Ryan Chapin's Website

Eclipse (at least Juno) will complain that there is “No grammar constraints (DTD or XML Schema) referenced in the document.”, even though there is no DTD for Ant build.xml files (see here for Ant faq about DTD for build.xml files).

To surpress the warning in Eclipse add

<!DOCTYPE project>

After the <?xml . . . XML declaration tag

 

If you want to get a 64-bit build of Firefox for Linux, go to the following URL and browse to the most recent version, download and install.

http://releases.mozilla.org/pub/mozilla.org/firefox/releases/

To specify the proxy information for svn edit the servers file in the .subversion directory under Linux, or the Subversion directory under the user’s directory in Windows.

Add the following under the [global] section:

http-proxy-host = someurl.com
http-proxy-port = 80
http-proxy-username = uid
http-proxy-password = passwd
http-compression = no

Following is a quick howto for installing the NoMachine free version of NXServer:

. Make sure that you have a DNS entry for the hostname of your NX Server machine or an entry in the server’s /etc/hosts file that points to it’s IP.

. rpm -i nxclient-3.5.0-7.x86_64.rpm
. rpm -i nxnode-3.5.0-7.x86_64.rpm
. rpm -i nxserver-3.5.0-9.x86_64.rpm

. copy stock config file to server.cfg:
        . # cd /usr/NX/etc
        . # cp server.cfg server.cfg_oem
        . # cp server-redhat.cfg.sample server.cfg

. edit config files:
        . /usr/NX/etc/server.cfg: ensure that the following values are set:
                . EnablePasswordDB = “0”
                . EnableStatistics = “0”
                . EnableNodeMonitoring = “0”
                . EnableUserProfile = “0”

        . /usr/NX/etc/node.cfg
                . EnableSensor = “0”

. generate SSH keys:
        . /usr/NX/bin/nxserver –keygen
        . use the key: /usr/NX/share/keys/default.id_dsa.key in the NX Client config when making a connection to your server

I am setting up a vm running CentOS 6.2 and want to be able to connect to it via NXClient.

After doing the basic install and getting the key from the server I got the following error when trying to login on the client side:

Server configuration error. Cannot log in.  Please contact your system administrator

Looking at /var/log/messages on the server revealed the following (hostName is the name of the host for the machine, changed from the actual nameof the box):

Aug 30 10:21:30 hostName NXNODE-3.5.0-9[12117]: ERROR: NX> 596 ERROR: NXNODE Ver. 3.5.0-9  (Error id eAE8C74) [eAE8C74] Logger::log nxnode 2963
Aug 30 10:21:30 hostName NXNODE-3.5.0-9[12117]: ERROR: NX> 596 ERROR: create session: run commands [eAE8C74] Logger::log nxnode 2963
Aug 30 10:21:30 hostName NXNODE-3.5.0-9[12117]: ERROR: NX> 596 ERROR: execution of last command failed [eAE8C74] Logger::log nxnode 2963
Aug 30 10:21:30 hostName NXNODE-3.5.0-9[12117]: ERROR: NX> 596 last command: /usr/bin/xauth -v -f /home/rchapin/.nx/C-hostName-1004-3C32B952A4DB53BE56F707B06E917F71/authority source /home/rchapin/.nx/C-hostName-1004-3C32B952A4DB53BE56F707B06E917F71/scripts/authority [eAE8C74] Logger::log nxnode 2963
Aug 30 10:21:30 hostName NXNODE-3.5.0-9[12117]: ERROR: NX> 596 exit value: 1 [eAE8C74] Logger::log nxnode 2963

I realized after seeing this that I did not have a DNS entry for the hostName machine and xauth failed because it could not resolve it.

In this case, I added a entry in /etc/hosts for the host name and was then able to fire up the NXClient session.

