Every day is a discovery

Useful Yum commands

noreply@blogger.com (Rakesh Nerella) — Tue, 12 Feb 2019 07:38:00 +0000

Few useful yum commands

yum list installed - Gives a list of already installed packages
yum history list - Gives a list yum installs. Note that one can install multiple packages and their dependencies in a single invocation. Example, yum install docker-ce, docker-ce-cli
yum history info - Gives the details of yum invocation for each of the historical entry above.
/var/log/yum.log - also contains log of yum installs
yum list docker-ce --showduplicates | sort -r - Shows all the versions that are present for docker and sorts them.

To find difference in packages between installs -

Before installation -

rpm -qa --qf '%{NAME}.%{ARCH}\n' | sort > old-installed-rpms.txt

After installation -

rpm -qa --qf '%{NAME}.%{ARCH}\n' | sort > new-installed-rpms.txt

Diff -

diff old-installed-rpms.txt new-installed-rpms.txt | grep '^<'

Remote Interview Tools, Online Java Compilers & Cloud hosted IDE

noreply@blogger.com (Rakesh Nerella) — Tue, 22 Mar 2016 11:31:00 +0000

Very good for Interviews (Basic stuff available for free, advanced features on purchase)

Basic Online Compilers (Free or Ad-supported)

Cloud Hosted IDE (Paid services only)

Cloud9 - Supported Languages
Nitrous - Java on Nitrous
Koding - Features
Sourcelair - Supported Languages
Bonus - Crisp comparison of Cloud hosted IDE (Published Date : Aug 2014. So, it may not cover any recent updates)

Modify Windows Control Panel Settings from command-line

noreply@blogger.com (Rakesh Nerella) — Tue, 20 Jan 2015 13:00:00 +0000

I recently discovered that many Control Panel settings in windows can be opened from command-line. The article from Microsoft How to run Control Panel tools by typing a command explains.

Windows Command line shortcut to set Environment Variables

noreply@blogger.com (Rakesh Nerella) — Tue, 20 Jan 2015 12:43:00 +0000

In order to invoke the System window and later set the Environment variables, the below command-line could be handy. It will avoid some mouse-clicks :)

C:\windows\system32>control.exe sysdm.cpl,System,3

The above command can also be saved into a bat file and placed conveniently on Windows Desktop.

Useful websites

noreply@blogger.com (Rakesh Nerella) — Thu, 06 Nov 2014 17:16:00 +0000

25 Lifehack websites

101 Useful websites

e-Learning related websites (MOOC or similar)

noreply@blogger.com (Rakesh Nerella) — Tue, 04 Nov 2014 15:29:00 +0000

Coursera
Khan Academy
Udacity
edX
Academic Earth
Duo Lingo - Learn languages
MIT Open Courseware
codecademy - coding languages
Learn Street - coding languages
Udemy - Coding, Design etc

New Think Tank - Excellent collection of video tutorials for Java, OOPS, Algorithms, UML etc

MOOC List - A collection of MOOC (Massive Open Online Course) -
piazza - Learning University collaboration -
Cosmo Learning - Online Videos -
Learn Now Online - Online Videos for Developer, Manager etc (MS .Net, Java, PMP, MS Office etc)

tar destination directory

noreply@blogger.com (Rakesh Nerella) — Thu, 18 Sep 2014 13:49:00 +0000

tar by default extract's to the current directory, if that needs to be changed, it can be done by using below -

[rakesh@host2] tar zxvf source.tar -C /your/dest/dir/to/extract

Graphic display in Linux

noreply@blogger.com (Rakesh Nerella) — Thu, 18 Sep 2014 13:39:00 +0000

In Oracle Linux Virtual Box VM, by default the graphic output is disabled. Login as root (su) and edit the file /etc/inittab as shown below

Subsequently from the command prompt run startx to start the graphic display.

It's possible that despite the above changes, errors like below may occur

[bea@vin2 Desktop]$ java -jar wls1036_generic.jar 
Xlib: connection to ":0.0" refused by server
Xlib: Invalid MIT-MAGIC-COOKIE-1 key
Unable to instantiate GUI, defaulting to console mode.

Solution:

Login as root and copy and override the .Xauthority from root's home folder to the user's home folder. As a precaution, take a backup of the user's .Xauthority file.

You can check if the graphic display is working or not by running xclock

Java Https

noreply@blogger.com (Rakesh Nerella) — Fri, 13 Dec 2013 09:28:00 +0000

Some links on Java https

http://download.java.net/jdk7/archive/b123/docs/api/index.html?javax/net/ssl/HttpsURLConnection.html

http://hc.apache.org/httpclient-3.x/sslguide.html

http://hc.apache.org/httpclient-3.x/apidocs/index.html

http://code.google.com/p/jsslutils/wiki/ApacheHttpClientUsage

http://stackoverflow.com/questions/14392120/java-program-to-connect-to-a-secured-url-https-and-check-if-we-are-getting

http://stackoverflow.com/questions/1828775/how-to-handle-invalid-ssl-certificates-with-apache-httpclient

http://stackoverflow.com/questions/3038026/using-java-class-httpsurlconnection

How to insert a text every x rows in Notepad++?

noreply@blogger.com (Rakesh Nerella) — Mon, 18 Nov 2013 07:47:00 +0000

Google search brought me to How to insert a line break every 5 rows in Excel/Word/Notepad++?

