.X.X.X                    13.5Mb  13.5Mb  13.5Mb
                           <=                             749Kb   749Kb   749Kb
tt.neelc.org               => X.X.X.X                    6.21Mb  6.21Mb  6.21Mb
                           <=                             317Kb   317Kb   317Kb
tt.neelc.org               => X.X.X.X                    3.61Mb  3.61Mb  3.61Mb
                           <=                             194Kb   194Kb   194Kb
tt.neelc.org               => X.X.X.X                     181Kb   181Kb   181Kb
                           <=                            3.36Mb  3.36Mb  3.36Mb
tt.neelc.org               => X.X.X.X                     151Kb   151Kb   151Kb
                           <=                            3.24Mb  3.24Mb  3.24Mb
tt.neelc.org               => X.X.X.X                    2.97Mb  2.97Mb  2.97Mb
                           <=                             205Kb   205Kb   205Kb
tt.neelc.org               => X.X.X.X                     156Kb   156Kb   156Kb
                           <=                            2.97Mb  2.97Mb  2.97Mb
tt.neelc.org               => X.X.X.X                    2.80Mb  2.80Mb  2.80Mb
                           <=                             145Kb   145Kb   145Kb
tt.neelc.org               => X.X.X.X                     136Kb   136Kb   136Kb
                           <=                            2.45Mb  2.45Mb  2.45Mb
TX:             cum:   30.1MB   peak:    121Mb  rates:    121Mb   121Mb   121Mb
RX:                    30.4MB            122Mb            122Mb   122Mb   122Mb
TOTAL:                 60.5MB            242Mb            242Mb   242Mb   242Mb

Breaking the bottom pane's lines:

  • TX - Transmit/upload data usage
  • RX - Receive/download data usage
  • TOTAL - Combined upload/download usage

Shortcut keys for interaction

  • S - aggregates all traffic for each source
  • D - aggregates all traffic for each destination
  • Shift+S - toggles display of the source port
  • Shift+D - toggles display of destination port
  • T - toggles between display modes: default two-line display with send and receive traffic and three-line display of send, receive, and total traffic
  • 1, 2, 3 - sort by 1st, 2nd, or 3rd column
  • L - enters a POSIX regular expression to filter hostnames
  • Shift+P - pauses current display
  • O - freezes total bandwidth counts
  • J - scrolls down
  • K - scrolls up
  • F - edits the filter code

Author: Neel Chauhan

Contributors: Ganna Zhyrnova, Steven Spencer