• Failed to send 300 byte long packet over fallback interface

    1.0 Error

    While configuring a server, the following errors were noted in the logfiles.

    send_packet: Operation not permitted
    dhclient.c:2386: Failed to send 300 byte long packet over fallback interface.
    DHCPREQUEST on eth0  port 67 (xid=0x1580bfd0)

    2.0 Solution

    There are two possibilities depending upon whether DHCP is being used for getting the network IP address or not.

    2.1 ...

  • Dovecot: imap Error: open (/var/mail/username) failed


    While configuring mail on a Ubuntu Linux server running the Postfix mail server and Dovecot IMAP server, the following errors were observed in the mail log files,

    dovecot: imap(user1): Error: open(/var/mail/user1) failed: Permission denied (euid=1002(user1) egid=1002(user1) missing +w perm: /var/mail, we're not in ...
  • Not able to access files on Android device in Nautilus from Linux desktop

    1.0 Error

    After connecting an Android based phone with a Linux desktop using the USB cable, the files on the device are not shown by the Nautilus file manager. After clicking the tab for the device, an empty screen is displayed.

    Empty screen displayed after opening the device tab in ...</div></li><li><a href=Recaptcha: Error for site owner

    1.0 Error


    The login form for a Drupal based site had the username, password and recaptcha fields. However, instead of showing the image and input box, recaptcha displayed ERROR for site owner, Invalid domain for site key. Thus, it became impossible to login to the site. This effectively locked access to the administration ...

  • Android: AdbCommandRejectedException getting properties for device


    From Android Studio, the connection to the device for debugging was not getting established. The ADB logs gave the repeated error,

    PropertyFetcher: AdbCommandRejectedException getting properties for device ????????????: insufficient permissions for device


    1. As described in the documentation, Using Hardware Devices, a file /etc/udev/rules.d/51-android.rules was created.
    2. Using the
    3. Error while loading shared libraries: libz.so.1


      While building an Android app project under Studio, the build process terminated with the error,

      /home/user1/Android/Sdk/build-tools/22.0.1/zipalign: error while loading shared libraries: libz.so.1: cannot open shared object file: No such file or directory
      Error:Execution failed for task ':app:zipalignDebug'.
      > Process 'command '/home/user1/Android/Sdk/build-tools/22.0.1/zipalign'' finished with non-zero exit value 127


      The problem was resolved by installing the

    4. Unable to establish a connection to adb

      1.0 Problem

      After opening an Android project in Studio running under Ubuntu 15.04 Linux, the following error was displayed,

      Unable to establish a connection to adb. This usually happens if you have an incompatible version of adb running already. Try reopening Studio after killing any existing adb daemon.

      2.0 ...

    5. Invalid Gradle JDK configuration found

      1.0 Problem

      After starting Android studio, running on Ubuntu 15.04 Linux, the following error was reported:

      Invalid Gradle JDK configuration found. Open Gradle Settings. Platform SDK does not point to valid SDK (/usr/lib/jvm/jdk1.8.0_40).

      2.0 Solution

      The problem was solved by clicking in Android Studio, File -> Project Structure -> SDK Location. Under JDK location, enter the ...

    6. Using Git

      1.0 Introduction

      Git commands for common source code management use cases are listed.

      2.0 Install Git

      On an Ubuntu Linux system, Git can be installed with the command,

      $ sudo apt-get install git

      3.0 Set Identity

      Before using Git, the user's identity (name, email) has to be set

      $ git config --global user.email ...
    7. Importing an Android Studio project in Git

      1.0 Introduction

      Importing an Android Studio project into Git is easy. First create the project or import an existing project in Android Studio. In this case a placeholder project HelloWorld was created. The directory listing of the project root directory looks like this.

      $ ls -lsa
      total 60
      4 drwxrwxr-x ...
    8. Bash idioms

      bash idioms are tiny scripts, mostly one-liners, that accomplish a lot and can be used as building blocks in bigger scripts.

      1.0 Find most frequent words

      Suppose we have a bunch of text files and we wish to find the most frequently used words in those files, we can do that with the command,

    9. Posting images on Twitter

      It is fun posting images on Twitter but we often see that only a part of the image is visible in the stream of tweets. One has to click on the visible part to see the full picture. How to ensure that the full image becomes visible in the tweet stream? The answer lies in ...

    10. Getting WordPress to work with Varnish 4.0

      With Varnish 4.0, the VCL has changed. So an update from Varnish 3 .0 to Varnish 4.0 requires a change in the VCL file, /etc/varnish/default.vcl. As a part of Varnish cache server configuration for a WordPress based site, using nginx web server, the following VCL is ...

    11. Drupal: Web page stuck in maintenance mode


      After a Drupal based site came out of the maintenance mode, one particular web page was found to be stuck in the maintenance mode. It showed the message that the site was under maintenance, while the other web pages were displayed correctly.


      The problem was resolved by clearing the cache. In the administrative menu, the Flush ...

    12. nginx 502 Bad Gateway Error


      A routine software update on the server running nginx was done. After that the website stopped opening in the browser window and 502 Bad Gateway error along with the nginx version number was displayed. Looking in the log file showed an entry like,

      2014/06/26 11:09:53  2539#0: *15 connect() to ...