Month: July 2012

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();