Thursday, February 04, 2016

How to format an external hard disk or USB disk whose size is > 32GB as FAT32 ?

Formatting an external disk or usb disk of size more than 32 GB is a problem ? Then use the this tool available at below link. with this tool you can format the disk of size 2TB.

How to create local RHEL DVD repository for package installations ?

This blog tells you how to create a local repository from a RHEL installer DVD iso image.

Firstly please note that  RHEL is not a free software.  To get access to the fully up-to-date repositories (RHN) a  paid subscription is required.Without this subscription it will not be possible to get security updates and the newest versions of packages. An alternative for using RHEL would be CentOSor Scientific Linux. Both are free and almost identical to RHEL. The below steps should only be used for testing, studying or evaluation purposes. The steps below are based on RHEL server 6.4 but the basics are the same for other versions.

Pre Conditions prior performing the following setup steps.
- RHEL installed system,
- ~4-8 GB free space on disk.

All the below steps are to be executed with root privileges.

1. A directory needs to be created which will contain the repository with following command:
    $ mkdir /mnt/rhel_repo

2. Mount the DVD disk or iso image with following command.
    $ mount /dev/dvd /media
    If an image is used instead of a DVD you can mount it as follows (with following command):
    $ mount -o loop /path/to/rhel.6.4.iso /media

3. Copy the contents from the DVD to the newly created directory with following command:
    $ cp -ar /media/. /mnt/rhel_repo/

4. Set up the system to use the freshly created repository with following command:
    $ cd /etc/yum.repos.d/
    $ rm *.repo
    $ vi rhel64dvd.repo

    # add the following information:

     name=Red Hat Enterprise Linux - DVD Server Repository

     name=Red Hat Enterprise Linux - DVD Load Balancer Repository

      name=Red Hat Enterprise Linux - DVD High Availability Repository

5.  Disable RHN and activate DVD repository:
      $ vi /etc/yum/pluginconf.d/rhnplugin.conf
      # make sure enabled is set to 0 (enabled = 0)

6. Now run the following command in Terminal.
    $ yum clean all

    Loaded plugins: product-id, security, subscription-manager
    This system is not registered to Red Hat Subscription Management. You can use subscription-             manager to register.
    Cleaning repos: rhel-dvd-ha rhel-dvd-lb rhel-dvd-server
    Cleaning up Everything

    $ rpm --import /mnt/rhel_6.4_dvd/RPM-GPG-KEY-redhat-release

5. Now following yum update command to update the yum repositories.

    $ yum update
    Output :
    Loaded plugins: product-id, security, subscription-manager
   This system is not registered to Red Hat Subscription Management. You can use subscription-             manager to register.
    Setting up Update Process
    No Packages marked for Update

    From this point on you can use yum to search, install and remove packages that are available on         the local system.

    The following message will still be visible but it can be ignored.
    This system is not registered to Red Hat Subscription Management.

Wednesday, February 03, 2016

How to decrypt the Filevault encrypted volume using Recovery HD ?

There might be a time where you want decrypt the FileVault encrypted mac, but you are facing issues in logging into Mac to perform decryption using system preferences. In such cases the following steps will help you in decrypting the disk using Recovery HD.
  1. Reboot the Mac, Go to recovery HD partition of the system. (To start your computer from Recovery, restart your Mac and hold down the Command and R keys at startup.)
  2. Open Terminal application from Utilities -> Application. 
  3. First will need to identify the Logical Volume UUID of the encrypted drive using the diskutil corestorage list command:
          diskutil corestorage list 

      4.  Once you have the UUID of the logical volume as shown in above picture, you can then either             unlock or decrypt the encrypted volume using the following commands.

      a) Using the password of an authorised account or the recovery key ( Provided by the                                FileVault at the time of enabling it) on the command line
           To unlock: diskutil corestorage unlockVolume UUID –stdinpassphrase  

           The -stdinpassphrase flag will cause the command to prompt you for the password/passphrase
          of an account that’s authorised to unlock the encryption or the recovery key for the system. If              successful, the drive will unlock and mount.

      5.   Once we have unlocked the disk, we can now decrypt the volume.
            To decrypt: diskutil corestorage revert UUID –stdinpassphrase  

          You’ll be prompted for the password/passphrase of an account that’s authorised to unlock the              encryption or the recovery key. Once provided, decryption of the encrypted volume will                      begin. To track its progress, you can use the diskutil corestorage list command. Once the drive            has been completely decrypted, it will no longer be listed as a CoreStorage volume by diskutil            corestorage list. In Disk Utility, it will appear as a normal hard drive.  

      6.   Reboot the mac , It is now no longer encrypted with FileVault.


Wednesday, January 27, 2016

How and where can i reverse lookup the MD5 or SHA1 hashes or generate these hashes ?

         If you are looking for tool which reverse looks up a database to find out what text created your hash value or you want to check which generates those md5 or sha-1 etc hashes, then there is online website available here which does the job pretty neatly for you.

Tuesday, January 26, 2016

How PhET interactive simulations tool helps in building the knowledge of basic science in students

PhET Interactive Simulations, a project at the University of Colorado Boulder, is a non-profit[1] open educational resource (OER) project founded in 2002 by Nobel Laureate Carl Wieman. PhET began with Wieman’s vision to improve the way science is taught and learned. Their stated mission is "To advance science and math literacy and education worldwide through free interactive simulations."

PhET provides fun, free, interactive, research-based science and mathematics simulations. These tests include student interviews and observation of simulation use in classrooms. The simulations are written in Java, Flash or HTML5, and can be run online or downloaded to your computer. All simulations are open source 

Following video explains what is PhET. The PhET simulation software is available for Windows, Linux and Mac platforms. The PhET simulators for the appropriate platforms can be downloaded from here