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Simulates a low bandwidth, high-latency network connection

slow

This bash script offers quick shortcuts to simulate slower network connections. It is useful when you need to simulate a wireless network on a Linux network server, especially when you are using a virtual machine guest on your local machine or in the cloud.

slow 3G                   # Slow network on default eth0 down to 3G wireless speeds
slow reset                # Reset connection for default eth0 to normal
slow vsat --latency=500ms # Simulate satellite internet  with a high latency
slow dsl -b 1mbps         # Simulate DSL with a slower speed than the default
slow modem-56k -d eth0    # Simulate a 56k modem on the eth1 device. eth0 is unchanged.

Credits

Richard Bullington-McGuire richard@moduscreate.com wrote the script inspired by a UI suggestion from Mike Schwartz mike@moduscreate.com.

Stack Overflow and Superuser questions that helped:

An Aptivate blog post lent some inspiration, as did this script for throttling bandwidth.

Copyright 2012 Modus Create, Inc.
Permission is hereby granted, free of charge, to any person obtaining a copy of this software and associated documentation files (the "Software"), to deal in the Software without restriction, including without limitation the rights to use, copy, modify, merge, publish, distribute, sublicense, and/or sell copies of the Software, and to permit persons to whom the Software is furnished to do so, subject to the following conditions:
The above copyright notice and this permission notice shall be included in all copies or substantial portions of the Software.
THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
#!/bin/bash
#
# slow
#
# Simulates a low bandwidth, high-latency network connection
#
# Requires a Linux operating system with the 'tc' traffic control tool
#
# Author: Richard Bullington-McGuire <richard@moduscreate.com>
# Author: Mike Schwartz <mike@moduscreate.com>
#
# Copyright 2012 Modus Create, Inc.
#
# Permission is hereby granted, free of charge, to any person obtaining
# a copy of this software and associated documentation files (the
# "Software"), to deal in the Software without restriction, including
# without limitation the rights to use, copy, modify, merge, publish,
# distribute, sublicense, and/or sell copies of the Software, and to
# permit persons to whom the Software is furnished to do so, subject
# to the following conditions:
#
# The above copyright notice and this permission notice shall be included
# in all copies or substantial portions of the Software.
#
# THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS
# OR IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF
# MERCHANTABILITY, FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT.
# IN NO EVENT SHALL THE AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY
# CLAIM, DAMAGES OR OTHER LIABILITY, WHETHER IN AN ACTION OF CONTRACT,
# TORT OR OTHERWISE, ARISING FROM, OUT OF OR IN CONNECTION WITH THE
# SOFTWARE OR THE USE OR OTHER DEALINGS IN THE SOFTWARE.
VERSION=0.1
device=eth0
bandwidth=100kbps
latency=350ms
packetloss=
command=slow
retcode=0
PATH=/sbin:/bin:/usr/sbin:/usr/bin
if ! which tc > /dev/null; then
echo "Aborting: No 'tc' iptables firewall traffic conditioner found" 1>&2
echo "This requires the Linux iptables firewall." 1>&2
exit 1
fi
if [ $EUID -ne 0 ]; then
echo "Aborting: you must run this as root."
exit 2
fi
# Option processing courtesy of Stack Overflow question
# http://stackoverflow.com/questions/402377/using-getopts-in-bash-shell-script-to-get-long-and-short-command-line-options/7680682#7680682
# Questioner: gagneet http://stackoverflow.com/users/35416/gagneet
# Answer: http://stackoverflow.com/a/9899366
# Answerer: http://stackoverflow.com/users/375889/jakesandlund
while test $# -gt 0
do
case $1 in
# Normal option processing
-h | --help)
# usage and help
command=help
break
;;
-v | --version)
command=version
break
;;
-d | --device)
