Tcp open port linux

Redhat / CentOS / Fedora Linux Open TCP/UDP Ports

Let us see how to open a port in the firewall on CentOS or RHEL version 5.x/6.x and 7.x including the latest version of Fedora Linux 27 or above.

How to open TCP port 80 on a RHEL/CentOS Linux

Open flle /etc/sysconfig/iptables:
# vi /etc/sysconfig/iptables
Append rule as follows:
-A RH-Firewall-1-INPUT -m state —state NEW -m tcp -p tcp —dport 80 -j ACCEPT
Save and close the file. Restart iptables:
# /etc/init.d/iptables restart

Open port TCP port # 110 on a RHEL

Append rule as follows:
-A RH-Firewall-1-INPUT -m state —state NEW -m tcp -p tcp —dport 110 -j ACCEPT

Open port 143 on a CentOS

Append rule as follows:
-A RH-Firewall-1-INPUT -m state —state NEW -m tcp -p tcp —dport 143 -j ACCEPT

Restart iptables service

Type the following command:
# service iptables restart

A note about opening a port on CentOS/RHEL 6

You can also use the iptable command as follows to open port 443:
# iptables -I INPUT -p tcp -m tcp —dport 443 -j ACCEPT
# service iptables save

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A note about Red Hat Enterprise Linux 7.x and CentOS 7.x

Above commands or files won’t work on RHEL/CentOS 7.x or the latest version of Fedora Linux. To see current open ports, type:
# firewall-cmd —list-ports
Find list of zones:
# firewall-cmd —get-zones
Sample outputs:

To find about interface name use ip command:
$ ip a
Sample outputs:

To get info about eth0 interface:
# firewall-cmd —get-zone-of-interface=eth0
Sample outputs:

Type the following command to open TCP port 80 for Apache/httpd server:
# firewall-cmd —permanent —add-port 80/tcp
To list open port again, type:
# firewall-cmd —list-ports
Sample outputs:

To open port range between 2000-3000/tcp, enter:
# firewall-cmd —permanent —add-port 2000-3000/tcp
Command to start/stop/restart firewall:
# systemctl start firewalld
# systemctl stop firewalld
# systemctl restart firewalld
# systemctl status firewalld
Sample outputs:

Verify that port is open

Run following command ss command/netstat command:
# netstat -tulpn | less
OR
# ss -tulpn | less
Make sure iptables is allowing port 80 / 110 / 143 connections by listing rules:
# iptables -L -n -v
Please refer to iptables man page for more information about iptables usage and syntax:
man iptables
man firewall-cmd

See also

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Comments on this entry are closed.

Save and close the file. Restart iptables:
# /etc/init.d/iptables restart

How to close and save a file.

LOL, if you can’t even navigate in a *nix environment why do you even bother with iptables?

nevertheless you can do the following:

1-insert rules you want
2- press Esc
3- press :
4- wq
5- Enter

save and close a file in VI
hit ESC
type :
type x

-A RH-Firewall-1-INPUT -m state –state NEW -m tcp -p tcp –dport 587 -j ACCEPT

hi i used this code in fedora 5 to open up the port 587 in my firewall so sendmail would work using this vi command below:

then i applied the changes and restarted the firewall as you metioned above, ok poped up for all selections. did i do this ok? let me know and thanks. rich.

I wonder what is happening on my newly installed centos5.2 as all connections excepts icmp are periodically refused (up and down in un-orderly fashion)

Please advice whats wrong; action taken
#service iptables stop
#chkconfig iptables off
#chkconfig –del iptables
#mkdir /backup
#mv /etc/init.d/iptables /backup/
#mv /etc/init.d/ip6tables /backup/
#init 6

Yet the connection refuse error keep on happening time to time(more frequently that connected)

You must be using another firewall script such as apf. Most hosting companies install something like this.

Don’t forget to make sure the ACCEPT lines are before any REJECT lines

MOVING the REJECTs to end of file or Above COMMIT Worked for me.

Helped me too. Thanks

good site, helped me a lot to restart a port in linux 5

An application that I use has an in-built Tcl webserver that uses ports 8015/8016. Is there a way to open these ports but at the same time restrict access to only selected IP addresses?

Sweet! I needed to open a port for the Sybase database server I installed on this box. Your instructions worked perfectly. Thanks for taking the time to post these instructions.

THank you so much buddy. That really helped.

Or, you can just run “system-config-securitylevel” and do it the easy way. 🙂
I always hated iptables commands.

thankyou now i can open port 80 🙂

I don’t seem to have a file called iptables.

