How to Create Index Partitions to Ranged Partitioned Table
Starting with Oracle 8, Oracle allows for tables to be divided into different storage areas called partitions. Each …
Articles
How to Move Partition Online in Oracle 12c
Starting 12c, Oracle has introduced a new feature for online movement of partitions. In this post we will discuss this …
How to Add or Modify Printer Settings in CentOS/RHEL Using GUI
Add a printer to system Start the printing configure application. Click the “Applications” on the panel, then go to …
What Is Machine-Id in Linux
The /etc/machine-id file contains the unique machine ID of the local system that is set during installation. The machine …
Java Interview Questions - Access Specifier
1. What are the access specifiers present in java? There are four types of access specifier present in java I,e public, …
Java Interview Questions - Applet
1. What is Applet? It is a special type of program that is embedded in the webpage to generate the dynamic content.
Java Interview Questions - Array
1. What is array and what is the use? Array is a collection of similar types of elements that have continuous memory …
Java Interview Questions - AWT
1. What is the difference between the paint() and repaint() methods? You should call this method if you want a component …
Java Interview Questions - Basics
1. Does garbage collection guarantee that a program will not run out of memory? Garbage collection does not guarantee …
Java Interview Questions - Control Structure
1. What are the controls structures present in java? Java supports five type of control structure. Conditional control …
Java Interview Questions - Exception
1. What is Exception and why to use? Exception is nothing but a situation where program terminate abnormally. 2. What is …
Java Interview Questions - File or Java.io Package
1. What is File? File is a container which store text or binary information for a permanent period. 2. What are the …
Java Interview Questions - Inheritance
1. How to access the member of a different class? To access the member of different class user may use Aggregation or …
Java Interview Questions - Java.util Package
1. Define package? package is a collection of group of similar types of classes , interfaces and sub packages. 2. State …
Java Interview Questions - Method
1. What are the different types of methods in java? There are 6 types of method support by java. They are:
Java Interview Questions - Multithreading
1. What is Thread from java point of view? Thread is a light weight sub process which is suitable for game & network …
Java Interview Questions - Nested Class
1. What is Nested top-level class? A top level class does not appear inside another class or interface. If a type is not …
Java Interview Questions - Operator
1. How may number of operators present in java? Java supports 44 number of of operator. 2. How to convert one type to …
Java Interview Questions - Package
1. What is package? Package is a collection of group of similar types of classes, interfaces and sub packages. 2. State …
Java Interview Questions - Polymorphism
1. What is Polymorphism and ways to supports in java? Polymorphism is the concept of “one interface and many …
Java Interview Questions - String & StringBuffer
1. What is String and how String differ from C Lang? String is a predefined class present in java.lang package. String …
Java Interview Questions - Swing
1. What is the difference between Swing and AWT components? Basically AWT came first and is a set of heavyweight UI …
Java Interview Questions - Variables and Block
1. What is variable? A variable is a container that holds values that are used in a Java program. Every variable must be …
Java Interview Questions - Collection
1. What is Collection and what is the difference between Collection and Collections? Collection is a group of similar …
Java Interview Questions - Constructor and Object
1. What is constructor and its types? Constructor a special type of method that is used to initialize the state of an …
Kernel:err: CIFS VFS: Cifs_mount Failed W/Return Code = -115
The Problem When mounting a remote CIFS shared volume, the following error is shown and the volume is not mounted:
Java: Ordered vs Sorted Collection
A collection is a group of objects contained in a single object. The Java Collections Framework is a set of classes in …
"Yum Clean" Command Examples in CentOS/RHEL/Fedora
During its typical operation, YUM will create a cache of metadata and packages that can be found at /var/cache/yum. …
How to Check Whether SELinux Is Enabled or Not?
