How to Overcome "Nautilus cannot handle smb locations"

I recently meet a problem with Nautilus in accessing the Windows shares or Samba shares. Whenever I tried "smb://" in Nautilus, I received "Nautilus cannot handle "smb" locations". When I tried to use "Connect to Server" dialog, there was no option "Windows share" in Type field.

After looking at a series of posts on the Internet, I have found that it is the problem of GVFS without Samba support. Consequently, the solution on Fedora is very very simple, just install the gvfs-smb package.

# yum install gvfs-smb

Actually, the most time-consuming part is the problem caused by myself, perhaps. There is some conflict between samba4 and samba (3) on my Fedora 17. The _local repository contains libwbclient v4 which is conflict with gvfs-smb which uses libwbclient v3. It takes very long  time to recognize the reason and to solve it. If you meet the same problem on new Fedoras (16, 17) and cannot solve it, please leave a comment here.

Setting up RSH on RHEL/CentOS

Although SSH dominates on remote control of Linux/Unix system because of its secure, RSH still has dedicated area to work such as in the internal network of a cluster, for example. However, setting up RSH server is not as trivial as SSH server. It takes some little effort for working properly.

At first step, install RSH server using yum as usual. Do it on every machines.

# yum install rsh-server rsh

RSH service is put under xinetd service, and it is disabled by default. To enable rsh service, open file /etc/xinetd.d/rsh and change "yes" to "no" at the line "disabled".

sed -i "s/^\(.*disable.*=.*\)yes\(.*\)$/\1no\2/g" /etc/xinetd.d/rsh

Next, you have to edit file /etc/securetty to append rsh at the end of it.

# ( grep rsh /etc/securetty ) || ( echo "rsh" >> /etc/securetty )

Now, you can restart xinetd to start rsh.

# service xinetd restart

For each user who wants to use rsh to run commands on remote machines, edit files ~/.rhosts on remote machines to include the hostname or IP address of the local machine. For example, a typical .rhosts file looks like follows.

master
compute-0-0
compute-0-1
compute-0-2

The user on a machine that has such .rhosts file in the home directory allows others from hosts master, compute-0-0, compute-0-1, compute-0-2 run a command on it. Check the man page of rhosts for advanced options.

If you meet some errors related to "back connection", please turn off the firewall of the local machine or at least open ports in range 1011 to 1023, which is normally used for back connection in rsh protocol. By the way, port 514 should be opened on the remote machine too.

Decode .HQX File on Linux

A very simple solution is to use UUDeview which is available in many Linux distros. You can also use macutils on Debian-based distros. Or even easier, an online tool is here.

On Fedora:

# yum install uudeview

On Debian/Ubuntu:

# apt-get install uudeview

To decode file fxppd1110bm922ien.hqx, for example, you can use the following command.

$ uudeview -i fxppd1110bm922ien.hqx

Have a good day!

How to Set up Hadoop 1.0.0 on RHEL/CentOS

Finally, Hadoop 1.0.0 was released yesterday after six years :).

My research field is Natural Language Processing, and I have used Nutch (with Hadoop) since 2007. I have been following news and articles on Hadoop for a long time, but I have not set up any new version for about two years. However, I were very surprised when I visited Hadoop website today because of... the version 1.0.0. It is obviously that I immediately downloaded and installed it on my server.

Now, I will note steps that I used to setup Hadoop to run on single node, fix some minor errors, and test it. It is very easy to install Hadoop nowadays, much much much easier than two years ago.

Some information about my server:

• Server: DELL, Intel Xeon X3450 @ 2.67GHz (4 cores, HT enabled).
• RAM: 8.0 GB
• OS: Red Hat Enterprise Linux Server release 6.2 (Santiago)

Based on the information that I collected in the installation process, there is no difference if you use CentOS 6, or even RHEL/CentOS 5.

Requirements:

• Oracle JDK 1.6 (I am not sure whether it works well with OpenJDK or Oracle JDK 1.7.)

Now, we begin...

Step 1. Download and install Oracle JDK 1.6 from Oracle Java SE site. I used jdk-6u30-linux-x64-rpm.bin. I do the following commands in my Linux box.

# wget http://download.oracle.com/otn-pub/java/jdk/6u30-b12/jdk-6u30-linux-x64-rpm.bin
# chmod +x jdk-6u30-linux-x64-rpm.bin
# ./jdk-6u30-linux-x64-rpm.bin

Make sure that JDK was installed to directory /usr/java/default, in which default is a symbolic link to latest and latest is, in turn, a symbolic link to jdk1.6.0_30. Hadoop will use this default location to run regardless of the default version of Java on your system, such as OpenJDK.

