How can I change iptable entries using bash script?

Question

I have an embedded Linux firmware running on a home router. When I run the following commands one by one from the terminal as root, it works without any errors and serves my purpose. I know this is not a secure policy. This is only to test something.

iptables -P INPUT ACCEPT
iptables -P FORWARD ACCEPT
iptables -P OUTPUT ACCEPT
iptables -F
iptables -X
iptables -A INPUT -p tcp -i eth1 --dport 4444 -j ACCEPT

However, when this is run in a bash script as root as below,

#!/bin/bash
iptables -P INPUT ACCEPT
iptables -P FORWARD ACCEPT
iptables -P OUTPUT ACCEPT
iptables -F
iptables -X
iptables -A INPUT -p tcp -i eth1 --dport 4444 -j ACCEPT

it gives the following error:

iptables: Bad policy name. Run `dmesg' for more information.
iptables: Bad policy name. Run `dmesg' for more information.
iptables: Bad policy name. Run `dmesg' for more information.
iptables: No chain/target/match by that name.
iptables: No chain/target/match by that name.

I have confirmed that the last line of bash script executes without errors and the entry can be seen in iptables. However, all the other lines throw an error. What am I doing wrong? Surprisingly, the same batch script works fine on my Ubuntu machine.

How did you run the shell script with root privilege? Can you let us know how you invoked it? — Inian
– Inian, Commented Dec 14, 2016 at 5:53
The router was shipped with telnet service running by default with default credentials. — bAd bOy
– bAd bOy, Commented Dec 14, 2016 at 6:04

etheranger · Accepted Answer · 2016-12-14 06:20:23Z

2

Did you create the script in Windows, or in some other way that gave it Windows line endings (CRLF) where the router is expecting Unix line endings (LF)?

That would lead to the interpreter reading an extra unprintable character on the end of each of the commands, which would give the errors shown.

You can check by running cat -v myScript.sh. Incorrect Windows line endings will show as:

iptables -P INPUT ACCEPT^M
iptables -P FORWARD ACCEPT^M
iptables -P OUTPUT ACCEPT^M
iptables -F^M
iptables -X^M
iptables -A INPUT -p tcp -i eth1 --dport 4444 -j ACCEPT

edited Dec 14, 2016 at 6:20

answered Dec 14, 2016 at 6:13

etheranger

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1 Comment

bAd bOy Over a year ago

Thank you so very much! That was exactly the problem!

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