java.net.UnknownHostException: Invalid hostname for server: local - java

What are the steps I should take to solve the error:
java.net.UnknownHostException: Invalid hostname for server: local
I added the new virtual host name at Android emulator but the result returns to
java.net.UnknownHostException virtualhostname at
java.net.InetAddress.lookUpHostByName(InetAddress.java:506)
When I type my virtualhost URL on my PC, it works on display. Then again, when I ran on Emulator and check on Logcat, I couldn't be able to read or check the HTTP status if 200, 202, or an error code number. It simply returned to UnknownHostException


I was having the same issue on my mac. I found the issue when I pinged my $HOSTNAME from terminal and it returned ping: cannot resolve myHostName: Unknown host.
To resolve:
Do echo $HOSTNAME on your terminal.
Whatever hostname it shows (lets say myHostName), try to ping it : ping myHostName. If it returns ping: cannot resolve myHostName: Unknown host then add an entry into your /etc/hosts file.
For that edit /etc/hosts file and add following:
127.0.0.1 myHostName


What the exception is really saying is that there is no known server with the name "local". My guess is that you're trying to connect to your local computer. Try with the hostname "localhost" instead, or perhaps 127.0.0.1 or ::1 (the last one is IPv6).
From the javadocs:
Thrown to indicate that the IP address
of a host could not be determined.
127.0.0.1or ::1 or "localhost" should always be the loopback interface, so if that doesn't work I'd be really surprised.
If there really is a server called "local" on your network - examine your DNS settings or add it to your hosts file.


java.net.UnknownHostException: Host is unresolved:
Thrown to indicate that the IP address of a host could not be determined.
This exception is also raised when you are connected to a valid wifi but router does not receive the internet. Its very easy to reproduce this:
Connect to a valid wifi
Now remove the cable from the router while router is pluged-in
You will observe this error!!
You can't really solve this, You can only notify the user gracefully. (something like - "Unable to make a connection")


This is not specific to the question, but this question showed up when I was Googling for the mentioned UnknownHostException, and the fix is not found anywhere else so I thought I'd add an answer here.
The exception that was continuously received was:
java.net.UnknownHostException: google.com
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:184)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:392)
at java.net.Socket.connect(Socket.java:589)
at java.net.Socket.connect(Socket.java:538)
at java.net.Socket.<init>(Socket.java:434)
at java.net.Socket.<init>(Socket.java:211)
...
No matter how I tried to connect to any valid host, printing it in the terminal would not help either. Everything was right.
The Solution
Not calling trim() for the host string which contained whitespace. In writing a proxy server the host was obtained from HTTP headers with the use of split(":") by semicolons for the HOST header. This left whitespace, and causes the UnknownHostException as a host with whitespace is not a valid host. Doing a host = host.trim() on the String host solved the ambiguous issue.


Your hostname is missing. JBoss uses this environment variable ($HOSTNAME) when it connects to the server.
[root#xyz ~]# echo $HOSTNAME
xyz
[root#xyz ~]# ping $HOSTNAME
ping: unknown host xyz
[root#xyz ~]# hostname -f
hostname: Unknown host
There are dozens of things that can cause this. Please comment if you discover a new reason.
For a hack until you can permanently resolve this issue on your server, you can add a line to the end of your /etc/hosts file:
127.0.0.1 xyz.xxx.xxx.edu xyz


This might happen due to various reasons
1) Check if you have VPN connected, you might get this error sometimes if yes
"Your hostname, localhost resolves to a loopback address: 127.0.0.1; using 10.xxx.1.193 instead (on interface cscotun0)"
2) Check your $HOSTNAME
3) try to ping $HOSTNAME on commandline and if it doesnt work, tweak the system settings to make your local host respond to pings


Try the following :
String url = "http://www.google.com/search?q=java";
URL urlObj = (URL)new URL(url.trim());
HttpURLConnection httpConn =
(HttpURLConnection)urlObj.openConnection();
httpConn.setRequestMethod("GET");
Integer rescode = httpConn.getResponseCode();
System.out.println(rescode);
Trim() the URL


Trying to connect to your local computer.try with the hostname "localhost" instead or perhaps ::/ - the last one is ipv6


Please try to set SPARK_LOCAL_IP environment variable to the ip address(can be localhost i.e. your own ip address) you want to connect. E.g.
$ export SPARK_LOCAL_IP=182.95.208.152
This way you will not be required to alter existing linux settings.
Worked for me, hope helps you too.