Security-Enhanced Linux (SELinux) brings additional security measures to your Linux system to further protect its …
What Is New in Oracle 11gR2 Relink
Methods to relink all binaries Oracle 11gR2 has two methods of relinking all product binaries in a home. 1. Traditional …
Unable to Create Shared Memory Segment ORA-27125 While Starting Database
The Problem The host ran out of disk space and ASM and the RDBMS were unable to create audit files. The environment was …
PL/SQL Script to Find VARCHAR2 Values That Cannot Be Converted to Number
This script contains a PL/SQL block to find VARCHAR2 values that cannot be converted to a number. It can be used to help …
The SQL Server Operating System (SQLOS)
The SQL Server Operating System (SQLOS) is a separate application layer at the lowest level of the SQL Server Database …
Compound Trigger Example in Oracle
The compound trigger is a new trigger that has been introduced in 11gR1. The compound trigger makes it easier to program …
Manage Linux Processes and Services
Process Definitions The following terms are used to describe Linux processes: Program: A structured set of commands …
Exadata Interview Questions - Smart Scan
What is Smart Scan? The data search and retrieval processing can be offloaded to the Exadata Storage Servers. This …
ORA-39142: Incompatible Version Number 5.1 in Dump File
The Problem Trying to export schema/tables from higher Database version 12.2.0.1.0 and import to version 12.1.0.1.0, …
How to Move /Usr Directory Contents to a Separate LVM Logical Volume
This post describes how to move the contents of /usr directory to a separate LVM Logical Volume (LV). In the following …
Firewall-Cmd Command Examples in Linux
The firewall-cmd command enables you to configure firewalld by querying, adding, modifying, and deleting zones and …
How to Call Linux Script Program in Wlst Script
Linux Script: $ cat test.sh echo "HELLO WORLD" wlst script part: $ cat monitor_jdbc.py import os …
Example of Specifying an INDEX Hint in Oracle
The format for an index hint is: select /*+ index(TABLE_NAME INDEX_NAME) */ col1... There are a number of rules that …
How Can We Have Different RMAN Retention Policies for Different Backups
We cannot have different retention policies for different backups. The retention policy is always the same for all …
Index Skip Scan Hint Usage in Oracle Database
Index skip scans improve index scans against non-prefix columns since it is often faster to scan index blocks than …
OCFS2 Interview Questions
How do I get started? Download and install the module and tools rpms. Create cluster.conf and propagate to all nodes. …
Siebel Order Management - Promotions - Interview Questions
On which quote or order line items can a promotion be applied? Bundle Promotions can be applied to root product line …
How to Create Reference Partitioning in Oracle 11g (Example)
The TEST1 table will be the parent and therefore must be created as a partitioned table.And table TEST_TAB will be the …
How to Use ASMCA in Silent Mode to Configure ASM for a Stand-Alone Server
Oracle ASM Configuration Assistant (ASMCA) was introduced in Oracle ASM version 11.2. ASMCA supports installing and …
Reference Partitioning in Oracle Database
Reference partitioning provides the ability to partition a table based on the partitioning scheme of the table …
Composite Data Types in PL/SQL - Records and Collections
Composite Data Types You learned that variables of the scalar data type can hold only one value, whereas variables of …
How to Configure or Re-Configure Grid Infrastructure in Oracle 11gR2, 12cR1 and 12cR2
This post explains 11gR2 and 12cR1 Grid Infrastructure configuration framework config.sh(config.bat on Windows) which is …
Oracle 19c New Feature - Hint Usage Reporting
Hint Usage Report is a new feature from 19c which helps to determine from the execution plan output which are all the …
How to Restore Oracle Optimizer Statistics
Beginning with Oracle10G, when statistics are gathered for a table, the old statistics are retained so should there be …
Oracle Database OPatch and OUI Logs Location
Question: How to find the log files for OPatch and OUI ( Oracle Universal Installer)? OPatch (Common for Windows and …
Oracle SQL Script to Show Objects That Are Missing Statistics
This script shows which tables and indexes are either missing statistics or have stale statistics, and the statistics …
New Features for Oracle 11gR2 Relinking
This is a small note for the new features introduced in Oracle 11g related to Relinking. Methods of Relinking Oracle …
What Is ODBC? How Does ODBC Work?
Open Database Connectivity (ODBC) provides a standard interface that allows application access to many different …
Understanding PL/SQL Blocks
Block Types A PL/SQL program comprises one or more blocks. These blocks can be entirely separate or nested within …
"Communication Error With the OPMN Server Local Port" When Starting OPMN
The Problem When attempting to start the OPMN services the following error occurs: opmnctl: starting opmn and all …
How to Check and Set Max Size of PDB Storage
You can specify the maximum size for any PDB database using STORAGE clause in CREATE PLUGGABLE DATABASE command. If we …
How to Shrink the Datafile of Temporary Tablespace in Oracle
The database has a program that performs a huge sort operation (e.g. end of the year reporting process). This may cause …
Queries to Find Information and Work With Oracle Container Database (CDB) and Pluggable Database (PDB)
This post lists out different administrative tasks you can perform in a container database (CDB) and pluggable database …
How to Shrink a Temporary Tablespace in Oracle
Question: How to resize the TEMPFILE(s) for a temporary tablespace after they have grown larger than needed? Large sort …
Temporary Tablespaces Group in Oracle
This post explains why and how to create groups of temporary tablespaces. Grouping temporary tablespaces within a single …
UNIX/Linux: Finding Out Who Is Logged In
The who command shows you: Who is logged in Where users are logged in The who command has three forms.
Java Type Casting Basics
In this post, you will learn to: State the two types of type casting. Describe implicit type casting. Describe explicit …
How to Use Comments in Java
Single-line Comments Comments help easy understanding of code. A single-line comment is used to document the …
Lsof Command Examples in Linux
The lsof command prints a list of all files that are currently opened to all active processes. This can include …
Rpm Command Examples in Linux
The rpm command is used to manage RPM packages on Red Hat-derived distributions. It includes many different options, …
Grep Command Examples in Linux
The grep command, in its most basic form, is a search tool. Unlike find or locate, it is not limited to finding file …
Ls Command Examples in Linux
At some point in time, you must have used the ls command if you use UNIX/Linux systems. ls is the most commonly used …
Chattr Command Examples in Linux
The chattr command is used to change the attributes of a file or directory. The below table describes some of the …
Chmod Command Examples in Linux
The chmod command enables you to modify the permissions of a file or directory. Only the owner of the file or directory …
Understanding User Profile Files in Linux - .Bashrc, .Bash_profile, /Etc/Profile, /Etc/Bashrc
User profiles Individual users have personal habits and preferences for their Linux work environment, and so a variety …
How to Set and Change Special Permissions in Linux
Special permissions on files and directories in linux are : SetUID, SetGID and Sticky bit. With the help of “chmod” …
Bitwise Operators in C
We know that computers operate on one byte at a time i.e. 8 bits of data a manipulated as one unit.
