Enable display of hidden files and folders in Mac

This article is note to myself. It lists the command to be executed to show hidden files and folder in Mac. As a practice, the names of the Hidden files and folders are prefixed with a period.

Step 1: Open the Terminal – type Cmd + Space followed by terminal in the search box and press return.

Step 2: Within the terminal window, enter the following command and press return.

defaults write com.apple.finder AppleShowAllFiles YES

If you would like to hide hiddens files and folders, type:

defaults write com.apple.finder AppleShowAllFiles NO

Step 3: Relaunch the Finder.

  • Hold the Option + Control keys and click on the Finder icon on the Dock.
  • Select Relaunch in the menu.

Find the version of the Linux distribution installed in your system

This post is a note to myself since I have come across the need of verifying the version of the Linux distribution installed on my system several times till date.

Method 1:

The standard technique I have been using till date to check the version of the Linux OS installed on my system was to execute: cat /etc/issue.

If you are using a customized version of the Linux based OS, the file, /etc/issue will probably display a custom message based on the OS distribution.

Method 2:

If you know that the Linux OS installed in your system is a variant of RHEL or Fedora, say CentOS, the command, cat /etc/redhat-release will provide the human readable release name of the installed OS followed by the version and the code name of the release.

If you are using other variants of the Linux OS, there is a high probability that the execution of the command, cat /etc/*-release may provide you with the necessary details.

Method 3:

If you are using a recent version of Linux distribution, the command: lsb_release -i -r will display the Distribution name (-i) and the Release number (-r).

On a side-note, if you are just looking for the version of the kernel and gcc that were used to build the release: cat /proc/version will provide the details.

1. http://serverfault.com/questions/89654/what-version-of-rhel-am-i-using
2. http://serverfault.com/questions/188037/how-do-i-determine-what-version-of-red-hat-enterprise-linux-my-server-is-running
3. http://www.cyberciti.biz/faq/find-linux-distribution-name-version-number/
4. http://unix.stackexchange.com/questions/124667/how-to-know-which-linux-and-which-version-i-am-using

Private Internet Access client fails to connect in OS X Yosemite

I have been using PIA as a VPN provider for some time now and have no complaints about the access speed. Setting up the PIA client on Windows was a breeze. Configuring OpenVPN to connect to PIA in my Ubuntu box was easy.

Few months ago, I switched over to a Macbook Pro. I downloaded the Mac OS X VPN client from the Client Support area of the PIA website and installed it successfully. But, when attempting to connect to one of their US VPN Tunnel Gateway, the connection did not go through and seamed frozen in the ‘connecting’ phase.

Few weeks zipped by the time I came across a solution listed at the PIA Discussion Forum.

The PIA blog post by dvh listed three alternatives to fix the problem:

  1. Configuring PIA client to use TCP on behalf of UDP.
  2. Disabling the OS firewall.
  3. Whitelist PIA executable in the Firewall settings.

I do not prefer using a TCP connection with the VPN tunnel as the three way handshake would slow down my connectivity.

It did not make sense lowering system security so as to connect to the VPN tunnel. Therefore, disabling OS firewall was not an acceptable choice.

The last option of adding PIA OpenVPN executable to the whitelisted applications in the Firewall settings made sense. I could implement the fix by following the below steps:

  • Open: System Preferences (Cmd+Space and Type: System Preferences)
  • Choose: Security and Privacy followed by Firewall on the tab-bar.
  • Click: + icon within the Firewall dialog box to add the PIA OpenVPN program to the whitelist. This executable is listed in /private/tmp folder and named pia_openvn.

On completion of the above steps, the PIA Mac client was able to connect to their gateway successfully.


How to fix the Tomcat 7 private instance and Eclipse integration error in Ubuntu

The first step as part of my journey in learning Spring MVC was to create a private instance of Tomcat 7. The procedure I had followed is documented as part of my earlier post: How to setup multiple instances of Tomcat 7 in Ubuntu.

The next step was to setup Eclipse to recognize the Tomcat 7 private instance.

A new server instance can be registered in Eclipse using Window -> preferences -> Server -> Runtime Environments menu.

But, when I try add the private Tomcat 7 instance, Eclipse reports that it could not identify the version of the Tomcat and refuses to register the instance.

Following the suggestions by David Edwards at askubuntu.com for a problem not directly linked to my problem, solved the Eclipse-Tomcat7-private-instance-integration issue.

The solution suggested by David Edwards was to create a link for the lib and bootstrap.jar library in the private instance folder.

Due to missing fix for the bug-297675 in the tomcat7-user package, the tomcat7-instance-create script fails to setup everything as required by Eclipse when executed.