Step 2. Download and install Hadoop. Hadoop 1.0.0 is shipped with many packages including source, general binary, rpm, and deb for both 32-bit OS (i386) and 64-bit OS (amd64). I used hadoop-1.0.0-1.amd64.rpm because my OS is RHEL 64-bit. If you use Debian, please use .deb package.

# wget http://ftp.jaist.ac.jp/pub/apache/hadoop/common/hadoop-1.0.0/hadoop-1.0.0-1.amd64.rpm
# rpm -ivh hadoop-1.0.0-1.amd64.rpm

Very easy, and very fast, huh!!!

Step 3. Set up Hadoop for using on single node. This step shows how the installation is too easy.

# hadoop-setup-single-node.sh

Answer "yes" (y) for all questions. After the setup has finished, services of Hadoop will be started automatically, including hadoop-namenode, hadoop-datanode, hadoop-jobtracker, and hadoop-tasktracker.

Step 3a. Fix a minor bug.

All four services seem to be started successfully. However, Hadoop is at 1.0.0, it should have some bugs :D. Indeed, there is at least a bug related to the mapredsystem directory on HDFS that makes hadoop-jobtracker cannot start although it said OK when you started the service. You can check the log file for more details. It is located under /var/log/hadoop/mapred/ with the name hadoop-mapred-jobtracker-$HOSTNAME.log. The log might have a portion look as follows.

WARN org.apache.hadoop.mapred.JobTracker: Failed to operate on mapred.system.dir (hdfs://localhost:8020/mapred/mapredsystem) because of permissions.
WARN org.apache.hadoop.mapred.JobTracker: Manually delete the mapred.system.dir (hdfs://localhost:8020/mapred/mapredsystem) and then start the JobTracker.
WARN org.apache.hadoop.mapred.JobTracker: Bailing out ...
org.apache.hadoop.security.AccessControlException: org.apache.hadoop.security.AccessControlException: Permission denied: user=mapred, access=WRITE, inode="":hdfs:supergroup:rwxr-xr-x

The log said that Hadoop cannot operate the system directory of Map-Reduce /mapred/mapredsystem since user is mapred and owner is hdfs. Furthermore, the directory owner does not allow others to write on it. I check the details by using the following command.

# hadoop fs -ls /
drwxrwxrwx   - hdfs   supergroup          0 2011-12-28 20:08 /tmp
drwxr-xr-x   - hdfs   supergroup          0 2011-12-28 21:46 

What??? I did not see the directory /mapred. Hadoop might have a bug in the installation script. I fixed it by creating /mapred using hdfs user and change the owner of that directory to mapred user.

# sudo -u hdfs hadoop fs -mkdir /mapred
# sudo -u hdfs hadoop fs -chown mapred /mapred

Restart JobTracker.

# service hadoop-jobtracker restart

I checked the log file again, and everything was ok.

Step 4. Test Hadoop.

Hadoop 1.0.0 has been shipped with an example to validate the setup process. Run it as follow.

# hadoop-validate-setup.sh --user=hdfs

If you get "teragen, terasort, teravalidate passed." near the end of the output, everything is ok.

You can check the progress by accessing JobTracker website via http://localhost:50030/.

You can also check nodes by accessing NameNode website via http://localhost:50070/.

I will try to setup a new Hadoop cluster in this New Year Holiday, and put my notes on this blog ASAP.

Enjoy your New Year Holiday!!!

How to Change MAC Address on RHEL/CentOS/Fedora

On the RHEL/CentOS/Fedora boxes, there is a line named HWADDR in the interface configuration file /etc/sysconfig/network-scripts/ifcfg-eth0, for example, storing the MAC address of the corresponding ethernet interface.

Nothing will happen if you change the MAC addresss in this line, and you will probably receive the following notice when restart the network service.

Shutting down interface eth0:  Device eth0 has MAC address AA:BB:CC:DD:EE:FF, instead of configured address 00:11:22:33:44:55. Ignoring.

To change the MAC address, just keep the HWADDR as it is, and add the following line to the above file.

MACADDR=00:11:22:33:44:55

Restart the network service.

# service network restart
# ifconfig eth0

New MAC address! Congrats!!!

Note: You should change eth0 to eth1, or the Ethernet interface you want to change its MAC address.