I'm developing a Qt application and experience rather weird network issue.
Let me show how it looks from end-user perspective.
First I start up my server and verify that it's listening on a target port:
[user#host server]$ sudo netstat -anp | grep 30004
tcp 0 0 0.0.0.0:30004 0.0.0.0:* LISTEN 11113/./server
Then I connect to the server with telnet:
[user#host server]$ telnet localhost 30004
Trying ::1...
telnet: connect to address ::1: Connection refused
Trying 127.0.0.1...
Connected to localhost.
Escape character is '^]'.
Connection closed by foreign host.
Netstat displays that connection is now established. Nothing fancy so far:
[user#host server]$ sudo netstat -anp | grep 30004
tcp 0 0 0.0.0.0:30004 0.0.0.0:* LISTEN 11113/./server
tcp 0 0 127.0.0.1:30004 127.0.0.1:34608 ESTABLISHED 11113/./server
tcp 0 0 127.0.0.1:34608 127.0.0.1:30004 ESTABLISHED 12657/telnet
Then the server drops the connection based on application-specific timeout. It is set to 10 seconds at the moment:
[user#host server]$ sudo netstat -anp | grep 30004
tcp 0 0 0.0.0.0:30004 0.0.0.0:* LISTEN 11113/./server
tcp 0 0 127.0.0.1:30004 127.0.0.1:34608 TIME_WAIT -
I then shut down the server and verify that the listenning socket is destroyed:
[user#host server]$ sudo netstat -anp | grep 30004
tcp 0 0 127.0.0.1:30004 127.0.0.1:34608 TIME_WAIT -
Finally I start up the server again, but the listening port doesn't show up anymore:
[user#host server]$ sudo netstat -anp | grep 30004
tcp 0 0 127.0.0.1:30004 127.0.0.1:34608 TIME_WAIT -
As a result client cannot connect to the server:
[user#host server]$ telnet localhost 30004
Trying ::1...
telnet: connect to address ::1: Connection refused
Trying 127.0.0.1...
telnet: connect to address 127.0.0.1: Connection refused
What am I doing wrong here? I'm inclined to think that this is a configuration issue, not a bug in the application.
This scenario seems to work on my laptop's Ubuntu. The aforementioned output was produced on linux box as well.
UPDATE: One more thing that is different in these two environemnt is qt version. On my notebook I have 4.8.6, on linux box it's 4.6.2. Not sure if it matters.
Apparently there was an issue with versions of qt libraries. We upgraded it to latest 4.x.x and now the problem seems to be resolved.
Related
Mongo up and running on CentOs Machine
All IPs enabled, no authorization
# network interfaces
net:
port: 27017
bindIp: 0.0.0.0
# security: none
# authorization: 'enabled
Port enabled
netstat -tulnp
(No info could be read for "-p": geteuid()=1001 but you should be root.)
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:27017 0.0.0.0:* LISTEN -
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN -
tcp 0 0 127.0.0.1:5432 0.0.0.0:* LISTEN -
Connection from the server itself using the IP works fine
mongo --host 10.X.X.16
MongoDB shell version v4.2.2
connecting to: mongodb://10.X.X.16:27017/?compressors=disabled&gssapiServiceName=mongodb
MongoDB server version: 4.2.2
Server has startup warnings:
2020-01-21T15:48:26.297-0800 I CONTROL [initandlisten]
Doing the same thing from a remote Windows Machine
mongo --host 10.X.X.16
MongoDB shell version v4.2.1
connecting to: mongodb://10.X.X.16:27017/?compressors=disabled&gssapiServiceName=mongodb
2020-01-21T15:59:07.563-0800 E QUERY [js] Error: couldn't connect to server 10.65.5.16:27017, connection attempt failed: NetworkTimeout: Error connecting to 10.X.X.16:27017 :: caused by :: Socket operation timed out :
connect#src/mongo/shell/mongo.js:341:17
#(connect):2:6
2020-01-21T15:59:07.571-0800 F - [main] exception: connect failed
2020-01-21T15:59:07.571-0800 E - [main] exiting with code 1
Thanks!
Problem fixed:
I had to disable the firewall for the mongo port
sudo firewall-cmd --zone=public --add-port=27017/tcp --permanent
sudo firewall-cmd --reload
Node Exporter is always running on my local machine on localhost:9100 even if I don't execute it with terminal following this error message:
FATA[0000] listen tcp :9100: bind: address already in use source="node_exporter.go:172"
By which I can understand that this port number is already being used by another application but the thing is I don't have anything hosted there.
This is what netstat | grep 9100 gives:
tcp 0 0 localhost:60232 localhost:9100 ESTABLISHED
tcp6 0 0 localhost:9100 localhost:60232 ESTABLISHED
All I had to do was to "kill" the 9100 port in which Node Exporter was running by using fuser -k 9100/tcp as this was shown on How to kill a process running on particular port in Linux?.
I created a CentOS on GCE and installed dsc-cassandra 3.0. Then I changed the rpc_address from localhost to the internal ip or external ip in cassandra.yaml.
On the VM, I started cassandra and use cqlsh to access cassandra successfully. But I couldn't use cqlsh internal_ip or cqlsh external_ip.
Also, I turned on tcp:9042 port for this instance.
But I still couldn't access Cassandra from my local java app with the NoHostAvailableException(Cannot connect).
By the way, I did the same thing of my local VM running with VM VistualBox. I could access it.
Running sudo netstat -lntp | grep pid displayed:
tcp 0 0 127.0.0.1:33743 0.0.0.0:* LISTEN 1207/java
tcp 0 0 127.0.0.1:7000 0.0.0.0:* LISTEN 1207/java
tcp 0 0 127.0.0.1:7199 0.0.0.0:* LISTEN 1207/java
tcp6 0 0 127.0.0.1:9042 :::* LISTEN 1207/java
The Ip address was still 127.0.0.1. I think this is the problem.