C Pointers and Functions
Pointers and functions get on very well. Whenever data is to be passed to a function, especially large amounts of them, …
C Preprocessors
This is one of the special features available in C, but not found in many other languages. The preprocessor is a part of …
C Linked Lists
The concept of linked lists is one of the powerful features in C. It will also bring to you some of the powerful …
C Pointers - Definition and Operation Pointers & Structures
Pointers are one of the very powerful & special features of C. It simply means instead of using a variable name, you …
How to Move a Datafile to a Different Location on Physical Standby Database
Sometimes it is necessary to move a Datafile to another Location (eg. Mountpoint, ASM Diskgroup, etc.) due to Space …
How to Restore and Recover Single or Multiple Datafiles From a PDB Database
The Setup We will be using below setup for the purpose of this post: CDB name:CDB1 PDB name: pdbtest CDB1 …
How to Setup Transparent Data Encryption (TDE) in Oracle 12c for Non-Pluggable Database
TDE was introduced as of 10gR2 ( 10.2.0.1 ). In 12c TDE provides a completely different interface to manage the wallet …
How to Roll Forward a Physical Standby Using Recover From Service Command in Data Guard 12c
Rolling Forward a Physical Standby Database Using the RECOVER FROM SERVICE Command A standby database is a …
Oracle 12c Data Pump New Features
This post provides an Overview of all Data Pump related New Features of the Oracle Database 12.2 Release. Oracle Data …
Oracle 12c DataPump EXPORT (EXPDP) and IMPORT (IMPDP) New Features
Audit all expdp/impdp operations with unified auditing You can perform auditing on Data Pump jobs in order to monitor …
How to Create Backupdba, Dgdba and Kmdba Groups After the 12c, 18c and 19c Binary Installation
Users in the OSDBA group are granted the SYSDBA administrative privilege. Similarly, the OSOPER group is used to grant …
How to Rename a Datafile in the Primary Database and Manually Propagate the Changes to the Standby Database
When you rename one or more datafiles in the primary database, the change is not propagated to the standby database, …
How to Roll Forward Physical Standby Using RMAN Incremental Backup in Oracle 18c
For the purposes of this post, the following environment is used as an example to describe the procedure: Standby Name: …
How to Change Mac Address on Linux Temporarily
Whats a MAC address? A MAC address is a physical way of addressing your network card at a hardware level.
How to Change the Hostname on Ubuntu Server
Your hostname is a label that is assigned to your computer so that it can be identified. There are only a couple of …
How to Use the Ping Command in Linux
Ping is a program that is used to test the reachability of a host. It also measures the time it takes to send the packet …
How to Install Raspian on the Raspberry Pi
There are lots of different ways of installing Raspian to an sd card like win32diskimager and usb image writer but an …
How to Use Apt-Get on Debian or Ubuntu Systems
The advanced package tool, also known as APT is a tool that is used for the easy installation, removal and upgrading of …
How to Check the Apache Tomcat and Apache Httpd Version in Linux
Tomcat versions can be obtained by version.sh in bin directory of TOMCAT_HOME. HTTPD component version can be viewed …
Configure Systemd Service to Continue to Run When the User Session Ends (CentOS/RHEL 8)
Question: When a user logs out of their session any service they’ve started using the systemd user process is …
What Is Sticky Bit in Linux
A directory whose sticky bit is set becomes an append-only directory, or, more accurately, a directory in which the …
Unable to Mount Samba Share When FIPS Is Enabled
The Problem Unable to mount Samba share. Attempting to create a mount for a samba share fails. However is accessible …
What Are Oracle Data Guard Protection Modes and How to Configure Them
Data Protection Modes and Redo Transport When you define a redo transport mode, you are configuring the shipment of log …
How to Identify Which Volume Group Is Active in LVM
The way to check the status of VG is: lvs or lvdisplay. vgchange performs operation on underline LV, it activates or …
Monitoring a Data Guard Broker Configuration Using Enterprise Manager Cloud Control
Enterprise Manager Cloud Control provides a graphical user interface for monitoring the Data Guard configuration. The …
Beginners Guide to Multitenant Architecture and RAC
Non-CDB Architecture In Oracle Database 12c, there are two possible configurations, non-CDB and multitenant container …
Beginners Gude to Oracle RAC One Node
Oracle RAC One Node Oracle RAC One Node is a single instance of an Oracle RAC-enabled database running on one node in …
Configuring Transparent Application Failover (TAF) in Oracle RAC
Transparent Application Failover: Overview TAF is a runtime feature of the OCI driver. It enables your application to …
Beginners Guide to RAC Database Monitoring and Tuning
CPU and Wait Time Tuning Dimensions When tuning your system, it is important that you compare the CPU time with the wait …
Managing Backup and Recovery for Oracle RAC
Instance Recovery and RAC When an instance fails and the failure is detected by another instance, the second instance …
Beginners Guide to Upgrading and Patching Oracle RAC
Patch and Patch Set: Overview Oracle issues product fixes for its software called patches. They are associated with …
