Sorry in advance for such a noob question, but I'm certainly a noob.
My question is what does it mean to LISTEN or ACCEPT on a port as it relates to my example?
EXAMPLE:
I have a tomcat server, and It will use port 8080. I want to make sure that port is available for me to use.
What commands should I perform on my unix server and why?
what information would a command like this give me: netstat -an | grep LISTEN
If a port shows up as LISTEN in netstat, it means the port is in use by a server process, so you can't use it. Here is an example:
tcp 0 0 127.0.0.1:631 0.0.0.0:* LISTEN
which shows that port 631 is in use.
Ignore the UNIX type sockets at the end - they are irrelevant.
For checking port 8080 is in use or not, you can simply use the command netstat -an|grep 8080. If you get an output in below format, that means 8080 is already in use and you need to assign a new port for the tomcat.
# netstat -an
tcp 0 0 127.0.0.1:8080 0.0.0.0:* LISTEN
Netstat command displays various network related information such as network connections, routing tables, interface statistics, masquerade connections, multicast memberships etc,
a option with netstat will give you both listening and non listening ports
n option when you don’t want the name of the host, port or user to be displayed, use netstat -n option. This will display in numbers, instead of resolving the host name, port name, user name. This also speeds up the output, as netstat is not performing any look-up.
For more understand the use of netstat command here are its options:
-a : All ports
-t : Ports TCP
-u : Ports UDP
-l : Listening ports
-n : IP address without domain name resolution
-p : Name of the program and it associated PID
So:
-To display all port (TCP & UDP), PId with the associated name of the program :
$ netstat -paunt
-To display all Listening ports (TCP), PId with the associated name of the program : (and we can also filter with the grep command)
$ sudo netstat -plnt | grep ':80'
I hope it will be helpful :)
You can also use telnet to check if the port is open and listening e.g,
Zeeshan$ telnet google.com 80
Trying 173.194.35.5...
Connected to google.com.
Escape character is '^]'.
I am telnetting google.com on port 80. If you see the third line in the output, you will notice it says it is connected with the Google's web server. The same way you have a JAVA application server called Tomcat and it is listening on port 8080. In fact it is asking clients to connect to it on port 8080 so it can give away the JAVA services to client. When I will use from a client side telnet localhost 8080 I will be connected the same way I have connected with Google's web server on port 80. Provided that Tomcat is running and listening on port 8080. If port 8080 is not free and occupied by some other application you can simply change the port 8080 to another free port. Telnet should give you the following status:
accepted (connected), refused, and timeout
connection refused - nothing is running on that port
accepted - some application is running on the port
timeout - a firewall is blocking access
So now there are two possible ways to check. From the same machine you are running Tomcat server:
telnet localhost 8080
Of if you want to check it from some other machine or outside of the network:
telnet 192.168.1.1 8080
I hope that helps.
use can also run the below command, it will list the Port and corresponding PID, if any process is using those ports
netstat -tulpn
Related
How can I use the port 80 on my local Linux machine as the port of my node server?
The netstat command netstat -ptuln says the following about this port, while the node server is running:
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 127.0.0.1:80 0.0.0.0:* LISTEN -
I found on this site some recommendations for the command sudo iptables -I INPUT -p tcp -m tcp --dport 80 -j ACCEPT. I executed this command but when I make a request with curl (curl 1.97.xxx.xxx.xx) it keeps responding with curl: (7) Failed to connect to xxxxxx port 80: Connection refused.
But using curl the following ways works: curl 0.0.0.0:80 or curl localhost:80.
My conclusion is, that I somehow have not opened the port correctly, but all I could find on the internet repetitively is the command I mentioned earlier.
I am aware of the fact that I could fix this easily by using an apache server, but I would like to make it without it.
Thank you!
Paste the output from
netstat -ptuln
command.I think the problem is that your web server runs on local address and can not be reachable for other machines in network.
When I'm trying to run a service (RavenDB) on port 8080 it stops and the Windows Logs show the following error:
System.Reflection.TargetInvocationException: Exception has been thrown by the target of an invocation. ---> System.Net.HttpListenerException: Failed to listen on prefix 'http://+:8080/' because it conflicts with an existing registration on the machine.
Acccording to IIS and netstat -an | find "8080" the port is currently not in use.
If I change the port to any other, the problem disappears.
Port 8080 may actually be in use. To replicate another answer
netstat -a only lists connected sockets and listening socket.
-a Displays all connections and listening ports. Neither
connect nor listen was called on your socket, so it falls outside the
purview of netstat -a.
However, since Windows 10, you can use netstat -q.
