Have you ever got stuck with an iptables unrecognized service?

Setting up a good firewall promises better security. And iptables is a preferred choice.

But, iptables errors are common and way too tricky to resolve. And, this error mainly occurs due to incorrect syntax of the commands used.

At Bobcares, we often receive requests to fix this error as part of our Server Management Services.

Today, let’s discuss this iptables error in detail and see some top fixes for it.

What is iptables unrecognized service?

Iptables is an extremely flexible firewall utility. Basically, it works based on a set of specified rules. These rules specify the action to take on server traffic.

So, when anyone tries to establish a connection to the server, iptables look for a rule in its list to match it to. If it doesn’t find one, it takes the default action. The action can be ALLOW, DENY or REJECT traffic.

Therefore managing Iptables involves playing with the different ruleset. And, such iptables start, stop or save requests often ends up in iptables unrecognized service error.

This mainly occurs when we use the wrong syntax for commands. It also occurs when the server uses a different firewall managing program.

How we fix the unrecognized service error?

Let’s now discuss some scenarios in which this error occurs and see how our Support Engineers fix it efficiently.

1. Firewall conflicts

Recently. one of our customers approached us with an iptables error. He was using Ubuntu server and tried to start the iptables using the command,

sudo service iptables start

But, every time it ended up showing the error

iptables: unrecognized service

He also tried the below commands,

apt-get install iptables-persistent
invoke-rc.d iptables-persistent save
service ufw start

However, it didn’t work. Our Support Engineers checked the error and found some firewall conflicts in the server.

As it was an Ubuntu server, it was using the default Ubuntu firewall manager instead of iptables. This created the problem. So, we had to disable the “UFW” using the command,

sudo ufw disable

Disabling the UFW and using iptables resolved the error.

Similarly, in the case of CentOS 7 servers, Firewalld also can be a reason for conflict. FirewallD is included by default with CentOS 7.

2. Incorrect syntax of commands

Sometimes, executing the below commands in Ubuntu server also returns an unrecognized service message,

service iptables save

This command works based on the startup script of iptables in the folder /etc/init.d. Usually, this command will work for RHEL/ Red Hat / CentOS. In Ubuntu, to save the changes in firewall rules, we use the following command

sudo /sbin/iptables-save

However, some customers insist on using the same command as before. So, we add custom executable startup scripts inside the /etc/init.d folder. This resolves the error effectively.

[Need more assistance to fix this error?- We’ll help you.]

Conclusion

In short, the iptables unrecognized service occurs due to conflict with firewall managing program, wrong iptables commands and so on. Today’s writeup discussed this error in detail and we saw how our Support Engineers fix it for customers.