How to Modify Initialization Parameters in a Oracle RAC Environment
RAC Initialization Parameter Files When you create the database, Oracle Database creates an SPFILE in the file location …
Oracle RAC 12c Administration Using Enterprise Manager
Enterprise Manager Cloud Control Cluster Database Home Page The Enterprise Manager Cloud Control (EMCC) Cluster Database …
How to Convert a Single-Instance Oracle Database to RAC
Single Instance–to-RAC Conversion A single-instance Oracle database can be converted using several methods, which …
How to Install and Configure Oracle RAC 12c
Installing the Oracle Database Software The Oracle Universal Installer (OUI) is used to install the Oracle Database 12c …
How to Create an Oracle Data Guard Broker Configuration
Data Guard Broker: Requirements To use the Data Guard broker, you must comply with the following requirements: Use the …
Beginners Guide to Oracle Data Guard Broker
The Oracle Data Guard broker is a distributed management framework. The broker automates and centralizes the creation, …
Creating a Logical Standby Database by Using Enterprise Manager
To create a logical standby database by using Enterprise Manager: 1. Click Add Standby Database on the Data Guard …
Oracle Data Guard: Creating a Logical Standby Database
Benefits of Implementing a Logical Standby Database A logical standby database provides benefits in disaster recovery, …
How to Enable RMAN Block Change Tracking for a Physical Standby Database
Enabling Block Change Tracking on a Physical Standby Database With the Oracle Active Data Guard option, you can enable …
How to Use Data Guard 12c Far Sync Feature
What is a Far Sync? A Data Guard Far Sync is a remote Data Guard destination that accepts redo from the primary database …
ACPI v/S APIC Kernel Boot Options
ACPI ACPI stands for Advanced Configuration and Power Interface. It is the system that describes hardware to the …
How to Create Physical Standby Database by Using Oracle Enterprise Manager Cloud Control
Prerequisites for Using Oracle Enterprise Manager Cloud Control 12c Oracle Enterprise Manager Cloud Control 12c can …
Beginners Guide to Oracle Data Guard
Oracle Data Guard is a central component of an integrated Oracle Database High Availability (HA) solution set that helps …
Beginners Guide to Oracle RAC Architecture
Oracle RAC: Overview A cluster comprises multiple interconnected computers or servers that appear as if they were one …
Beginners Guide to Oracle Clusterware Architecture
Cluster A cluster consists of a group of independent but interconnected computers whose combined resources can be …
Beginners Guide to Oracle Clusterware Architecture and Cluster Services
Oracle Clusterware provides a complete set of cluster services to support the shared disk, load balancing cluster …
How to Create the RMAN Recovery Catalog
What is the RMAN Catalog Schema, Repository and Database? The RMAN catalog schema is an Oracle Schema holding the RMAN …
How to Upgrade the RMAN Recovery Catalog
What is the RMAN Catalog Schema, Repository and Database? The RMAN catalog schema is an Oracle Schema holding the RMAN …
RMAN Recovery Catalog Interview Questions
What is the RMAN Catalog Schema, Repository and Database? The RMAN catalog schema is an Oracle Schema holding the RMAN …
How to Estimate the Size of Redo Logs
The best way to determine the optimal size of redo log files is to look into the alert.log file for messages about how …
How to Resize the Online Redo Logfiles in Oracle Database
Often times the online redo logs are sized too small causing database performance problems. The following is an example …
Understanding Linux Multipath Configuration File /Etc/Multipath.conf
DM-Multipath allows many of the features to be user-configurable using the configuration file /etc/multipath.conf. …
"/Dev/Sdxx: Read Failed After 0 of 4096 at 0: Input/Output Error" - On Running LVM Commands Like Pvscan
The Problem LVM commands show disk read failure and shows the below I/O errors: [root@server]# pvscan /dev/sdxx: read …
How to Configure Rsh and Rlogin on CentOS/RHEL 7
Basics The rsh and rlogin services enable to respectively execute a command and login from a remote host. It has been …
How to Configure Rsh CentOS/RHEL 6
Basics The rsh, rlogin, and rexec server should only be run on a system after carefully considering the security …
How to Disable Medium Ciphers in Open LDAP
Server The configuration file for openldap server is as below, /etc/openldap/slapd.conf Need to add the following line …
How to Check and Change the Clock Source in CentOS/RHEL 6,7 and 8
An overview on hardware clock and system timer circuits When it comes to talking about a system’s clock, the …
Kernel Boot Parameters "Hpet=disable" v/S "Nohpet"
Kernel boot parameter HPET (High Precision Event Timer) is used for specifying hardware timer/clock source. HPET is not …
Leap Seconds in Linux
What are leap seconds You can read more than you’ll ever want to know on the web, but I recommend the Unix Leap …
Error: 1040, Too Many Connections (MySQL)
Error 1040 occurs when the number of connected clients has reached the value of the max_connections server variable. …
Script to Collection NTP Information in CentOS/RHEL Server
This script collects information about the configuration and the status of a Linux NTP daemon and all system information …
All About RPM Utility
RPM stands for Redhat Package Manager. It is a utility that is used to install, uninstall, update, query, and verify …