When I create it in /etc/sysconfig and add one of those lines at the top, I get an error upon restart saying

“Applying iptables firewall rules: iptables-restore: line 1 failed”

Deleting that file again and restarting the service works fine. Any ideas?

Add your lines, ensuring that they appear before the final LOG and DROP lines for the RH-Firewall-1-INPUT chain. Do not add them at the top of the file.

For me, I needed to change the word RH-Firewall-1-INPUT to simply INPUT – I have CentOS 6.4. So, I ended up adding:

-A INPUT -m state –state NEW -m tcp -p tcp –dport 80 -j ACCEPT

I found that by using “iptables -F” followed by “service iptables save” I can generate this file. It then contians several rules – however LOG and DROP are not mentioned.

I’ve tried to add the lines in various places but get an error every time. I’m trying to accept incoming UDP traffic on a couple of ports for use with OSSEC.

the script line you advised for opening port 80 didn’t work for me!
this worked

-I INPUT -p tcp –dport 80 -j ACCEPT

Thanks this one worked for me too

Yup me too – needed to change RH-Firewall-1-INPUT to just INPUT

-A INPUT -m state –state NEW -m tcp -p tcp –dport 80 -j ACCEPT

I’ve made use of this article twice in as many weeks. Thanks!

I am Trying To Install Camfrog Server ( Linux Version ) On My Linus CentOS I can Wget And Install The App But Is Stuck After This Point Does Anyone KNow How to Install This App?

Hi iam totally a newbie to Linux, in my office i am assigned to this task which is install redhat enterprise server 5 and open up the ports 21,22 and 23 to someone else to access the box, he also needs to export the display to his machine as well, as this sounds “GREEK” to me, i need help from you guys to get this completed. pls tell me step by step what should i do?

i need to access java web service which is running on Apache in linux at port 8080 from windows.

Thanks a lot Vivek.

/etc/sysconfig/iptables-config: line 42: -A: command not found
/etc/sysconfig/iptables-config: line 43: -A: command not found

I am getting this error .

someone from outside my network is failing to access my linux server via SSH but i can access it using Putty from within my network. Nothing has changed on my router and there is no firewall in place to block the SSH connection, how can i allow that connection, the guy can ping the server and access other ports.

This information was very useful/handy to me today (2011-07-14) , 5 years after you wrote this article (SEPTEMBER 13, 2007) ! Thank you so much VIVEK GITE. Please keep posing such useful stuff. Regards.

thnx man work fine

I edited my /etc/sysconfig/iptables file. adding in the ports I needed to open. I successfully saved and closed the file, verifying the ports were added to file by viewing the iptables file. I then went to restart it with commands listed above. I kept getting command not found. The first line of the file reads: # Firewall configuration written by system-config-securitylevel
I am running RH Linux 2.6.18-53.el5. How do I stop and start the iptables process so the additional ports will take effect?

Can somebody help me? im trying these methods and they dont work

iptables: Setting chains to policy ACCEPT: filter [ OK ]
iptables: Unloading modules: [ OK ]
iptables: Applying firewall rules: iptables-restore: line 10 failed
[FAILED]
[root@ sysconfig]# nano iptables

and this is what i have in the file

# Generated by iptables-save v1.4.7 on Fri Sep 16 10:50:02 2011
*filter
:INPUT ACCEPT [0:0]
:FORWARD ACCEPT [0:0]
:OUTPUT ACCEPT [13:1276]
-A INPUT -m state –state RELATED,ESTABLISHED -j ACCEPT
-A INPUT -p icmp -j ACCEPT
-A INPUT -i lo -j ACCEPT
-A INPUT -p tcp -m state –state NEW -m tcp –dport 22 -j ACCEPT
-A INOUT -p tcp -m state –state NEW -m tcp –dport 80 -j ACCEPT
-A INPUT -j REJECT –reject-with icmp-host-prohibited
-A FORWARD -j REJECT –reject-with icmp-host-prohibited
COMMIT
# Completed on Fri Sep 16 10:50:02 2011

There was a TYPO my bad but i still cant get port 80 to listen.

iptables: Flushing firewall rules: [ OK ]
iptables: Setting chains to policy ACCEPT: filter [ OK ]
iptables: Unloading modules: [ OK ]
iptables: Applying firewall rules: [ OK ]
[root@ sysconfig]# telnet localhost 80
Trying ::1…
telnet: connect to address ::1: Connection refused
Trying 127.0.0.1…

sorry for the triple post after much googling and router configurations i figured it out

hi, thanks a bunch for an informative article. you literally saved my day today.
thanks again.