Connect your mobile with different wifi connection with different service provider.
I don't know the exact issue but i could not connect to server with a specific service provider but it work when i connected to other service provider. So try it!


I had this issue in my android app when grabbing an xml file the format of my link was not valid, I reformatted with the full url and it worked.


If you are here because your emulator gives you that Exception, Go to Tools > AVD Manager in your android emulator and Cold boot your Emulator.


I had the same issue.
Restart docker was the fix for me. For some reason it needed a restart, I don´t know why, but it worked.


If your /etc/localhosts file has entry as below:
Add hostname entry as below:
127.0.0.1 local host (add your hostname here)
::1 (add hostname here) (the last one is IPv6).
This should resolve the issue.

Related

java.net.SocketException: Unresolved address

I have implemented a server application in Java that I am trying to deploy in the cloud. I have a problem with this part of the code
serverSocket = ServerSocketChannel.open();
serverSocket.socket().bind(new InetSocketAddress(myHost,myPort));
When I set String myHost = "localhost", everything works fine. However, I would like to it to work with the public Ip of the remote machine. I have tried 2 different things
String myHost = "10.0.0.4" (the Ip I get when running ifconfig). In that case I get
java.net.BindException: Cannot assign requested address
at sun.nio.ch.Net.bind0(Native Method)
at sun.nio.ch.Net.bind(Net.java:433)
at sun.nio.ch.Net.bind(Net.java:425)
at sun.nio.ch.ServerSocketChannelImpl.bind(ServerSocketChannelImpl.java:223)
at sun.nio.ch.ServerSocketAdaptor.bind(ServerSocketAdaptor.java:74)
at sun.nio.ch.ServerSocketAdaptor.bind(ServerSocketAdaptor.java:67)
String myHost = "publichost", and I add a line 10.0.0.4 publichost to my /etc/hosts/ file. In that case I get
java.net.SocketException: Unresolved address
at sun.nio.ch.Net.translateToSocketException(Net.java:131)
at sun.nio.ch.Net.translateException(Net.java:157)
at sun.nio.ch.Net.translateException(Net.java:163)
at sun.nio.ch.ServerSocketAdaptor.bind(ServerSocketAdaptor.java:76)
at sun.nio.ch.ServerSocketAdaptor.bind(ServerSocketAdaptor.java:67)
What I am doing wrong?

The first error (typically) means that you are binding to an IP + port combination that is already in use.
Use netstat -lntp to list all of the programs listening on a tcp port, and look for the port you are trying to use. Then either shutdown the program ... or pick a different port.
It might also mean that you are using the wrong IP entirely. When you call bind on a server socket, the address and port should be the IP and port on which your application expects to receive incoming connections. So the IP must be an IP for this host (NOT the remote host). Note that you can also use 0.0.0.0 ... which means "all IP addresses for this host".
The second error could mean:
Your DNS resolver is not looking at your "/etc/hosts" file.
The /etc/hosts entry is incorrect; you are supposed to put the fully qualified name for your host into the entry; see Fully qualified machine name Java with /etc/hosts
Something else.
But I suspect that if you fixed the "Unresolved address" problem without fixing the cause of the original "Cannot assign requested address", the latter would reappear. You shouldn't need a DNS entry to bind a server socket!