Ansible Installation on Linux
Ansible is an open-source automation platform. It is simple to install. The Ansible software only needs to be installed …
How to Copy Files to Remote Server With Sudo Privileges
Today, I come across a situation where I have to push a file to the remote server’s directory which was owned by user …
How to Remove Duplicate Packages in CentOS/RHEL
Today, I come across a situation where, while patching an RHEL server yum update command got interrupted and started …
Not Able to Delete Files When the Number of Files Is Very Large
When we have to do operations on a huge number of files then find command comes to our rescue. There can be situations …
Automate Linux Patching Using Ansible
Ansible comes with a module named YUM with the help of which the activities of package installation, upgrade, and …
Automate Root Password Change Using Ansible Playbook
Updating/Changing the root user’s password is a routine task being performed by every Linux administrator in any …
Cronjob Interview Questions
1) How to execute a Linux cron job every second using Crontab? Answer: You cannot schedule a every-second cronjob. In …
How to Recover Default File & Directory Permissions
Today, I come across a situation where, an application guy hit chmod command in wrong way. He hit below command where …
How to Reload New Kernel Without Complete Reboot in CentOS/RHEL
We all know that it is possible to update the kernel with a server reboot but, a restart is needed in order to make use …
SELinux Interview Questions
1) What are Booleans? Answer: Booleans are SELinux policy rules which changes behaviour of selinux policies. Booleans …
Using TAR Command Practically in Linux
tar is a commonly used command to create archive files. TAR stands for Tape ARchive. It is important to note that tar is …
Ansible Playbook Task to Delete All Contents of a Directory
Today, I came across a situation where I had to write a task in an ansible playbook to delete the contents of …
Ansible Playbook to Migrate RHEL Servers From Satellite5 to Satellite6
Below Playbook can be used to migrate any RHEL6 or RHEL7 server from Satellite version 5 to Satellite version 6.
Easiest Way to Exclude NFS Mount Points in Find Command
Today, I was told to remove a domain group from the active directory. However, there were files/directories owned by …
Easiest Way to Increase Linux LVM by Expanding Virtual Disk
Today, I come across a situation where I had to increase the size of lvm partition without adding a new virtual disk.
How to Append a Text/Line to Root Owned Files With Sudo Access
Today, I came across a situation where I was writing a script for automation. In the script, I had to append a line to …
How to Check if Server Is BIOS/UEFI Booted in CentOS/RHEL
If you are planning to use a hard disk of size more than 2TB UEFI comes into the picture. Today, I came across a …
KVM: Common Issues and How to Troubleshoot Them
This post lists KVM known issues, how to troubleshoot and resolve them. Error: Log files There are various trace/log …
How Does Network Partitioning Affect MySQL Cluster?
Network partitioning is when there is a network outage that causes the cluster to be split into two survivable groups. …
What Are Nodegroups in MySQL Cluster
A node group is a set of data nodes that is in charge of several fragments of data in the MySQL Cluster.
Understanding Fractured Block and ORA-1578 Error
ORA-1578 error could be an indication of a Fractured Block. A Fractured Block means that the block is incomplete and …
How Does Vm.swappiness Value Affects System Performance
The kernel uses heuristics to guess which pages of memory are likely to be needed in the near future and tries to keep …
Failed to Synchronize Cache for Repo 'Repo_name', Ignoring This Repo.
The Problem While installing package or listing using dnf or yum commands getting below errors: # dnf repolist Oracle …
How to Use Truss, Pstack, and DTrace to Debug High CPU Type Problems on Solaris
This post describes ways to begin to diagnose why a process is using more CPU than normal. Why is this abnormal?
Oracle SQL Script to Report Table Fragmentation
Access Privileges: Requires user with SELECT privileges on DBA_TABLES, DBA_SEGMENTS, DBA_EXTENTS and ANALYZE privilege …
How to Use Strace in Linux to Debug Process Hung Issues
The strace utility is a debugging utility for Linux which is used to monitor the system calls used by a program and all …
How to Automatically Start STRACE or TRUSS With PL/SQL
Why to Start STRACE and TRUSS with PL/SQL There are times when a STRACE or TRUSS tracing utilities would help diagnose …
"Fork of '/Bin/Systemd-Detect-Virt' Failed: Cannot Allocate Memory" - CentOS/RHEL 7 Booting Issue
The Problem System fails to boot with below errors: [12.524044] systemd-udevd: fork of '/bin/uname -p' failed: …
"Kernel Panic - Not Syncing: Out of Memory and No Killable Processes..." CentOS/RHEL Booting Issue Due to Incorrect HugePages Setting
The Problem System boots into “kernel panic - not syncing: Out of memory and no killable processes…”. …
How to Install/Upgrade MySQL Packages on Ubuntu Using Dpkg Command
1. Download the MySQL packages for ubuntu. 2. Upload the zip file to the Ubuntu and unzip it. (unzip was not install by …
How to Setup the Oracle Java Plug-in on Ubuntu Linux
Ubuntu is a Certified System Configuration for Java SE 7. This article describes how you can setup the Oracle Java …
Kickstart Install Failure "Illegal IP Address String Passed to Inet_aton."
