Hadoop slave cannot connect to master, even when service is running and ports are open - hadoop

Question

I'm running hadoop 2.5.1 and I'm having a problem when slaves are connecting to master. My goal is to set-up a hadoop cluster. I hope someone can help, I'm been poundering with this too long already! :)
This is what comes up to the log file of slave:
2014-10-18 22:14:07,368 WARN org.apache.hadoop.hdfs.server.datanode.DataNode: Problem connecting to server: master/192.168.0.104:8020
This is my core-site.xml -file (same on master and slave):
<configuration>
<property>
<name>fs.default.name</name>
<value>hdfs://master/</value>
</property>
</configuration>
This is my hosts -file ((almost)same on master and slave).. I have hard coded addresses to there without any success:
127.0.0.1 localhost
192.168.0.104 xubuntu: xubuntu
192.168.0.104 master
192.168.0.194 slave
# The following lines are desirable for IPv6 capable hosts
::1 ip6-localhost ip6-loopback
fe00::0 ip6-localnet
ff00::0 ip6-mcastprefix
ff02::1 ip6-allnodes
ff02::2 ip6-allrouters
Netstats from master:
xubuntu#xubuntu:/usr/local/hadoop/logs$ netstat -atnp | grep 8020
(Not all processes could be identified, non-owned process info
will not be shown, you would have to be root to see it all.)
tcp 0 0 192.168.0.104:8020 0.0.0.0:* LISTEN 26917/java
tcp 0 0 192.168.0.104:52114 192.168.0.104:8020 ESTABLISHED 27046/java
tcp 0 0 192.168.0.104:8020 192.168.0.104:52114 ESTABLISHED 26917/java
Nmap from master to master:
Starting Nmap 6.40 ( http://nmap.org ) at 2014-10-18 22:36 EEST
Nmap scan report for master (192.168.0.104)
Host is up (0.000072s latency).
rDNS record for 192.168.0.104: xubuntu:
PORT STATE SERVICE
8020/tcp open unknown
..and nmap from slave to master (even when the port is open, the slave doesn't connect to it..):
ubuntu#ubuntu:/usr/local/hadoop/logs$ nmap master -p 8020
Starting Nmap 6.40 ( http://nmap.org ) at 2014-10-18 22:35 EEST
Nmap scan report for master (192.168.0.104)
Host is up (0.14s latency).
PORT STATE SERVICE
8020/tcp open unknown
What is this all about? The problem is not about firewall.. I have also read every thread there is to to this without any success. I'm frustrated to this.. :(

Answer 1

At least one of your problems is that you are using old configuration name for the HDFS. For version 2.5.1 the configuration name should be fs.defaultFS instead of fs.default.name. I also suggest defining the port in the value, so the value would be hdfs://master:8020.
Sorry, I'm not linux guru, so I don't know about nmap, but does telnet'ing work from slave to master to the port?