Java RMI 'java.rmi.ConnectException: Connection refused to host: 127.0.1.1;' [duplicate]

java.rmi.ConnectException: Connection refused to host: 127.0.1.1; nested exception is:
java.net.ConnectException: Connection refused
at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEndpoint.java:619)
at sun.rmi.transport.tcp.TCPChannel.createConnection(TCPChannel.java:216)
at sun.rmi.transport.tcp.TCPChannel.newConnection(TCPChannel.java:202)
at sun.rmi.server.UnicastRef.invoke(UnicastRef.java:128)
at java.rmi.server.RemoteObjectInvocationHandler.invokeRemoteMethod(RemoteObjectInvocationHandler.java:194)
at java.rmi.server.RemoteObjectInvocationHandler.invoke(RemoteObjectInvocationHandler.java:148)
at com.sun.proxy.$Proxy0.notifyMe(Unknown Source)
at CallbackServerImpl.doCallback(CallbackServerImpl.java:149)
at CallbackServerImpl.registerForCallback(CallbackServerImpl.java:70)
at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:57)
at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
at java.lang.reflect.Method.invoke(Method.java:601)
at sun.rmi.server.UnicastServerRef.dispatch(UnicastServerRef.java:322)
at sun.rmi.transport.Transport$1.run(Transport.java:177)
at sun.rmi.transport.Transport$1.run(Transport.java:174)
at java.security.AccessController.doPrivileged(Native Method)
at sun.rmi.transport.Transport.serviceCall(Transport.java:173)
at sun.rmi.transport.tcp.TCPTransport.handleMessages(TCPTransport.java:553)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run0(TCPTransport.java:808)
at sun.rmi.transport.tcp.TCPTransport$ConnectionHandler.run(TCPTransport.java:667)
at java.util.concurrent.ThreadPoolExecutor.runWorker(ThreadPoolExecutor.java:1145)
at java.util.concurrent.ThreadPoolExecutor$Worker.run(ThreadPoolExecutor.java:615)
at java.lang.Thread.run(Thread.java:722)
Caused by: java.net.ConnectException: Connection refused
at java.net.PlainSocketImpl.socketConnect(Native Method)
at java.net.AbstractPlainSocketImpl.doConnect(AbstractPlainSocketImpl.java:339)
at java.net.AbstractPlainSocketImpl.connectToAddress(AbstractPlainSocketImpl.java:200)
at java.net.AbstractPlainSocketImpl.connect(AbstractPlainSocketImpl.java:182)
at java.net.SocksSocketImpl.connect(SocksSocketImpl.java:391)
at java.net.Socket.connect(Socket.java:579)
at java.net.Socket.connect(Socket.java:528)
at java.net.Socket.<init>(Socket.java:425)
at java.net.Socket.<init>(Socket.java:208)
at sun.rmi.transport.proxy.RMIDirectSocketFactory.createSocket(RMIDirectSocketFactory.java:40)
at sun.rmi.transport.proxy.RMIMasterSocketFactory.createSocket(RMIMasterSocketFactory.java:146)
at sun.rmi.transport.tcp.TCPEndpoint.newSocket(TCPEndpoint.java:613)
... 23 more
I get this exception when I try to connect a remote client to my server. In both, server and client the hostName for the registryUrl of rmi is the public IP address of the server. I also tried to put localhost in server but the error doesn't change.
My java.policy is set to grant all connections to all ports and I have no firewalls enabled in the server or the client.
Any suggestions what could be?

This is item A.1 in the RMI FAQ. You need to either fix your /etc/hosts file or set the java.rmi.server.hostname property at the server.

PROBLEM SOLVED
I had exactly the same error. When the remote object got binded to the rmiregistry it was attached with the loopback IP Address which will obviously fail if you try to invoke a method from a remote address. In order to fix this we need to set the java.rmi.server.hostname property to the IP address where other devices can reach your rmiregistry over the network. It doesn't work when you try to set the parameter through the JVM. It worked for me just by adding the following line to my code just before binding the object to the rmiregistry:
System.setProperty("java.rmi.server.hostname","192.168.1.2");
In this case the IP address on the local network of the PC binding the remote object on the RMI Registry is 192.168.1.2.