Using the suggested regex from the above source, replace the number 5 with x and replace \n with any text.

For example, to insert a commit; after every 100 lines in a sql script. This would be the regex -

Find : ((.*\s*\n\s*){100})
Replace : $1commit;\n

Excel: Copy formula to tens of thousands of rows

noreply@blogger.com (Rakesh Nerella) — Mon, 18 Nov 2013 06:45:00 +0000

Check the Quickly Copy Excel Formula Down to achieve it.

Note that it only works if there is data in the adjacent column only. So if the data is on column A and formula to be copied is on column C, then it will NOT work. The formula to be copied has to be on column B.

User names and tablespace names

noreply@blogger.com (Rakesh Nerella) — Mon, 18 Nov 2013 05:01:00 +0000

Select all schema user names

select username from dba_users;

Select all tablespace names

select tablespace_name from dba_tablespaces;

Create a simple tablespace

CREATE TABLESPACE POOL_TS
  DATAFILE 'pool_ts.dat'
  SIZE 20M AUTOEXTEND ON;

Your Message Wasn’t Delivered Because Of Security Policies

noreply@blogger.com (Rakesh Nerella) — Sun, 10 Nov 2013 04:36:00 +0000

Java Mail API can be used to send emails. For a mail to be sent, at the minimum the following need to present -

Mail Server Host and Port [Mandatory]
Sender email id [Optional, can be a dummy mail id]
Receiver email id [Mandatory]

If the mail server is Microsoft Exchange, there could be a policy that requires sender authentication. It means that sender also needs to be a valid authenticated user. If a dummy mail id is used as sender, then MS Exchange would not let the mail be delivered.

In that event, the following articles explain how that can be disabled.

Note that the above settings need to be performed on the MS Exchange Mail Server. If MS Exchange Mail server cannot be accessed, then a valid sender needs to be used!

Dual label header cell split diagonally

noreply@blogger.com (Rakesh Nerella) — Sun, 10 Nov 2013 02:39:00 +0000

Simple instructions to create Split cell diagonal. The article starts with angled text; scroll down a little bit.

Microsoft Excel - How to create a combination chart of Bar & Line and Secondary axis

noreply@blogger.com (Rakesh Nerella) — Sun, 10 Nov 2013 01:52:00 +0000

Official Microsoft guide to Present your data in a combination chart

By default, there is only one vertical or horizontal axis called the Primary axes. One can Add or remove a secondary axis in a chart should you require it.

Oracle append string to select query

noreply@blogger.com (Rakesh Nerella) — Fri, 01 Nov 2013 10:23:00 +0000

Append in a select statement can be achieved via the || operator.

select 'Mr.' || name from employee e where e.sex = 'M'

select case when e.sex = 'M' then 'Mr.' else 'Ms.' end || name as salutation_name from employee e

Oracle XE 11gR2 installation – “OracleXEService should not be installed already”

noreply@blogger.com (Rakesh Nerella) — Fri, 31 May 2013 06:53:00 +0000

A simple guide on how to resolve Oracle XE 11gR2 installation failure. This error occurs when you are trying to install Oracle XE after successful un-install from Windows Control Panel.

Oracle XE 11gR2 installation – “OracleXEService should not be installed already”

Just make sure that Command Prompt is started using "Run as Administrator"

Eclipse Xquery plugin and editor

noreply@blogger.com (Rakesh Nerella) — Fri, 24 May 2013 04:55:00 +0000

XQuery Development Tools Installation provides simple instructions to install XQDT and Zorba Xquery adapter.

In summary, you need to add the remote site http://download.eclipse.org/webtools/incubator/repository/xquery/milestones/ and install XQDT Core Features .

If your are using Eclipse 3.8 Juno or above, Cannot Install XQDT in Eclipse Error may occur.

Cannot complete the install because one or more required items could not be found.
  Software being installed: XQuery Development Tools Feature 0.8.0.201107251305 (org.eclipse.wst.xquery.feature.feature.group 0.8.0.201107251305)
  Missing requirement: XQDT Core Plug-in 0.8.0.201107251305 (org.eclipse.wst.xquery.core 0.8.0.201107251305) requires 'bundle org.eclipse.dltk.core [3.0.0,4.0.0)' but it could not be found
  Cannot satisfy dependency:
    From: XQuery Development Tools Feature 0.8.0.201107251305 (org.eclipse.wst.xquery.feature.feature.group 0.8.0.201107251305)
To: org.eclipse.wst.xquery.core [0.8.0.201107251305]

In order to overcome this issue, as suggested in the stackoverflow answer, install DLTK 3.0.0 from Eclipse Indigo update site - http://download.eclipse.org/releases/indigo.