-q Displays all connections, listening ports, and bound
You could also try to view the port using tcpview from the SysInternals suite. Sort by port number. It will also tell you the process using the port, which you can then kill.
I set my linux as an access point, and then run simple web-server that print "hello world" at port 3000.
and connect it with my smart phone successfully.
in linux terminal, http://localhost:3000 works well.
But in smart phone,
If I access to http://172.24.1.105:3000, can't connect to it. (172.24... is ap's ip)
the chrome's error message is
This site can't be reached. 172.24.1.105 refused to connect
I searched Google (https://serverfault.com/questions/725262/what-causes-the-connection-refused-message) and I suspicious linux's firewall.
pi#raspberrypi:~/prj/ap_server $ sudo tcpdump -n icmp
listening on eth0, link-type EN10MB (Ethernet), capture size 262144 bytes
... when I access to port 3000,
15:07:13.102750 IP 192.168.0.3 > 168.126.63.2: ICMP 192.168.0.3 udp port 42531 unreachable, length 386
the log is above. so I couldn't reach ap's webserver.
so I wonder two things...
1. How can I disable to its port block?
2. in tcpdump log, I access to port 3000 actually, why the log print port 42531?
Plus)
even I type sudo service iptables stop, the problem is not solved
sudo netstat -ntlp | grep 3000 logs:
**tcp6 0 0 :::3000 :::* LISTEN 1999/nodejs**
+I followed this tutorial-> https://frillip.com/using-your-raspberry-pi-3-as-a-wifi-access-point-with-hostapd/ .
and there is ipv4 setting.
If you want to run it on your mobile it will work on Live IP (externel) address
if it is working fine on local address (localhost) and not on live IP then
enable routing from your router
and allow that specific port it will work fine.
I found the issue.
my dhcp set was
interface=wlan0 # Use interface wlan0
listen-address=172.24.1.1 # Explicitly specify the address to listen on
bind-interfaces # Bind to the interface to make sure we aren't sending things elsewhere
server=8.8.8.8 # Forward DNS requests to Google DNS
domain-needed # Don't forward short names
bogus-priv # Never forward addresses in the non-routed address spaces.
dhcp-range=172.24.1.50,172.24.1.150,12h # Assign IP addresses between 172.24.1.50 and 172.24.1.150 with a 12 hour lease time
like above.
I tried to connect the external ip(172.24.1.105) that I can see on mobile continuously but got failed. but when I tried with 172.24.1.1, then success.
I don't know why. maybe there is accurate ip address and something in mobile is temporal.
See similar topic at Node JS not listening to port 1337 on server
Your web server is not listening remote address.
I have shut down iptables for my server, inspite of that when I check on http://www.yougetsignal.com/tools/open-ports/ it says my ports are not open.
Where do I have to specify to open ports. I am running a linux server
Is your server/PC behind a NAT router? If so, you may need to port forward the required ports to your server/PC. A helpful website for guides on how to do so (as it depends on your router model) is http://portforward.com/
If your server is not behind a NAT router or if you've verified you're port forwarding, is the application that's supposed to be listening on the specific port even running? Try this:
netstat -anp | grep <port number>
Netstat manual page: http://linux.die.net/man/8/netstat
If you can't find the port as listening on netstat, make sure that the application is running.
You need a server program (daemon) running on a machine listening on a port for that port to be open.
Setup the 'nmap' package on your server with 'yum install nmap -y' and check listening ports on your server:
nmap localhost
If you can see your port listening then you need to check your router for proper port forwarding, else you need to make sure that your application is working and listening for the port.
For the example, Apache2 will listen for port 80 by default.
My laptop is running a local neo4j server. I can use it with localhost:7474 but when i try connecting it with 192.168.1.12:7474 it is unreacheable.
Turns out linux is blocking connections other than web server port 80. Because i can access my Apache server on 192.168.1.12/
I am trying to allow TCP connections on port 7474 by using
iptables -A TCP -p tcp --dport 7474 -j ACCEPT
but it gives a response as -
iptables: No chain/target/match by that name.
How can i make other clients access neo4j server running at my laptop on port 7474. My laptop IP addr is 192.168.1.12.
I doubt that it is blocking it. Probably your neo4j server is only running at 127.0.0.1. You can check this out with netstat -nplt: you will probably see something (the apache) listening on 0.0.0.0:80 or :::80 (e.g. catchall address) but on port 7474 you will probably only see 127.0.0.1:7474 or ::1:7474. If this is the case you need to reconfigure your neo4j server to listen not only on localhost (don't know how, checkout the documentation).
Okay. I had uncommented the webserver address line but it still wasn't working.
So i reinstalled neo4j. That solved it. Weird but worked.