you can use LocateRegistry such as:
Registry rgsty = LocateRegistry.createRegistry(1888);
rgsty.rebind("hello", hello);

I found many of the Q&A on this topic, not nothing was helping me - that's because my issue was more basic ( what can I say I am not a networking guru :) ). My ip address in /etc/hosts was incorrect. What I had tried included the following for CATALINA_OPTS:
CATALINA_OPTS="$CATALINA_OPTS -Djava.awt.headless=true -Xmx128M -server
-Dcom.sun.management.jmxremote
-Dcom.sun.management.jmxremote.port=7091
-Dcom.sun.management.jmxremote.authenticate=false
-Dcom.sun.management.jmxremote.ssl=false
-Djava.rmi.server.hostname=A.B.C.D" #howeverI put the wrong ip here!
export CATALINA_OPTS
My problem was that I had changed my ip address many months ago, but never updated my /etc/hosts file. it seems that by default the jconsole uses the hostname -i ip address in some fashion even though I was viewing local processes. The best solution was to simply change the /etc/hosts file.
The other solution which can work is to get your correct ip address from /sbin/ifconfig and use that ip address when specifying the ip address in, for example, a catalina.sh script:
-Djava.rmi.server.hostname=A.B.C.D

If you're running in a Linux environment, open the file /etc/hosts.allow
add the following line
ALL
Wildcards
Also check the /etc/hostname and /etc/host to see if there might be something wrong there.
I had to change my / etc / host from
127.0.0.1 localhost
127.0.1.1 AMK
to
127.0.0.1 localhost
127.0.0.1 AMK
also wrote in ALL in the file /etc/hosts.allow which was previously completely empty
Now everything works
do not know how safe it is. you have to read more about possible options for /etc/hosts.allow to do something that requires a touch of security.

Maybe your rmiregistry not be created before client trying connect to your server and it would lead to this exception.In Linux, you can use "netstat" to check your rmiregistry be bond on the right port you assigned in java code.

If you've tried modifying etc/hosts and adding java.rmi.server.hostname property as well but still registry is being bind to 127.0.0.1
the issue for me was resolved after explicitly setting System property through code though the same property wasn't picked from jvm args

It works for me after getting rid of "::1" in /etc/hosts.

I had the same exact problem and my issue was that I had 2 IP addresses from 2 different networks configured in the etc/hosts as below.
10.xxx.x.xxx localhost
192.xxx.x.xxx localhost
This should be because there was a conflict as to which IP to be used for the other devices to reach the rmiregistry over the network.
Once I removed the extra-record that is not required, I was able to solve the issue.
So my etc/hosts file had only the following record.
10.xxx.x.xxx localhost

In my case I was unable to edit the hosts file because using a pc from the university.
I fixed the problem running rmiregistry in another port (instead of 1099) with:
rmiregistry <port>
and then running the server on that port.
It was basically an error caused by occupied port.

when you want to connect to remote server with RMI you must add a system property same as:
System.setProperty("java.rmi.server.hostname","Ip or DNS of the server");
or add environment variable.
For me I got Connection Refused and solve it by adding this line of code in server side:
java -jar -Djava.rmi.server.hostname="ip or dns of the server" packageName.jar
Thank to other guy for guide me to solve it.

On Windows make sure your Windows firewall is correctly configure / disabled. I had to disable the Windows firewall (because I didn't bother with configuring it) to get things to work even when I was testing with localhost.

When I got the same error on my machine ("connection is refused"), the reason was that I had defined the following on the server side:
Naming.rebind("rmi://localhost:8080/AddService"
,addService);
Thus the server binds both the IP = 127.0.0.1 and the port 8080.
But on the client side I had used:
AddServerInterface st = (AddServerInterface)Naming.lookup("rmi://localhost"
+"/AddService");
Thus I forgot to add the port number after the localhost, so I rewrote the above command and added the port number 8080 as follows:
AddServerInterface st = (AddServerInterface)Naming.lookup("rmi://localhost:8080"
+"/AddService");
and everything worked fine.