The part of the solution that I followed can be divided into two steps.

Step 1: Create a link to the lib folder and the bootstrap.jar file located at /usr/share/tomcat7 in the tomcat7 private instance directory.

ln -s /usr/share/tomcat7/lib ~/Workspace/github/springapp/tomcat//lib
ln -s /usr/share/tomcat7/bin/bootstrap.jar ~/Workspace/github/springapp/tomcat/bin/bootstrap.jar

In addition, I also had to create a link to /usr/share/tomcat7/bin/tomcat-juli.jar.

ln -s /usr/share/tomcat7/bin/tomcat-juli.jar ~/Workspace/github/springapp/tomcat/bin/tomcat-juli.jar

Note: ~/Workspace/github/springapp/tomcat is my Tomcat 7 private instance folder created using tomcat7-intance-create script.

Step 2: Either download the catalina.policy file from code repository or from within the general Tomcat 7 instance configuration folder. For instance:

# If you opt for downloading the file - replace 'precise' with the right name of your Ubuntu release.
curl http://bazaar.launchpad.net/~ubuntu-branches/ubuntu/precise/tomcat7/precise/download/head:/catalina.policy-20110521092527-dk8tcyjy21h8eu9h-1652/catalina.policy > ~/Workspace/github/springapp/tomcat/conf/catalina.policy

Note: Make sure that you are downloading the latest version of http://bazaar.launchpad.net/~ubuntu-branches/ubuntu/precise/tomcat7/precise/view/head:/conf/catalina.policy file.

Eclipse should be able to recognize the version of Tomcat without issues.

Meanwhile, shutdown and restart the private instance using the commands:

settipalli@settipalli-ubuntu:~/Workspace/github/springapp/tomcat$ ./bin/shutdown.sh

# Followed by:
settipalli@settipalli-ubuntu:~/Workspace/github/springapp/tomcat$ ./bin/startup.sh

1.How to setup multiple instances of Tomcat 7 in Ubuntu
2.Unknown version of Tomcat was specified with tomcat-7.0.42
3.Tomcat and Eclipse Integration Error : “Unknown version of Tomcat was specified.”
4.Cannot start tomcat after installing a private instance
5.Tomcat 7 and Eclipse integration getting error
6.Configure TOMCAT in Eclipse
7.Eclipse Community Forums – Can’t add a new Tomcat 7 Server
8.Eclipse 4.2 (Juno) ‘Cannot create a server using the selected type’ in Tomcat 7
9.Eclipse can’t find catalina.policy and bootstrap.jar where it expects them
10.Man page of tomcat7-instance-create

How to fix blank screen issue while attempting to edit WordPress blog posts in distraction free writing mode in Ubuntu?

I like writing, though I write occasionally. WordPress.com has been my platform of choice for several years now. I used to use the Windows Live Writer to create and edit my blog posts in Windows. It is excellent editor by all angles. When using Ubuntu, I stick with the web-based text editor on WordPress.com.

Since the launch of Markdown support for WordPress.com web based editor(http://en.support.wordpress.com/markdown/), my dependency on the web-based editor increased multifold.

Recently, I was plagued by the ‘blank screen’ problem whenever I used to switch to the ‘distraction free mode’ while editing text from within the Text Editor on the Chrome browser.

Meanwhile, I encountered the same problem when launching https://web.whatsapp.com to use the WhatsApp web client from within the Chrome browser. The symptoms of the problem seemed alike. And the solution also worked.

The solution was to launch the Chrome browser with hardware based rendering disabled using the command:

settipalli@settipalli-ubuntu:~$ google-chrome --disable-gpu

The other blog post also provides details on creating a desktop shortcut for Chrome browser with GPU disabled.

1. How to fix the blank screen problem while launching WhatsApp web client from Google Chrome installed in Ubuntu
2. WordPress.com
3. Ubuntu 12.04.5 LTS (Precise Pangolin)
4. WordPress.com – Markdown
5. Write (More) Effortlessly With Markdown
6. WordPress.com – Writing and Editing – Editor
7. Markdown – Wikipedia
8. Download Windows Live Writer

How to fix the blank screen problem while launching WhatsApp web client from Google Chrome installed in Ubuntu

I have Ubuntu 12.04.5 LTS version installed on my Compaq Presario A900. Its a widescreen laptop (actually, a desktop replacement) with 17 inch display. I love the large screen and the full sized keyboard. Its such a pleasure to see Ubuntu run smoothly on this laptop.

Recently, WhatsApp launched their web-client with a limitation that it can only run on the Chrome web browser.