shift
DEVICE=$1
;;
-b | --bandwidth)
shift
bandwidth=$1
;;
-l | --latency)
shift
latency=$1
;;
-p | --packetloss)
shift
packetloss=$1
;;
# ...
# Special cases
--)
break
;;
--*)
# error unknown (long) option $1
;;
-?)
# error unknown (short) option $1
;;
#
# Shortcuts
AMPS)
command=slow
bandwidth=14kbps
latency=250ms
;;
EDGE|2.5G|GPRS)
command=slow
bandwidth=50kbps
latency=200ms
;;
3G)
command=slow
bandwidth=1000kbps
latency=200ms
;;
4G)
command=slow
bandwidth=10000kbps
latency=100ms
;;
modem-0.1k|modem-110)
command=slow
bandwidth=110bps
latency=350ms
;;
modem-0.3k|modem-300)
command=slow
bandwidth=300bps
latency=300ms
;;
modem-1.2k|modem-1200)
command=slow
bandwidth=1200bps
latency=280ms
;;
modem-2.4k|modem-2400)
command=slow
bandwidth=2400bps
latency=250ms
;;
modem-9.6k|modem-9600)
command=slow
bandwidth=9600bps
latency=200ms
;;
modem-14.4k|modem-14400)
command=slow
bandwidth=14400bps
latency=150ms
;;
modem-28.8k|modem-28800)
command=slow
bandwidth=28800bps
latency=150ms
;;
modem-56k|modem-56000)
command=slow
bandwidth=56kbps
latency=120ms
;;
56k)
command=slow
bandwidth=56kbps
latency=40ms
;;
T1|t1)
command=slow
bandwidth=1500kbps
latency=20ms
;;
T3|t3)
command=slow
bandwidth=45mbps
latency=10ms
;;
DSL|dsl)
command=slow
bandwidth=2mbps
latency=40ms
;;
cablemodem)
command=slow
bandwidth=10mbps
latency=20ms
;;
wifi-a|wifi-g)
command=slow
bandwidth=54mbps
latency=5ms
;;
wifi-b)
command=slow
bandwidth=11mbps
latency=10ms
;;
wifi-n)
command=slow
bandwidth=110mbps
latency=2ms
;;
vsat)
command=slow
bandwidth=5mbps
latency=500ms
;;
clear|reset)
command=clear
;;
status)
command=status
break
;;
# FUN STUFF HERE:
# Split apart combined short options
-*)
split=$1
shift
set -- $(echo "$split" | cut -c 2- | sed 's/./-& /g') "$@"
continue
;;
# Done with options
*)
break
;;
esac
# for testing purposes:
echo "param $1"
shift
done
echo "command=$command"
echo "bandwidth=$bandwidth"
echo "latency=$latency"
case $command in
help)
echo $0
echo 'Usage: slow <network-type> [-d device] [-b bandwidth] [-l latency] [-p drop]'
echo ' slow reset'
echo ' slow status'
echo
echo '"network-type" type can be:'
echo ' GPRS'
echo ' GSM'
echo ' EDGE'
echo ' 2.5G'
echo ' GPRS'
echo ' 3G'
echo ' 4G'
echo ' modem-2.4k'
echo ' modem-9.6k'
echo ' modem-14.4k'
echo ' modem-28.8k'
echo ' modem-56k'
echo ' 56k'
echo ' T1'
echo ' T3'
echo ' DSL'
echo ' cablemodem'
echo ' wifi-a'
echo ' wifi-b'
echo ' wifi-g'
echo ' wifi-n'
echo ' eth-10'
echo ' eth-100'
echo ' eth-1000'
echo ' vsat'
echo ' vsat-busy'
;;
version)
# version info
echo "slow version $VERSION"
echo "Copyright (c) 2012 Modus Create"
;;
slow)
# Credit to Superuser for the basic commands that run this
# Question: http://superuser.com/questions/147156/simulating-a-low-bandwidth-high-latency-network-connection-on-linux
# Author: Justin L. http://superuser.com/users/38740/justin-l
# Answer: http://superuser.com/a/147434/159810
if tc qdisc show dev $device | grep "qdisc htb 1: root" >/dev/null; then
verb=change
echo "Changing existing queuing discipline"
else
verb=add
echo "Adding new queuing discipline"
tc qdisc $verb dev $device root handle 1: htb default 12
fi
tc class $verb dev $device parent 1:1 classid 1:12 htb rate $bandwidth ceil $bandwidth &&
tc qdisc $verb dev $device parent 1:12 netem delay $latency
retcode=$?
;;
clear)
echo resetting queueing discipline
tc qdisc del dev $device root
retcode=$?
;;
status)
tc qdisc
retcode=$?
;;
esac
exit $retcode

FYI, my fork has incorporated changes from aloysiuschang, and also fixed some stuff.

https://gist.github.com/denilsonsa/5176e1c9b6a119594ce0

oliver commented Oct 21, 2015

According to http://lartc.org/manpages/tc.txt kbps means "Kilobytes per second". So maybe I'm being dense right now, but I think modem-56k should have "bandwidth=7kbps" or "bandwidth=56kbit" instead of "bandwidth=56kbps".
Same would go for just about all of the other settings - they are too high by factor 8?

Yes, @oliver is correct.

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