You can simply use:
on server side:
Registry <objectName1> = LocateRegistry.createRegistry(1099);
Registry <objectName2> = LocateRegistry.getRegistry();
on Client Side:
Registry <object name you want> = LocateRegistry.getRegistry();

Localhost address in the Virtual Machine

I am using a virtual machine on a server.
My local IP of the VM is 192.168.1.10
I am trying to achieve something which requires me to edit my /etc/hosts as provided in this link
http://www.thatisjava.com/java-tech/55200/
I am having similar problems, My console reads
RTP--- :DataAddress: /192.168.1.10
ControlAddress: /192.168.1.10
DataPort: 42050
ControlPort: 42051
java.io.IOException: Local Data AddressDoes not belong to any of this hosts local interfaces
java.io.IOException: Local Data AddressDoes not belong to any of this hosts local interfaces
at org.speechforge.cairo.rtp.RTPConsumer.init(RTPConsumer.java:181)
at org.speechforge.cairo.rtp.RTPConsumer.<init>(RTPConsumer.java:95)
at org.speechforge.cairo.rtp.server.RTPStreamReplicator.<init> (RTPStreamReplicator.java:69)
And some more.
The answer to the problem given is
I solved this one. The problem is JMF seems to use
InetAddress.getAllByName() which returns (at least in my case) only
single IP address no matter how many addresses I have defined on my
interfaces. The problem was solved by placing my IP address that I
wanted to use by session manager into /etc/hosts. It must be the first
line in /etc/hosts otherwise the other row that matches is used.
Unfortunately, I cant make out what He is trying to state. My /etc/hosts read
127.0.0.1 localhost
127.0.1.1 SparkVM104
So am I supposed to change 127.0.0.1 with my 192.168.1.10
or am I supposed to create an alias like 127.0.0.1/192.168.1.10
or Shall I just paste 192.168.1.10 in the top as
192.168.1.10
127.0.0.1 localhost
127.0.1.1 SparkVM104
Any help is appreciated.
Regards.

The format for /etc/hosts is
IP_address canonical_hostname [aliases...]
(see http://linux.die.net/man/5/hosts), so to list 192.168.1.10 first, the /etc/hosts file would have to look like this:
192.168.1.10 SomeHostName SomeOtherHostName
127.0.0.1 localhost

In /etc/hosts, localhost should map to 127.0.0.1 and nothing else, and your external hostname to your external IP address and nothing else. Some Linux distributions are stated to violate this rule and it breaks everything.

Java Socket connection refused with my Public IP

I have a client server architecture project in android. I cant connect with my public IP to server. I closed firewall, and did the port redirection for server. My friend can connect from outside to my server, but i can't, why? how can it be?..
Thanks..

Which OS are you running your client server code. If Windows, look for c:\Windows\System32\drivers\etc\hosts, if it's linux go the /etc/hosts/ file
Open the file with sudo privileges.
Format:
<IP> <HOSTNAME>.<DOMAIN> <ALIAS>
Example:
127.0.0.1 localhost.localdomain localhost
Add your IP here with domain name. Your Domain Name can be anything and try again. Also your question is a bit vague. Please add more details such as your os env and what exactly are you trying to achieve?

UnknkownHostException

Please help;
Am trying to deploy a web application.
The build is returning successful,and am not getting any errors on the sever.log
however am getting a http 503 error:the requested service() is not currently available
and also my
Java DB Database Process has this message
Warning: UnknkownHostException: intracare: intracare.
Could not listen on port 1527 on host localhost.
am using glassfish v3 prelude

Possibly you already have another application (perhaps another JavaDB instance?) listening on port 1527 - that could explain the "could not listen" message. Use netstat to check.

I think that UnknownHostException is related that intracare can't be resolved to an IP.
I would:
Ping that host.
Check C:\WINDOWS\system32\drivers\etc\hosts or /etc/hosts files.
Regards.

Check the DNS settings on the host. Your short names do not resolve correctly.

Mayby string you are typing as a host name is wrong? Maybe it is firewall problem?

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