When I launched https://web.whatsapp.com on the Chrome browser, everything seemed fine. Scanned the QR code and found that my display went blank. No response for any keystrokes, mouse movements. The only way to recover was to put the system to sleep and wake-up. Upon wake-up, Unity would crash and unity-reset does not help. The only option was to issue a gracefull reboot from terminal (Ctrl-Alt-F1). The issue was reproducible consistently.

Initially, I felt this could be a display driver problem. Since the laptop contains an Intel Integrated Graphics Adapter, I verified if there are any new drivers listed on the HP website. Found everything was upto date with respect to Graphics adapter and related drivers.

The second step was to Google for a solution. There are numerous people who have reported ‘Blank Screen issue on Ubuntu 12.04 LTS’. Most of them were related to Screen Saver and some of them with respect to XOrg settings. None of the solutions helped.

Finally, with a hunch, I started reading about Google Chrome features and the steps to be followed to enable/disable experimental features. As part of this investigation, I came across an option to disable ‘GPU Hardware Rendering’. The option was --disable-gpu. This option turned off the hardware rending facility in the browser and restricted it to use ‘Software Renderers’. The quality of the output when hardware rendering is used, is usually superior, but in this case, I had to stick with software renderers.

settipalli@settipalli-ubuntu:~$ google-chrome --disable-gpu

Running Chrome with GPU rendering disabled solved the mystry behind blank screen. I was able to launch https://web.whatsapp.com perfectly without issues.

I decided to create a desktop shortcut for the Chrome with GPU disable switch turned on such that whenever I would like to use the WhatsApp web client, I do not accidently start the browser with hardware rendering enabled and be greeted with a blank screen.

The first step was to copy the exisitng google-chrome.desktop script located within the /usr/share/applications folder and name it, say, google-chrome-gpu-disabled.desktop. The contents of the script are listed below:

[Desktop Entry]
Name=Google Chrome - GPU Disabled
# Gnome and KDE 3 uses Comment.
Comment=Access the Internet
Exec=/usr/bin/google-chrome-stable --disable-gpu %U

[NewWindow Shortcut Group]
Name=New Window
Exec=/usr/bin/google-chrome-stable --disable-gpu 

[NewIncognito Shortcut Group]
Name=New Incognito Window
Exec=/usr/bin/google-chrome-stable --incognito --disable-gpu 

Now, whenever I search Chrome from within the Search bar in the Unity-Dashboard, I could see two Chrome icons, one with the GPU support, other without the GPU disabled.

1. WhatsApp web-client
2. Ubuntu 12.04.5 LTS (Precise Pangolin)
3. Compaq Presario A900 Notebook PC
4. WhatsApp Blog – WhatsApp Web
5. Chrome Browser – Google

How to setup multiple instances of Tomcat 7 in Ubuntu

I was trying to learn Spring MVC and was interested to setup a dedicated instance of Apache Tomcat 7 for the pet project rather than using the single installed instance. I used a Ubuntu 12.04 LTS desktop edition while performing the below steps.

Using a dedicated instance rather than a general instance would allow me load custom libraies and not tamper with the settings and libraries utilized by the general instance of Tomcat 7.

Step 1: Install the tomcat7-user package.

sudo apt-get install tomcat7-user

Step 2: Setup a parent folder where you would like to store the instance specific configuration and libraries

mkdir $HOME/Workspace/github/springapp

I have specified a path specific to my project folder. You can choose any folder of your choice.

Step 3: Use the tomcat7-instance-create command to create and configure the Tomcat 7 instance folder at $HOME/Workspace/github/springapp/tomcat.

tomcat7-instance-create $HOME/Workspace/github/springapp/tomcat

#       tomcat7-instance-create [OPTIONS] DIRECTORYNAME

The default port used by the instance would be 8080. If you would like have the new instance listen to a different port, use the -p switch. This is useful when you like to have both the general and the dedicated instance of Tomcat running simulataneously.

Similary, the -c switch allows us to specify a control port which can be used to send ‘Magic Words’ that cause Tomcat to trigger specific actions. For instance, the default magic word to gracefully shutdown Tomcat is SHUTDOWN and the default control port is 8005.

As an example, to have Tomcat listen on port 8085 with control port being 8010 and the Magic Word to shutdown Tomcat being TAKEYOURLOADOFF:

tomcat7-instance-create -p 8085 -c 8010 -w TAKEYOURLOADOFF $HOME/Workspace/github/springapp/tomcat

The output would be similar to:

You are about to create a Tomcat instance in directory '$HOME/Workspace/github/springapp/tomcat'
* New Tomcat instance created in $HOME/Workspace/github/springapp/tomcat
* You might want to edit default configuration in $HOME/Workspace/github/springapp/tomcat/conf
* Run $HOME/Workspace/github/springapp/tomcat/bin/startup.sh to start your Tomcat instance

Note: The variable $HOME would be replaced with the absolute path of the directory in your output.