The Problem CentOS/RHEL 7.2 kickstart install fails with following error if the following option’s are used, …
Cannot Add Dependency Service.R to Multi-User.target, Ignoring: Invalid Argument
The Problem Multiple systemd services has been failing to initialize due to Cannot add dependency issues: Hostname …
How to Determine Which /Dev/Mapper/ Device Corresponds to /Dev/Dm-* Device in CentOS/RHEL
When native Linux device multipathing is used, an error may be reported that lists the composite multipath device. For …
How to Find Blocking InnoDB Connections in MySQL and Then Kill Those Connections
As of MySQL 5.5, you can use these 2 INFORMATION_SCHEMA views : INNODB_LOCK_WAITS INNODB_TRX Here is an example: session …
How to Remove DBFS Configuration on EXDATA Systems
This post discusses the Removal of DBFS configuration steps specific to EXADATA systems. This needs to be tested in your …
How to Create a TDE Auto_Login Wallet for a Database With Oracle Key Vault OKV TDE Direct Connection / Online Master Key
This post assumes the existence of an Oracle Key Vault server with an endpoint enrolled. The variables ORACLE_SID, …
How to Identify the Dom0 Version (Oracle VM Server Version) From a Virtual Machine
Question: How to identify the dom0 Version from a Virtual Machine? The DMI output in the dmesg commands tells about the …
How to Migrate Existing TDE Wallet to Oracle Key Vault for a 12c Oracle RAC Database
This post details the steps needed to be performed to migrate an existing TDE wallet for a RAC database to an OKV …
How to Migrate TDE Local Wallet to Oracle Key Vault (OKV) Server
This post provides steps to migrate TDE local wallet to Oracle Key Vault Server. Assuming that, TDE local wallet is …
./Sqlplus: Error on Libnnz11.so: Cannot Restore Segment Prot After Reloc
The Problem Immediately after a successful RDBMS installation (perhaps even including a sample DB instance creation), …
Apache Fails to Start With "Libonssys.so: Cannot Open Shared Object File: No Such File or Directory" After Weblogic Plugin Is Configured
The Problem Apache is installed on Oracle Linux through “yum install httpd”. After the install the Apache …
How to Set Hostname During Kickstart Installation (CentOS/RHEL 5,6,7)
For CentOS/RHEL 5 and 6 Here, you can specify the hostname as a boot parameter in Anaconda, then set the hostname from …
Installing UEFI Linux With Kickstart
Question: How to perform a UEFI Linux installation through kickstart for non DHCP/PXE? The steps outlined below explians …
Error "Can't Open Display: Localhost:x.y" When Running Xclock on Xming
The Problem Unable to do Display Setting for Xming. You get the error below while trying to run Xclock on server for …
How to Install Java Development Kit 6 on CentOS/RHEL
This post shows how to install and configure Java Development Kit 6 on CentOS/RHEL. Download Java Development Kit 6 You …
How to Check Connections Waiting for Lock Other Than an InnoDB Row Lock in MySQL
Question: How to Check Whether Any Queries Are Waiting for a Lock Other Than an InnoDB Row Lock? You can use the …
How to Check Number of Innodb Deadlocks That Have Occurred
Question: How to Monitor Number of InnoDB Deadlocks? To log all deadlock information to the mysql error log, you can …
How to Prompt for Hostname During Kickstart Installation (CentOS/RHEL 6 and 7)
This post describes the steps to prompt for server hostname during kickstart install. The hostname parameter can be …
MySQL - 'FLUSH TABLES WITH READ LOCK' Is Pending for a Long Time
The Problem After issuing FLUSH TABLES WITH READ LOCK, we can see it is pended for a long time with one of the following …
What Is the Difference Between HISTSIZE and HISTFILESIZE
In bash, by default, the history commands are recorded in ~/.bash\_history. You can specify a different file other than …
Java.lang.OutOfMemoryError: Requested 32756 Bytes for ChunkPool::allocate. Out of Swap Space?
