Connect to remote Oracle database server from RedHat Linux 7 using Oracle InstaClient

Hi friends,

I have come across a situation, where I need to connect to remote Oracle database server from RedHat Enterprise Linux (RHEL) 7. I found a way of using the Oracle InstaClient instead of installing the full Oracle DB which internally consists of Client.

Pre-requesites

1. Linux mahcine (I tried with RHEL 7) with following softwares
• Java (JAVA_HOME should be available)
• Development Tools (RHEL 7 tools like gcc etc.)
2. Another machine where Oracle server is installed with the following config
• Database schema should be available
• Users should be available instead of system/sysdba users
3. Both machines shall be reachable to each other via ping.

Note: You should know the database server SID/service name.

Procedure

Download

1. Download the insta client from Oracle Official Page
2. In my case, I have downloaded the "Instant Client for Linux x86-64"
3. Accept the license agreement
4. Click "oracle-instantclient18.3-basic-18.3.0.0.0-1.x86_64.rpm" to download
5. Optionally, you can download the "oracle-instantclient18.3-sqlplus-18.3.0.0.0-1.x86_64.rpm" to have sqlplus command line utility for testing
6. Alternatively, you can download the zip files and download the same to install.
7. In my case, I am going with RPMs.

Install

• Install the downloaded RPMs
• #> yum install oracle-instantclient18.3-basic-18.3.0.0.0-1.x86_64.rpm
• #> yum install oracle-instantclient18.3-sqlplus-18.3.0.0.0-1.x86_64.rpm
• While installing, it asks for locations, accept the defaults by pressing the "Enter" button

Note: If any dependencies are there, please install those.

Environment Variables

• Create a oracle_env.sh file and setup your variables
• #> gedit /etc/profile.d/oracle_env.sh

export ORACLE_HOME=/usr/lib/oracle//client/
export TNS_ADMIN=/usr/lib/oracle//client/
export PATH=$ORACLE_HOME/bin:$PATH
export LD_LIBRARY_PATH=$ORACLE_HOME/lib:$LD_LIBRARY_PATH

• Save your file
• Source your file with following command
• #> source /etc/profile.d/oracle_env.sh

tnsnames.ora

• Create tnsnames.ora file in your $ORACLE_HOME with following syntax

localsid = (DESCRIPTION =
    (ADDRESS = (PROTOCOL = TCP)(HOST = )(PORT = ))
    (CONNECT_DATA =
      (SID = )
    )
  )

• Instead of SID, you can use SERVICE_NAME also.

Connect

• You can test the connection
• #> sqlplus @

You should be able to connect to your remote database.

Hope, it is useful for you.

Please send your comments and feedback to psrdotcom@gmail.com

Completely uninstall openjdk in RedHat Enterprise Linux (RHEL)

Hi all,

Today, I'll explain how to uninstall completely the openjdk from the RedHat Enterprise Linux (RHEL) machine.

Some of the softwares requires only the Oracle Java and having the openjdk, sometimes causes an issue. So, some users wants to remove the openjdk from the linux machine.

Pre-requisites

• openjdk installed on the machine
• Check for java alternatives, when multiple java versions installed
• #> /usr/sbin/alternatives --config java
• Result with + is the currently selected java for the machine

Procedure

1. Find out the installed openjdk versions

#> rpm -qa | grep java
#> rpm -qa | grep jdk

Sample Output:

java-1.8.0-openjdk-1.8.0.191.b12-1.el7_6.x86_64

java-1.8.0-openjdk-headless-1.8.0.191.b12-1.el7_6.x86_64

2. Remove the all openjdk versions

#> yum remove <>

Example:
#> yum remove java-1.8.0-openjdk-1.8.0.191.b12-1.el7_6.x86_64

#> yum remove java-1.8.0-openjdk-headless-1.8.0.191.b12-1.el7_6.x86_64

Hope, it is useful for you to configure java on your linux machine.

Please send your feedback and comments to psrdotcom@gmail.com