Interview Questions : Linux/Unix : Part - 4

1) What is piping?

Piping, represented by the pipe character “|”, is used to combine two or more commands together. The output of the first command serves as input the next command, and so on.

2) What is a superuser?

A superuser is a special type user who has open access to all files and commands on a system. Note that the superuser’s login is usually root, and is protected by a so-called root password.

Data Modeling - Conceptual, Logical, And Physical Data Models

The three level of data modeling, conceptual data model, logical data model, and physical data model, were discussed in prior sections. Here we compare these three types of data models. The table below compares the different features: 

SSH Login without Password in Nix

You want to use Linux/AIX/Unix and OpenSSH to atomize your tasks. Therefore you need an automatic login from hostA as user a to hostB as the same user. You don’t want to enter any passwords, because (for example) you want to call ssh from a within a shell script.

First log in on hostA as user a and generate a pair of authentication keys. Do not enter a passphrase:

Enable NLS Support in IBM Information Server (Datastage) 8.1 after its installed

This process describes how to enable NLS Support in IBM Information Server (Datastage) 8.1 after its installed with the NLS disabled option. This avoids the need to uninstall and reinstall datastage with NLS enabled.

1. Stop the DS Engine.

# cd /IBM InformationServer/Server/DSEngine

Dimensional Data Model

Dimensional data model is most often used in data warehousing systems. This is different from the 3rd normal form, commonly used for transactional (OLTP) type systems. As you can imagine, the same data would then be stored differently in a dimensional model than in a 3rd normal form model.
To understand dimensional data modeling, let's define some of the terms commonly used in this type of modeling:

Useful Perl Scripts : Part-1

1.   To Replace a character in a string

#!/usr/bin/perl

my $string = "This is string";

$string =~ tr/s/a/;

print $string;

Something about CRON in Nix

cron is a Nix utility that allows tasks to be automatically run in the background at regular intervals by the cron daemon. These tasks are often termed as cron jobs in Nix.  Crontab (CRON TABle) is a file which contains the schedule of cron entries to be run and at specified times.

This document covers following aspects of Unix cron jobs

 Crontab Restrictions

 Crontab Commands

 Crontab file – syntax

 Crontab Example

 Crontab Environment

 Disable Email

 Generate log file for crontab activity

Creating the Virtual Machine on Windows and Sharing folder with Guest OS[Linux]

I am recommending the Oracle Virtual Box for hosting a guest OS.

1) Download and Install the VirtualBox

2) Install the respected VirtualBox Extension

you can download it from here

Configuring Oracle database connectivity in a parallel environment in DataStage

Configuring access to Oracle databases includes granting the appropriate access level to users.

Granting access to the Oracle parallel server

To access the Oracle parallel server (OPS), users must have SELECT access to the sys.gv_$instance and sys.v_$cache tables.

Configuring TeraData database connectivity in a parallel environment in DataStage

Installing the Teradata tools and utilities

You must install Teradata Tools and Utilities on all nodes that run parallel jobs. See the installation instructions supplied by Teradata for complete information.

Ensure that the Teradata Parallel Transporter is installed and that the following environment variables are set in the /etc/profile file:

Unable to use Information Server due to expired passwords for WAS, xmeta or isadmin users

The following commands can be used to reset the passwords. Make sure to match these to your new passwords for the particular user. These commands should be run with the dsadm/isadmin user:

·          
                       

       Windows:

Replace the WAS administrator user/password:
<Info Server>\ASBServer\bin\AppServerAdmin.bat -was -user <new user name> -password <new password>

Interview Questions : Linux/Unix : Part-2

1: What are the 3 standard streams in Linux?

Output stream , represented as 0 , Input stream, represented as 1 and Error stream represented as 2.

2: I want to read all input to the command from file1 direct all output to file2 and error to file 3, how can I achieve this?

command <file1 0>file2 2>file3

Clear the Job log in MetaData Repository

Sometime having too much logs stored in the metadata repository can be a reason behind a jobs slow performance.

Periodic log clearance would not only improve the performance but would keep the metadata database healthy. 

Stopping and starting the DataStage server engine

Restart the IBM InfoSphere Information Server engine whenever you complete certain tasks such as editing the dsenv file on Linux or UNIX or modifying the uvconfig file.

• Unix :
  

1.    Log in to the engine tier computer as the IBM InfoSphere DataStage® administrator (typically dsadm).

2.    Change to the engine directory and set the environment.

3.  cd $DSHOME

. ./dsenv

DataStage Installation in Silent mode

To start the installation of IBM InfoSphere DataStage in silent mode:

1.    Log in with the administrator rights.

2.    Browse to the <InfoSphere Information server install_image_directory>/is-suite directory.

3.    Run the following command to start the installation program:

Starting and stopping WebSphere Application Server profiles

Starting a WebSphere Application Server profile

On Windows

To start a WebSphere Application Server profile, use any of these methods:

·         Go to Start > Programs > IBM WebSphere > Application Server V7.0 > Profiles > profile_name > Start the server.

·         Start the Windows service associated with the IBM WebSphere Application Server V7.0 profile.

·         Run this command: was_install_dir\bin\startServer.bat server1 –profileName profile

·         Run this command: profile_dir\bin\startServer.bat server1

Managing profiles on WebSphere Application Server V7

Listing WebSphere Application Server profiles

To list all profiles on a server:

• On Windows: was_install_dir\bin\manageprofiles.bat –listProfiles
• On UNIX/Linux:was_install_dir/bin/manageprofiles.sh –listProfiles

DataStage Error : Unable to connect with InfoSphere DataStage Clients

Problem
When connecting to InfoSphere DataStage one the following errors is received:

1. Failed to authenticate the current user against the selected Domain <Domain name>:
Could not locate the SecurityServer at host/port:/ to validate the userid and password entered. You may need to specify valid security ServerHost/Port in (WAS_INSTALL_ROOT)/properties/sas.client.props file.

DataStage Error: DSR.ADMIN Failed to write to project file.

Problem
Unable to delete a parameter from DataStage Administrator receive the error: DSR.ADMIN Failed to write to project file.

Receive the error DSR.ADMIN Failed to write to project file. trying to delete parameter from DataStage Administrator.

Saving InfoSphere DataStage settings files

In Linux and UNIX, for Version 7.5.3 and earlier, the engine directory is /user_home/Ascential/DataStage/DSEngine, where user_home is the home directory of the InfoSphere DataStage administrator who originally installed InfoSphere DataStage.

For Version 8.0.1 and later, the engine directory is /opt/IBM/InformationServer/Server/DSEngine. By default, this user is named dsadm. For Version 7.5.3 and earlier, each project is in its own directory in the /user_home/Ascential/DataStage/Projects directory.