The Problem The Java Virtual Machine (JVM) crashed. The fatal error log file, hs_err_pid[pid].log, shows the error …
How to Change the Home Directory of the Oracle Secure Backup (OSB) to Its Default Location (/Usr/Local/Oracle/Backup)
Question: How to change the home directory of the Oracle Secure Backup (OSB) to its default location, which is …
Unable SSH to System After Installing Updates (CentOS/RHEL 7)
The Problem Unable to connect to one of the systems after installing many software updates from the standard Oracle …
How to Set the Password Policy Such That User Cannot Use Any of the Previous 3 Passwords in CentOS/RHEL 6
Question: How to change the password policy on a system so that a user cannot choose any of the last 3 passwords …
Oracle Key Vault Interview Questions
How to check the existence of the persistence master key cache? The documentation says: “The persistent master key …
How to Install ASMLib on OEL 8
What is ASMLib? ASMLib is free, optional software for the Automatic Storage Management (ASM) feature of Oracle Database …
Enable OS Management Service (OSMS Agent) for a Oracle Linux 8 Instance (OCI Linux)
By default, the OS Management Service Agent plugin is enabled on Oracle Linux 6 and 7 instances. For Oracle Linux 8 …
How to Configure VNC Server in CentOS/RHEL 8
This post explains the steps to easily setup VNC server in CentOS/RHEL 8. Should be able to access VNC session after …
How to Track Shell Activities of Users in CentOS/RHEL
This post helps to save the command history of selected users to a centralized location for monitoring purposes. 1. …
How to Configure Network Interface Teaming in CentOS/RHEL 7 and 8
Network interface teaming was introduced from CentOS/RHEL 7 as a more extensible and scalable alternative to network …
How to Configure Passwordless SSH in Linux
SSH is a protocol to transfer data securely between different machines. The SSH protocol uses public-key cryptography to …
Setup Flask With Apache and Wsgi
Why use Apache Using Apache to serve your Flask App is, in my opinion, the easiest way to move out of development and …
What Is Privilege Analysis in Oracle Database
What is privilege analysis? - Privilege Analysis captures the privileges used by database users, including database …
How to Increase Dmesg Log Size to Capture More Verbose Booting Logs in CentOS/RHEL 7
Question: How do we capture debugging information from systemd during early boot issues? To avoid losing boot messages, …
How to Convert a General Purpose ACFS Filesystem to CRS Managed on Release 11.2./12.1
It is not uncommon for customers to configure an ACFS filesystem as an ACFS mount registry-based general-purpose …
How to Change Engine Database Password for OLVM Engine
This post illustrates steps to change the engine database password for the OLVM engine. 1. Before modification, you can …
Oracle Linux Virtualization Manager(OLVM) Engine PostgreSQL Database Queries Cheat Sheet
This post will explain some practical psql commands and describe how to run the PostgreSQL queries from the command line …
How to Configure Firewalld in CentOS/RHEL 8 Using "Web Console" and "Firewall-Cmd"
Firewall Architecture Concepts The Linux kernel includes netfilter, a framework for network traffic operations such as …
Troubleshooting Booting Issues in CentOS/RHEL 7 and 8
The operating systems break and crash. We as sysadmin are always looking for the root cause analysis so as to avoid such …
How to Mount NFS Shares Using Automounter in CentOS/RHEL
Mounting NFS Shares with the Automounter The automounter is a service (autofs) that automatically mounts NFS shares …
How to Reset or Recover Root Password in CentOS/RHEL 8
Resetting the root password from the Boot Loader One task that every system administrator should be able to accomplish …
Understanding CentOS/RHEL 8 Boot Process
Step by Step Linux Boot Process (CentOS/RHEL 8) Modern computer systems are complex combinations of hardware and …
Beginners Guide to Stratis Local Storage Management in CentOS/RHEL 8
Describing the Stratis Architecture The current local storage solution in CentOS/RHEL includes many stable and mature …
How to Compress and Deduplicate Storage With VDO in CentOS/RHEL 8
Describing Virtual Data Optimizer CentOS/RHEL 8 includes the Virtual Data Optimizer (VDO) driver, which optimizes the …
How to Extend a Logical Volume in LVM - For XFS, Ext4 and Swap Filesystem
Extending a logical volume and XFS file system One benefit of logical volumes is the ability to increase their size …
How to Extend and Reduce a Volume Group in LVM
Extending and Reducing a Volume Group You can add more disk space to a volume group by adding additional physical …
How to Mount and Umount NFS Share in Linux
NFS, the Network File System, is an internet standard protocol used by Linux, UNIX, and similar operating systems as …
How to Create Logical Volumes (LV) in LVM
Logical Volume Management (LVM) Concepts Logical volumes and logical volume management make it easier to manage disk …
Beginners Guide to Scheduling Periodic Tasks in Linux Using Cron
Performing Periodic Tasks Often, people find that they are (or ought to be) performing tasks on a regular basis. In …
Job Control in Linux Using Bg, Fg and Jobs Commands
Running Commands in the Foreground When running a command from the bash shell prompt, unless you specify otherwise, the …
How to Send Signals to Processes With Kill in Linux
Signals Linux (and Unix) uses signals to notify processes of abnormal events, and as a primitive mechanism of …
"Alias" Command in Linux
The alias command is one of many commands referred to as Bash Built-In commands, meaning it is inherent to the bash …
16 Quotacheck Command Examples in Linux
quotacheck command audits and corrects quota information by building a table of current disk usage and comparing it to …
Beginners Guide to AWS IAM
In this post, we will discuss the AWS IAM feature. We will cover some of the basic features that IAM provides and dene …
Beginners Guide to LUKS Disk Encryption in Linux