You can also consider installing from DLTK Downloads directly any DLTK version that is greater than or equal to 3.0.0 but less than 4.0.0.

Java ClassNotFoundException and NoClassDefFoundError

noreply@blogger.com (Rakesh Nerella) — Fri, 10 Feb 2012 04:23:00 +0000

These responses http://stackoverflow.com/a/3198490/37144 and http://stackoverflow.com/a/2213496/37144 do not have many up votes but in my opinion they are the best ones.

A very useful tool used for locating class files - JarScan. It has an online version and offline version that can be used for searching local file system. However, the online version's database isn't too big and might not auit everyone'e requirement. For that, one can visit findJar

Play Videos on HP TouchPad

noreply@blogger.com (Rakesh Nerella) — Thu, 09 Feb 2012 19:15:00 +0000

Or Free media player for HP TouchPad.

Before I talk about the free option. Let me just say that by far the best media player on HP TouchPad is available at KalemSoft. It costs $4.99 at the time of this writing.

The best free alternative at the time of this writing is TouchPlayer. All the required instructions to install it are available at the same location.

HP TouchPad WebOS Preware Installation

noreply@blogger.com (Rakesh Nerella) — Thu, 09 Feb 2012 19:05:00 +0000

Why Preware?
WebOS Quick Install can be used to install Apps using .ipk files onto the TouchPad that are not part of HP Catalog. There are 2 main disadvantages -

The device needs to be always connected another laptop/desktop.
If an app has dependencies on any other app that are not already installed, the .ipk may not install successfully.

Install Preware

The latest version of Preware installer ipk can be found Preware Downloads. Install it using WebOS Quick Install just like any other app.

On successful installation, Preware icon can be found in the Downloads tab of HP TouchPad Launcher.

TODO: TouchPad Downloads tab screenshot here

References : http://www.webosbuzz.com/hp-touchpad/633-how-install-preware-onto-hp-touchpad.html

WebOS Quick Install

noreply@blogger.com (Rakesh Nerella) — Sun, 29 Jan 2012 16:11:00 +0000

WebOS Quick Install can be used to install applications not included in the official HP Catalog. It can be used for HP TouchPad or any other WebOS devices. WebOS Quick Install is developed by Jason Robitaille. The latest version of WebOS Quick Install along with the installation requirements and instructions can be found here.

Before launching WebOS Quick Install, the device needs to be connected to the laptop/desktop via USB cable in Developer Mode.

Activate Develop Mode in HP TouchPad

Turn on your Touchpad and press the home button. Tap the "just type" area and enter webos20090606.

Tap the "Developer Mode" icon that appears. Tap the "on/off" slider in the top right corner of the next screen, but leave the "DEVELOPER MODE PASSWORD" field blank. Tap "Submit".

TODO: Screenshot of Dev Mode Window

Launch WebOS Quick Install
WebOS Quick Install is a Java application. Try to have a latest version of Java installed on your laptop/desktop. Execute the WebOSQuickInstall-xxx.jar as a Java application. The first time it's launched, it installs some drivers.

Any *.ipk files can be chosen and installed on the HP Touch Pad.

References : http://lifehacker.com/5836294/supercharge-your-new-hp-touchpad-with-preware

What is an xs:NCName type and when should it be used?

noreply@blogger.com (Rakesh Nerella) — Sun, 04 Dec 2011 09:59:00 +0000

Came across a very good link on xs:NCName with the same title as above in stackoverflow.com - What is an xs:NCName type and when should it be used?

Unlock account in Oracle Database (ORA-28000)

noreply@blogger.com (Rakesh Nerella) — Wed, 06 Oct 2010 11:57:00 +0000

An oracle database account can get locked for several reasons. The most common reason is number of unsuccessful attempts. This typically give the following error :

ORA-28000: the account is locked

Account can be unlocked by logging in as 'sys' user and issuing the following command:

SQL> alter user scott identified by tiger account unlock;

Setup EJB 3 MDB on Weblogic using Eclipse

noreply@blogger.com (Rakesh Nerella) — Tue, 13 Jul 2010 14:59:00 +0000

Setup EJB 3 MDB Project on Eclipse Shown below is a common exception which occurs when class is executed from Eclipse that depends on Weblogic libraries -

Exception in thread "main" java.lang.NoClassDefFoundError: weblogic/kernel/KernelStatus 
    at weblogic.jndi.Environment.,clinit9(Environment.java:78) 
    at weblogic.judi.WLInitialContextFactory.getInitialContext(WLInitialContextFactory.java:117) 
    at javax.naming spi NamingManager.getInitialContext(NamingManager.java:667) 
    at javax.naming InitialContext.getDefaultInitCtx(InitialContext.java:288) 
    at javax.naming.InitialContext.init(InitialContext.java:223) 
    at javax.naming InitialContext.einit,(InitialContext.java:197) 
    at com.MessageGenerator.getInitialContext(MessageGenerator.java:42)