Category Archives: Tips and Tricks

Jenkins Configuration Issue

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I was trying to setup Jenkins web app inside the Tomcat server and it continuously gave me this error:

SEVERE: Failed to initialize Jenkins
hudson.util.NoHomeDir

This I fixed by creating the folder ‘/usr/share/tomcat7/.jenkins’

mkdir /usr/share/tomcat7/.jenkins

On redeploying Jenkins I again noticed the following error.

WARNING: Failed to record boot attempts
java.io.FileNotFoundException: /usr/share/tomcat7/.jenkins/failed-boot-attempts.txt (Permission denied)

I fixed this issue by giving full access to this folder.

sudo chmod 777 /usr/share/tomcat7/.jenkins

I believe 777 is not a good approach in a production environment, but for development perspective it looks ok.

Completely removing packages in Debian Linux

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I recently had to find out if a particular package was properly installed in my Debian Linux OS as something was broken. I used the following command to do that.

dpkg --get-selections | grep -v deinstall | grep oracle

This basically lists out all the packages which contain the text ‘oracle’ in them. Once I find out the exact package name I can actually decide to remove all packages containing them.

sudo apt-get purge oracle*
sudo apt-get autoremove oracle*

Showing a running clock in a linux shell

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I was working with a scheduler and wanted to keep track of my server time. Continuous invocation of date command wouldn’t cut it. So a little search on net lead me to this link which basically sums up the following script. This script will show the current time on the top left corner of your terminal which is good enough for my usecase.


while sleep 1;do tput sc;tput cup 0 $(($(tput cols)-11));echo -e "\e[31m`date +%r`\e[39m";tput rc;done &

I executed this code on a Cent OS system and it worked fine. I have tested this snippet in Debian as well and it worked like a charm. This won’t solve everybody’s problem but for specific situation where you just want to watch the clock of your server from a shell this is a good enough script.

Synergy for Multi-Computer Control

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I have to work with Windows, Linux and Macbook environment and with time I have no issues working with all of these environments simultaneously. What used to irk me the most was the need to physically use multiple keyboards and mouse and control my Windows laptop and Macbook. Doing VNC / Remote Desktop into another computer didn’t cut it. So I found out about Synergy project long time ago. This is a free and open source keyboard/mouse sharing solution.

Basically the computer whose keyboard/mouse you want to use becomes the Synergy server and all other laptops / computer would become Synergy client. It is very easy to setup and once it is done I can use the keyboard / mouse of of my Macbook to control my windows laptop as well as Linux laptop simultaneously.

Detecting Java Processes listening on local ports

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We can use the jps command that is part of JDK to find out which Java processes are running in the current user’s session. We can further find out which network ports have been opened by a particular java process.

Use the follwing command to list all java processes:
jps -l

If you want more details about a process you can execute the following command:
jps -v | findstr <process id>

The following variant of netstat command lists all the listening as well as established socket connection in a system:
netstat -ano

This command can be further used to find out what sockets are opened by a specific process
netstat -ano | findstr <process id>

See hidden files in Mac OS Finder

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I like to see all the files in the project folder where I am working. So it is inconvenient not being able to see “.gitignore” and “.git” inside the folder where I have git repository. On a brief lookup of the internet I found this article which proposes two approach of making hidden files visible in finder.

Approach #1: Using Terminal

To show hidden files
defaults write com.apple.finder AppleShowAllFiles TRUE
killall Finder

To turn off showing of hidden files
defaults write com.apple.finder AppleShowAllFiles TRUE
killall Finder

Approach #2: Using an App
Funter is a small app which allows the user to toggle the hidden file visibility on and off at the click of a button which is quite convenient.

What I used?
I preferred the terminal approach as I am fairly comfortable with it and I didn’t want to add a new application into my mac’s start-up and menu bar.

How to find Linux distribution and kernel version

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In order find out what version of Linux you are running you can execute either of the following commands:

  • cat /etc/*-release
  • lsb_release -a
  • cat /proc/version
  • dmesg | head -1

To find out the kernel version of Linux you can execute either of the following commands:

  • uname -a
  • uname -mrs

Disclaimer: These commands worked for me on Debian Linux.

Update for Oracle Linux

The following commands gave accurate information about OS and release numbers on Oracle Linux.

rpm -qf /etc/redhat-release

oraclelinux-release-6Server-8.0.3.x86_64
cat /etc/issue.net | head -1

Oracle Linux Server release 6.8

 

Multi tabbed windows explorer

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In this world of multi-tabbed browsing I find it inconvenient that Windows Explorer has no multi tabbed support. I did some search and found out Clover. I downloaded and installed this tool and voila my Windows Explorer has got tabs. The tool itself is simple and integrates seamlessly with Windows Explorer in Windows 8. I have not had time to check it on my Windows 7 laptop, maybe sometime soon I will post an update.

Finding unread email in Android GMail Client

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Recently I noticed that my GMail inbox showed ‘0’ unread emails but my Android phone showed ‘1’ unread email persistently. I found the following trick which solved this problem. On my handset I clicked on ‘Search’ option and then typed the following in the search bar:

is:unread in:inbox

This allowed me to show only unread email in my Android Gmail client. Out Popped a one and half month old email which was still unread. All I had to do was open that email and the issue was gone.

What is not clear to me is how the GMail website showed 0 unread email while the Android client showed 1 unread email simultaneously for weeks at stretch. Perhaps the Android GMail client does a better job at keeping track if you missed reading a particular email a while back.

Open Command Window Here in Windows 7

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Being a hard core java programmer the Windows console is only one step away from me. In Windows 7 I use a nifty inbuilt feature which allows me to open a command window and switch to a given directory in a single step.

  • Using My Computer / Windows Explorer navigate to the relevant folder.
  • Press Shift and do a Right Click either on the folder name.
  • You will get a popup menu with the option “Open Command Window Here”.
  • Clicking on this option will open the console / terminal window with this folder as the current directory.
  • You can Right Click on an empty area as well to open the console/terminal for the current folder.

This facility is a time saver and I really like using it every now and then.