Hadoop job tracker only accessible from localhost

I'm setting up Hadoop (0.20.2). For starters, I just want it to run on a single machine - I'll probably need a cluster at some point, but I'll worry about that when I get there. I got it to the point where my client code can connect to the job tracker and start jobs, but there's one problem: the job tracker is only accessible from the same machine that it's running on. I actually did a port scan with nmap, and it shows port 9001 open when scanning f开发者_StackOverflowrom the Hadoop machine, and closed when it's from somewhere else.

I tried this on three machines (one Mac, one Ubuntu, and an Ubuntu VM running in VirtualBox), it's the same. None of them have any firewalls set up, so I'm pretty sure it's a Hadoop problem. Any suggestions?

In your hadoop configuration files, does fs.default.name and mapred.job.tracker refer to localhost?

If so, then Hadoop will only listen to port 9000 and 9001 on the loopback interface, which is inaccessible from any other host. Make sure fs.default.name and mapred.job.tracker refer to your machine's externally accessible host name.

Make sure that you have not double listed your master in the /etc/hosts file. I had the following which only allowed master to listen on 127.0.1.1

127.0.1.1    hostname    master
192.168.x.x  hostname    master
192.168.x.x  slave-1
192.168.x.x  slave-2

The above answer caused the problem. I changed my /ect/hosts file to the following to make it work.

127.0.1.1    hostname   
192.168.x.x  hostname    master
192.168.x.x  slave-1
192.168.x.x  slave-2

Use the command netstat -an | grep :9000 to verify your connections are working!

In addition to the above answer, I found that in /etc/hosts on the master (running ubuntu) had the line:

127.0.1.1 master

Which meant that running nslookup master on the master returned a local address - so in spite of using master in mapred-site.xml I suffered the same problem. My solution (there are probably better ones) was to create an alias in my DNS server and use that instead. I guess you could probably also change the IP address in /etc/hosts to the external one, but I haven't tried this - I'm not sure what implications it would have for other services.