If you need to get a Windows command prompt as the Administrator do the following:

• Click on ‘Start’
• Type the following in the search/command input field:

• runas /user:administrator cmd

Attached to this post is a tar.gz file that contains a complete template with which you can build a Java project.  It includes the directory structure, sample ant build.xml, logging configs, and shell scripts (and the beginnings of some Windows scripts) to run the program:

java_project_template/README.txt
java_project_template/conf/
java_project_template/conf/log4j.properties
java_project_template/lib/
java_project_template/lib/log4j-1.2.16.jar
java_project_template/launch.sh
java_project_template/scripts/
java_project_template/scripts/run.sh
java_project_template/scripts/run.vbs
java_project_template/scripts/run.bat
java_project_template/src/
java_project_template/src/com/
java_project_template/src/com/ryanchapin/
java_project_template/src/com/ryanchapin/samples/
java_project_template/src/com/ryanchapin/samples/java/
java_project_template/src/com/ryanchapin/samples/java/Example.java

The ant build file will create a build/classes directory into which all of the Java .class files are compiled.  It will also create a dist directory into which all of the jars, configs, and scripts to run the program are placed.

The run.sh script will dynamically concatenate the classpath argument for java based on the contents of the dist/lib/ directory and can be customized to accept any additional command line arguments that you may require.

The conf/ directory includes a log4j.properties file to get you started.

The build.xml file includes default, clean, and dist targets and does all of the basics needed to build your project.

The launch.sh script is used primarily during development to invoke run.sh without having to cd into the dist folder each time it is run.

The following is a quick howto for when you want to fire up a process as a non-root user on boot under Linux:

Create a script, typically under /usr/bin with something similar to the following:

#!/bin/bash

# invoke your process

/usr/local/process/someprocess

exit

Now, add an entry to /etc/rc.d/rc.local to invoke the command as the non-root user

su – [non-root-user] -c [path-to-shell-script]

Make sure that the exit command is the last thing in the shell script so that you will exit the su and rc.local will continue processing as the root user.

When developing JavaEE applications in Eclipse it is more or less necessary to have all of the JavaEE libraries on the build path.

To do so, do the following:

• Unpack the version of the JavaEE application server that you are using.  In this case it is JBoss 6.0.0.Final.
• Run the ‘Add a Server’ wizard under the JavaEE perspective’s Server tab.
• Add the Server Runtime to the build path/libraries:

• Right-click on your project and select ‘Build Path/Configure Build Path’
• Click on the ‘Libraries’ tab
• Click on ‘Add Library’
• Select ‘Server Runtime’
• Select the JBoss Runtime declared server (from the step above)

Java enables you to exectute a process on the host OS and to provide input (STDIN) to the process and read standard out (STDOUT) and standard error (STDERR).  Each time that you execute a process via Runtime.exec() or ProcessBuilder.start() STDIN, STOUT, and STDERR are piped to the running JVM as an OutputStream or InputStream.  For each stream there are two file descriptors and typically when the process terminates those streams are closed also closing the two file descriptors.

Even if you destroy the Process via Process.destroy() you may still be leaking file descriptors.  The typical symptoms are as follows:

1. You see a growing number of named pipes in the output of lsof:

java      8654 rchapin   23w     FIFO        0,6        0t0      26015 pipe
java      8654 rchapin   24r     FIFO        0,6        0t0      26016 pipe
java      8654 rchapin   26r     FIFO        0,6        0t0      26017 pipe
java      8654 rchapin   30w     FIFO        0,6        0t0      26031 pipe
java      8654 rchapin   31r     FIFO        0,6        0t0      26032 pipe
java      8654 rchapin   33r     FIFO        0,6        0t0      26033 pipe
java      8678 rchapin    0r     FIFO        0,6        0t0      26015 pipe
java      8678 rchapin    1w     FIFO        0,6        0t0      26016 pipe
java      8678 rchapin    2w     FIFO        0,6        0t0      26017 pipe
java      8680 rchapin    0r     FIFO        0,6        0t0      26031 pipe
java      8680 rchapin    1w     FIFO        0,6        0t0      26032 pipe
java      8680 rchapin    2w     FIFO        0,6        0t0      26033 pipe

2. You start seeing the ‘Too many open files’ error in your log:

2012-07-06 02:39:27,260 (ERROR) (Thread-6) java.io.IOException: error=24, Too many open files

A good practice is to make sure to get a reference to each of the Streams and to explicitly close them, REGARDLESS of whether you actually utilize those streams.

Example:

Process process = Runtime.getRuntime.exec(“some command here”);
or
ProcessBuilder processBuilder = new ProcessBuilder(someCommandArray);
Process process = processBuilder.start();

// To close them
process.getInputStream().close();
process.getOutputStream().close();
process.getErrorStream().close();