I have installed a sever with CentOS 6.0 and then installed mySQL and PHP in it. Then i installed CPanel in it. After rebooting the system, my Login screen is disabled and i can only login via Putty software on port 22 , and can only see a console screen.
My question is:
How can i gain access to my cpanel ? i read in articles that cpanel is accessed via 2082 and 2083 ports. But both are seemed to be blocked.

Thanks in advance. Please help

Terrific info. Very helpful. Thanks.

thanks a lot. it worked perfectly
God bless

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Easy steps to open a port in Linux RHEL/CentOS 7/8

Table of Contents

In this article I will share examples to check port status and open a port in Linux. This article was written while using CentOS 8, so it is safe to say that it also fully covers CentOS/RHEL 7/8, Fedora, Oracle Enterprise Linux and generally the whole Red Hat family of operating systems and possibly Novell’s SLES and OpenSUSE.

Before we jump into the examples to open a port in Linux, we must understand the requirement clearly. The very basic question which comes to my mind

1. Do you need to open a port for a service? Such as a custom port 5555 for apache service?
2. Do you mean the port is already listening but blocked by firewall so you want to open a port in firewall?
3. Open a port for custom temporary task such as transfer and receive files using this port and then close the port.

We will cover all these scenarios in this article

Check port status

To check the list of existing ports which are open we will use nmap to check port status:

Currently we see only two ports are open on my CentOS 8 node.

Check list of listening ports

We will use netstat to list the TCP ports which are in listening state. The total number of ports are higher compared to the nmap output.

Open a port for some service

If this is your requirement then you are looking for the wrong question. Basically it is other way round i.e. a service will open a port. For example when you start SSHD service, by default it will start port 22 and not the other way round i.e. if you open port 22, it will not automatically start SSHD service.

Let us observe this in example, we know that port 22 is open on my CentOS 8 node. If I stop the sshd service

You can see that port 22 is not open anymore.

You must use respective service’s configuration file to change the default port. Once done you can restart the service and that should automatically open the respective port on your Linux node.

This covers the first scenario.

firewalld open port

It is also possible that your ports are disabled in firewall. If your port is not listed in nmap then it is most likely blocked by firewall.

We will use firewalld to open a port as this is the most used interface today in RHEL/CentOS 7 and 8. Determine which zone the system’s network interfaces are in. In the following example, the eth0 and eth1 interface is in the ‘public’ zone:

To permanently firewalld open port in a zone use the —add-port option. The example below permanently opens TCP port 1234 in the ‘public‘ zone. Note that permanent changes do not take effect until the firewalld service is reloaded.

Once firewalld open port, next use netstat to check port status:

We still don’t see port 1234 here. This is because currently port 1234 is not bind to any service . So our port is OPEN but NOT LISTENING. As soon as a request or service tries to use port 1234, we will get this in LISTEN state.

Use nc or ncat to open a port in Linux

Let us verify this theory Use nc or ncat to open a port in Linux nc or ncat is delivered as part of nmap-ncat rpm in RHEL/CentOS which you can install using yum or dnf. Use —listen with —port to open a port using nc command. In the below example we open port 1234

Open another terminal of this server and check port status

As you see port 1234 is listening for both IPv4 and IPv6. To only use IPv4 use -4 with the above command

Next on another terminal you can check port status for port 1234

Use nc or ncat to open a port and transfer files

We can also use nc to transfer file from one host to another host. Here I will transfer my » inputfile » from centos-8 to rhel-8 On the client we will open a random port, here we will use 9899. I have enabled verbose so you can see more details on the screen

Next to start the transfer, use the below command

If you face any issues you can check the firewall between your server and client. It is possible that the respective port is blocked and you must use firewalld open port

Lastly I hope the steps from the article to open a port and check port status on Linux was helpful. So, let me know your suggestions and feedback using the comment section.

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3 thoughts on “Easy steps to open a port in Linux RHEL/CentOS 7/8”

A very thorough and helpful post. I was trying to allow ssh on a secondary port and could not get it to work using the usual advice (w/CentOS8.)
The recommendation you provided to add the port using the firewall-cmd was the missing ingredient:

Thanks for this!

Hi
I did below steps and reloaded firewall but still when I do netstat -ntlp port 1234 not showing open

I did explained this part in the article

We still don’t see port 1234 here. This is because currently port 1234 is not bind to any service. So our port is OPEN but NOT LISTENING. As soon as a request or service tries to use port 1234, we will get this in LISTEN state.

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