To learn more about the options available for the tomcat7-instance-create command, please refer the man page:

[man tomcat7-instance-create][3]

Step 4: Start the new instance of Tomcat 7.

settipalli@settipalli-ubuntu:~/Workspace/github/springapp$ tomcat/bin/startup.sh
Using CATALINA_BASE:   $HOME/Workspace/github/springapp/tomcat
Using CATALINA_HOME:   /usr/share/tomcat7
Using CATALINA_TMPDIR: $HOME/Workspace/github/springapp/tomcat/temp
Using JRE_HOME:        /usr
Using CLASSPATH:       /usr/share/tomcat7/bin/bootstrap.jar:/usr/share/tomcat7/bin/tomcat-juli.jar
Tomcat started

Step 5: To verify if the new instance of Tomcat has loaded successfully, navigate to ‘localhost:8085‘ in your web-browser. You would be greeted with an empty page. This is normal.

To confirm if Tomcat has started and is listening on the specific ports, execute the below command.

settipalli@settipalli-ubuntu:~/Workspace/github/springapp$ netstat -punta | grep java
(Not all processes could be identified, non-owned process info
 will not be shown, you would have to be root to see it all.)
tcp6       0      0 :::8085                 :::*                    LISTEN      4862/java
tcp6       0      0          :::*                    LISTEN      4862/java

To reconfirm if everthing is fine, look into the logs at: $HOME/Workspace/github/springapp/tomcat/logs/localhost_access_log..txt. The content should be similar to: - - [30/Jan/2015:04:03:55 +0530] "GET / HTTP/1.1" 404 - - - [30/Jan/2015:04:03:56 +0530] "GET /favicon.ico HTTP/1.1" 404 -

Since we have not configured any web-apps to be servered by Tomcat, 404 response is valid.

Similary, review $HOME/Workspace/github/springapp/tomcat/logs/catalina.out for Tomcat startup messages.

To shutdown the instance, use the below command:

settipalli@settipalli-ubuntu:~/Workspace/github/springapp$ tomcat/bin/shutdown.sh

# Sample Output of the command
Using CATALINA_BASE:   /home/settipalli/Workspace/github/springapp/tomcat
Using CATALINA_HOME:   /usr/share/tomcat7
Using CATALINA_TMPDIR: /home/settipalli/Workspace/github/springapp/tomcat/temp
Using JRE_HOME:        /usr
Using CLASSPATH:       /usr/share/tomcat7/bin/bootstrap.jar:/usr/share/tomcat7/bin/tomcat-juli.jar
Jan 30, 2015 4:11:31 AM org.apache.catalina.startup.ClassLoaderFactory validateFile
WARNING: Problem with directory [/var/lib/tomcat7/common/classes], exists: [false], isDirectory: [false], canRead: [false]
Jan 30, 2015 4:11:31 AM org.apache.catalina.startup.ClassLoaderFactory validateFile
WARNING: Problem with directory [/var/lib/tomcat7/common], exists: [false], isDirectory: [false], canRead: [false]
Jan 30, 2015 4:11:31 AM org.apache.catalina.startup.ClassLoaderFactory validateFile
WARNING: Problem with directory [/var/lib/tomcat7/server/classes], exists: [false], isDirectory: [false], canRead: [false]
Jan 30, 2015 4:11:31 AM org.apache.catalina.startup.ClassLoaderFactory validateFile
WARNING: Problem with directory [/var/lib/tomcat7/server], exists: [false], isDirectory: [false], canRead: [false]
Jan 30, 2015 4:11:31 AM org.apache.catalina.startup.ClassLoaderFactory validateFile
WARNING: Problem with directory [/var/lib/tomcat7/shared/classes], exists: [false], isDirectory: [false], canRead: [false]
Jan 30, 2015 4:11:31 AM org.apache.catalina.startup.ClassLoaderFactory validateFile
WARNING: Problem with directory [/var/lib/tomcat7/shared], exists: [false], isDirectory: [false], canRead: [false]
Tomcat stopped

1. Add another instance of Tomcat, on Ubuntu
2. How to install Multiple instances of tomcat on a single ubuntu server
3. tomcat7-instance-create – Gists – GitHub
4. Ubuntu 12.04.5 LTS (Precise Pangolin)
5. Man page of tomcat7-instance-create