How to configure the cassandra.yaml file?
I know where I was wrong.
I used sudo service cassandra restart to restart cassandra after editing the cassandra.yaml. The terminal showed:
Restarting cassandra (via systemctl): [ OK ]
Actually, I think it didn't really restart it. Then I used nodetool stopdaemon to stop cassandra and then start it again. The configuration of cassandra.yaml worked.
Helpful commands:
1.
ps aux | grep cassandra
sudo netstat -lntp | grep <cassandra_pid>
Using these commands to verify the ip/port of the cassandra service on remote VM.
tcp 0 0 127.0.0.1:7000 0.0.0.0:* LISTEN 5928/java
tcp 0 0 127.0.0.1:42682 0.0.0.0:* LISTEN 5928/java
tcp 0 0 127.0.0.1:7199 0.0.0.0:* LISTEN 5928/java
tcp6 0 0 10.138.0.2:9042 :::* LISTEN 5928/java
2.
telnet <cassandra_ip> 9042
Using this command to verify the ip/port of the cassandra service on local machine.
I have a:
Rasberry Pi 2
running
Raspbian Jessie Version:November 2015
I am using Undertow (a Java http server) to serve a website. This is the code that I use to build the server.
Undertow server = Undertow.builder()
.addHttpListener(8890, "localhost")
.setHandler(Handlers.pathTemplate()
.add("/", resource(new PathResourceManager(staticFilePath, 100))
.setDirectoryListingEnabled(false))
.build();
Problem: I am unable to see the webserver from another machine on the local network despite being able to ping and SSH into the PI.
What I have done (on the Pi2):
wget localhost:8890
returns the index.html correctly
netstat -lptn
Active Internet connections (only servers)
Proto Recv-Q Send-Q Local Address Foreign Address State PID/Program name
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN -
tcp6 0 0 :::22 :::* LISTEN -
tcp6 0 0 127.0.0.1:8890 :::* LISTEN 1743/java
Chrome on my development machine 192.168.1.8:8890 gives
ERR_CONNECTION_REFUSED
wget 192.168.1.8:8890
Connecting to 192.168.1.8:8890... failed: Connection refused.
nmap 192.168.1.8
Starting Nmap 6.40 ( http://nmap.org ) at 2015-12-05 14:05 CST
Nmap scan report for 192.168.1.8
Host is up (0.039s latency).
Not shown: 999 closed ports
PORT STATE SERVICE
22/tcp open ssh
Nmap done: 1 IP address (1 host up) scanned in 1.83 seconds
It is my understanding that there is no firewall so I am baffled as to why I can't see the server from my development machine.
See:
tcp6 0 0 127.0.0.1:8890 :::* LISTEN 1743/java
Your web server listens only on localhost address (127.0.0.1). This way it couldn't be accessed from anywhere but localhost.
And your nmap scan shows the same: the only remotely accessible port is 22.
To access this service remotely you have to bind web server to any non-local address belonging to this raspberry pi (192.168.1.8) or to "any address" 0.0.0.0, as SSH service is bound.
How to do this is written in the manual of your web server. Probably, you have to start is with a "-d" param, i.e.
standalone.sh -b=0.0.0.0
standalone.sh -Djboss.bind.address=0.0.0.0
or something like this.
In listener setup code this looks like
"localhost" have to be replaced with some public name. This could be "0.0.0.0" or "192.168.1.8". We also can
cat "192.168.1.8 somename" >> /etc/hosts
and then use somename:
Undertow server = Undertow.builder() .addHttpListener(8890, "somename")
I have running centos on guest machine (using virtualbox, connection over nat).
And there's tomcat running on this machine on port 8080.
<Connector port="8080" protocol="HTTP/1.1" address="0.0.0.0"
connectionTimeout="20000"
redirectPort="8443" />
There's port forwarding from host to guest
host 2222, guest 22 (ssh)
host 40001, guest 8080
I try to get page from http://localhost:8080
If I connect from host via ssh and do curl localhost:8080 I get an html page.
But if try to get http://localhost:40001 via browser, it becomes infinitely loading.
netstat -an | find "40001" on host machine shows
C:\Users\user>netstat -an | find "40001"
TCP 0.0.0.0:40001 0.0.0.0:0 LISTENING
TCP 127.0.0.1:30279 127.0.0.1:40001 FIN_WAIT_2
TCP 127.0.0.1:40001 127.0.0.1:30279 CLOSE_WAIT
If I try to telnet on host machine (telnet localhost 40001) the connection is ok.
If I try to get a netstat on guest, I get this
[aegis#localhost ~]$ netstat -an | grep LISTEN | grep tcp
tcp 0 0 127.0.0.1:8005 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:8009 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:8080 0.0.0.0:* LISTEN
tcp 0 0 0.0.0.0:22 0.0.0.0:* LISTEN
tcp 0 0 127.0.0.1:25 0.0.0.0:* LISTEN
tcp6 0 0 :::22 :::* LISTEN
tcp6 0 0 ::1:25 :::* LISTEN
I can't figure out why telnet from host is working, but I can't get a page via browser. Could you help me, where I've made a mistake in configuration?
At first, I was discaraged because of working "telnet localhost 40001 from host machine".
But there's difference between 22 and 8080 ports.
22 port is opened by default.
8080 port is not.
If you'll have such a problem, you should allow the firewall connection over 8080 port.
E.g., you can execute this statement:
iptables -I INPUT 1 -i eth0 -p tcp --dport 8080 -j ACCEPT