Category: Computers

All things computing.

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”

Solution for MySQL ERROR 1396 (HY000): Operation CREATE USER failed for

Posted on by rchapin

This indicates that the user already exists, or did exist but that all of the data for that user has not been deleted.

As the mysql root user:

REVOKE ALL PRIVILEGES, GRANT OPTION FROM 'user'@'hostname';
DROP USER 'user'@'hostname'

Then re-try creating the user.→ Continue reading “Solution for MySQL ERROR 1396 (HY000): Operation CREATE USER failed for”

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”

[SOLVED] java.lang.NoSuchMethodError: org.apache.avro.generic.GenericData.createDatumWriter When Using Avro Data with MapReduce

Posted on by rchapin

I am working on a project and have decided to use Avro for the data serialization format.

I encountered the following error when trying to set up the unit test to test the mapper implementation through Eclipse:

java.lang.NoSuchMethodError: org.apache.avro.generic.GenericData.createDatumWriter(Lorg/apache/avro/Schema;)Lorg/apache/avro/io/DatumWriter;
    at org.apache.avro.hadoop.io.AvroSerialization.getSerializer(AvroSerialization.java:114)
    at org.apache.hadoop.io.serializer.SerializationFactory.getSerializer(SerializationFactory.java:82)
    at org.apache.hadoop.mrunit.internal.io.Serialization.copy(Serialization.java:67)
    at org.apache.hadoop.mrunit.internal.io.Serialization.copy(Serialization.java:98)
    at org.apache.hadoop.mrunit.internal.io.Serialization.copyWithConf(Serialization.java:111)
    at org.apache.hadoop.mrunit.TestDriver.copy(TestDriver.java:676)
    at org.apache.hadoop.mrunit.TestDriver.copyPair(TestDriver.java:680)
    at org.apache.hadoop.mrunit.MapDriverBase.addInput(MapDriverBase.java:120)
    at org.apache.hadoop.mrunit.MapDriverBase.addInput(MapDriverBase.java:130)
    at org.apache.hadoop.mrunit.MapDriverBase.addAll(MapDriverBase.java:141)
    at org.apache.hadoop.mrunit.MapDriverBase.withAll(MapDriverBase.java:247)
    at com.ryanchapin.hadoop.mapreduce.mrunit.UserDataSortTest.testMapper(UserDataSortTest.java:111)
    at sun.reflect.NativeMethodAccessorImpl.invoke0(Native Method)
    at sun.reflect.NativeMethodAccessorImpl.invoke(NativeMethodAccessorImpl.java:62)
    at sun.reflect.DelegatingMethodAccessorImpl.invoke(DelegatingMethodAccessorImpl.java:43)
    at java.lang.reflect.Method.invoke(Method.java:497)
    at org.junit.runners.model.FrameworkMethod$1.runReflectiveCall(FrameworkMethod.java:45)
    at org.junit.internal.runners.model.ReflectiveCallable.run(ReflectiveCallable.java:15)
    at org.junit.runners.model.FrameworkMethod.invokeExplosively(FrameworkMethod.java:42)
    at org.junit.internal.runners.statements.InvokeMethod.evaluate(InvokeMethod.java:20)
   
→ Continue reading “[SOLVED] java.lang.NoSuchMethodError: org.apache.avro.generic.GenericData.createDatumWriter When Using Avro Data with MapReduce”

Configuring Hidden, Invisible, or Whitespace Characters in The Eclipse Text Editor

Posted on by rchapin

The newer (I am currently using Mars, 4.5.0) versions of Eclipse provide very good tools for configuring the visibility of whitespace characters in code.

To customize your settings go to Window -> Preferences -> General -> Editors -> Text Editors.

On that page there will be checkbox option next to “Show whitespace characters (configure visibility).

Clicking on the ‘configure visibility’ link will allow you to choose what is shown and the opacity of the whitespace characters, which is a really → Continue reading “Configuring Hidden, Invisible, or Whitespace Characters in The Eclipse Text Editor”

[SOLVED] Configuring chrooted bind and rndc-confgen Hangs Not Generating a Key

Posted on by rchapin

I am putting together a chrooted installation of named and ran into a problem whereby attempting to generate an rndc.key with rndc-confgen just hangs, never returning and not generating a key.

After doing some searching I discovered that I needed to run the command as follows:

rndc-confgen -a -r /dev/urandom  -t /var/named/chroot

Which outputs the following, generating the key file that I expected.

wrote key file "/etc/rndc.key"
wrote key file "/var/named/chroot/etc/rndc.key"

→ Continue reading “[SOLVED] Configuring chrooted bind and rndc-confgen Hangs Not Generating a Key”

© 2005 Ryan Chapin