Category: Software

Dynamically Instantiating Classes in Python

Posted on by rchapin

A common design pattern is to define a class or list of classeses in configuration such that at runtime the classes can be dynamically instantiated.

I’ve done this before in many other languages and had need to do so today in Python (2.7.11)

It seems as though the clean way to do so is by using the Pyton importlib module.  By using it, it enables you to cleanly dynamically import sub modules

Following is an example:

import importlib

klass_1_module =
→ Continue reading “Dynamically Instantiating Classes in Python”

Java PowerMock Could not reconfigure JMX java.lang.LinkageError Solution

Posted on by rchapin

If you are using Mockito and PowerMock to build mocks for your Java tests and you run into the following error:

2016-05-05 17:31:20,204 main ERROR Could not reconfigure JMX java.lang.LinkageError: loader constraint violation: loader (instance of org/powermock/core/classloader/MockClassLoader) previously initiated loading for a different type with name "javax/management/MBeanServer"
        at java.lang.ClassLoader.defineClass1(Native Method)
        at java.lang.ClassLoader.defineClass(ClassLoader.java:760)
        at org.powermock.core.classloader.MockClassLoader.loadUnmockedClass(MockClassLoader.java:238)
        at org.powermock.core.classloader.MockClassLoader.loadModifiedClass(MockClassLoader.java:182)
        at org.powermock.core.classloader.DeferSupportingClassLoader.loadClass(DeferSupportingClassLoader.java:70)
        at java.lang.ClassLoader.loadClass(ClassLoader.java:357)

Simply add the following as a class level annotation:

@PowerMockIgnore( {"javax.management.*"} )

→ Continue reading “Java PowerMock Could not reconfigure JMX java.lang.LinkageError Solution”

Blacklisting Kernel Modules

Posted on by rchapin

Following is a walkthrough on how to blacklist a kernel module.  The specific example is blacklisting the nouveau driver so that I can install the OEM Nvidia driver.

1. First, blacklist the nouveau driver: Add a line to the textfile /etc/modprobe.d/nouveau-blacklist.conf that contains they keyword ‘blacklist’ and the name of the driver

blacklist nouveau

2. Rebuild the initramfs image file.  First, backup existing initramfs

mv initramfs-3.10.0-327.18.2.el7.x86_64.img initramfs-3.10.0-327.18.2.el7.x86_64.img_2016-06-09.bak

Build new initramfs

dracut -v /boot/initramfs-$(uname -r).img $(uname -r)

3. Reboot the system → Continue reading “Blacklisting Kernel Modules”

How to Configure a User Account in Active Directory So that the Password Never Expires

Posted on by rchapin

Using ADSI Edit, navigate to the user in question.  Right-click on the user and select Properties.

Then, scroll down to the ‘userAccountControl’ property and click the Edit button.

Enter 66048 into the field and then click ‘OK’ and then ‘Apply’.

After closing the edit window, scroll to the right to confirm that the value indicates the following

'0x10200 = (NORMAL_ACCOUNT|DONT_EXPIRE_PASSWORD)'
→ Continue reading “How to Configure a User Account in Active Directory So that the Password Never Expires”

Using netcat to Mock a RESTful Webservice that Returns JSON

Posted on by rchapin

Let’s say that you are working on a part of a project that needs to consume some JSON data from a forthcoming HTTP service.  That sub-system is being developed by one of your colleagues and is not yet ready for you to stand-up to develop against.

You can use netcat to mock the webservice and return some static JSON data for which you can develop and test against with a simple one-liner.

First, put together your JSON in a file, → Continue reading “Using netcat to Mock a RESTful Webservice that Returns JSON”

How to Use Credentials That Contain Special Characters with curl

Posted on by rchapin

In order to execute curl commands to endpoints with passwords that contain special characters, the cleanest way that I have found to do so is to Base64 encode the authentication string for curl and then pass an Authorization request header along with the request.

In this example the credentials are uid ‘rchapin’ and passwd ‘abc123!@#’.  Normally we would pass this to curl as follows:

$ curl -u rchapin:abc123!@# -X GET https://some-endpoint:443

However, this will not work and the password will → Continue reading “How to Use Credentials That Contain Special Characters with curl”

How to Configure a Linux Client for Active Directory Authentication

Posted on by rchapin

I am currently working on setting up multiple environments for a new project (DEV, QA, and PROD) and will be integrating all of the servers to an Active Directory Domain Controller for user management.

Following are notes from when I configured a Fedora Core 18 laptop to integrate with an AD server.  It is likely things have changed some from then and I will update this as required for a current version of RHEL7/CentOS 7.

Install the following packages

yum
→ Continue reading “How to Configure a Linux Client for Active Directory Authentication”

[SOLVED] Delete key not working with x2go server running XFCE

Posted on by rchapin

I am working with a development environment whereby I VPN into an environment with an Ubuntu VirtualBox guest and then initiate an x2go client session to a developement workstation server that lives in the development environment.

I had everythining working exactly as I wanted except that the Delete key did not work in the x2go session.

Previously the xev output when pressing the delete key was:

FocusOut event, serial 36, synthetic NO, window 0x2e00001,
    mode NotifyGrab, detail NotifyAncestor

FocusIn event,
→ Continue reading “[SOLVED] Delete key not working with x2go server running XFCE”

Looping Through a List of Files with Spaces in the File Name with Bash

Posted on by rchapin

If you have a list of files that you want to operate on in a loop in bash and some of them have spaces in the file name the default IFS (Internal Field Separator) will match with the space and tokenize the file.

The simple approach is to temporarily set the IFS as follows.  This can be done in a shell script, but the following example is directly on the command line for ‘one-liner’ usage.

OIFS="$IFS"

IFS=$'\n' 

for i in
→ Continue reading “Looping Through a List of Files with Spaces in the File Name with Bash”

How To Remove the Byte Order Mark (BOM) from UTF-8 Encoded Text Files

Posted on by rchapin

The easiest way that I have seen so far for doing so is to use tail and simply read everything except the first three bytes (start reading at the 4th byte), as follows:

tail --bytes=+4 text_file.txt text_file-wo-bom.txt
→ Continue reading “How To Remove the Byte Order Mark (BOM) from UTF-8 Encoded Text Files”
© 2005 Ryan Chapin