Let us talk about something on security hardening in Linux. the first topic that comes to mind is Disk encryption. The …
Create and Deploy POD Definitions in Kubernetes
In this guide, we will be working on How you can Create and Deploy Pod Definitions in a Kubernetes cluster and run …
How to Change a Process’s Priority Using Nice and Renice Commands in Linux
Process Priorities When scheduling processes, the kernel effectively gives every process a handful of counters. Every …
How to Configure a PXE Server in CentOS/RHEL 7
The Preboot Execution Environment (PXE) is an industry-standard client/server interface that allows networked computers …
How to Configure Apache Virtual Host in CentOS/RHEL 7
Apache HTTPD is one of the most used web servers on the internet. A web server is a daemon that speaks the http(s) …
How to Configure Password Less SSH Using Ssh-Keygen in Linux
SSH (Secure SHELL) is an open-source and most trusted network protocol that is used to login to remote servers for the …
How to Configure PXE Server to Install SuSE Linux Enterprise Server 11
In this post, we will discuss how do we configure the PXE server to install SuSE Linux Enterprise server OS into …
How to Configure YUM Repository Server Using Apache Webserver in CentOS/RHEL 7
Here is a quick reference guide on configuring an apache webserver based YUM repository server in CentOS/RHEL 7. …
How to Disable and Clear Linux Command Line History
When you type commands in the bash shell, the shell by default is recording every command that you input via the …
How to Enable IP Forwarding in Linux
IP forwarding is a process of forwarding IP packets received on one network interface to another network interface. This …
How to Install Ansible on Ubuntu 18.04
In this tutorial, we will show you how to install ansible and ansible playbook on Ubuntu 18.04. This tutorial will show …
How to Scan a New Disk in CentOS/RHEL Online (Without Reboot)
This post discusses - how to scan a new disk without rebooting the system. Sometimes the new disks are not scanned …
How to Troubleshoot Sendmail in Solaris
In this post, we are going to discuss the Sendmail Configuration and Troubleshoot method, as this Sendmail service very …
Iptables Command Line Reference (Cheat Sheet)
Please note that the iptables rules are stored in the /etc/sysconfig/iptables file. If you view this file, you’ll see …
Linux "Shutdown" Command Examples
The shutdown Command “shutdown” is a system administration command which terminates all processing. when …
Linux Poweroff Command
The Linux poweroff command closes out the filesystem, shuts down the system, and poweroff it. Because this command …
Linux Sort Command Examples
The Linux Sort can be used to sort the content of a text file or output from other commands, By default, the sort …
Linux Whoami Command
whoami is a very simple Linux command and can be used to find out the name of user who is currently logged in the …
Managing System Clock Using Chrony in CentOS/RHEL 7
The chrony package provides a chronyd service daemon and chronyc utility that enable mobile systems and virtual machines …
Sdiff Command in Linux With Examples
The sdiff command produces a side-by-side comparison of file1 with file2. Output is shown in the format: text text …
Solaris 11 - Beginners Guide to Network Administration / Link Aggregation / IPMP
Last post we have gone through some basics of Network administration. In this post, we will be targeting some Advance …
Solaris Interview Questions - User Management
The intent of this post is to help the person who is going to attend the basic level of the Solaris interview.
The 3 Best System Monitoring Tools for Ubuntu
As the number of devices, servers, and services in your business or organization increases, it is time to monitor …
To Add and Configure New Volumes on a Current Volume Group in LVM
Question: How to add a new volume to an existing LVM volume group. Note: This post assumes that there is an existing …
Uniq Command in Linux
The uniq command can be used to remove the duplicate lines from a text file in Linux or Unix. The duplicate lines should …
What Are Types of Processes and Process States in Linux
How a Process Dies When a process dies, it either dies normally by electing to exit, or abnormally as the result of …
What Is a Process in Linux
Processes are an instance of an executing program. In other operating systems, programs are often large, elaborate, …
Beginners Guide to Adding Partitions and Creating Filesystems in Linux
Partitioning a Disk Disk partitioning allows system administrators to divide a hard drive into multiple logical storage …
Cut Command in Linux With Examples
Extracting Text with cut The cut command extracts columns of text from a text file or stream. Imagine taking a sheet of …
How to Create and Manage Swap Space in Linux
Introducing swap space concepts A swap space is an area of a disk under the control of the Linux kernel memory …
Linux Aspell Command for Spell Checking
In Linux, the aspell utility is the primary utility for checking the spelling of text files. In this post, we learn how …
Paste Command in Linux With Examples
The paste command is used to combine multiple files into a single output. Recall the fictional piece of paper which …
Uniq Command in Linux With Examples
The uniq program is used to identify, count, or remove duplicate records in sorted data. If given command-line …
Cat, Head and Tail Command in Linux With Examples
Linux cat command We have been using the cat command to simply display the contents of files. Usually, the cat command …
Linux Commands Grep, Fgrep and Egrep With Examples
Searching Text File Contents using grep In an earlier post, we saw how the wc program can be used to count the …
Sort Command in Linux With Examples
Sorting is the process of arranging records into a specified sequence. Examples of sorting would be arranging a list of …
Wc Command in Linux With Examples
Counting Made Easy Have you ever tried to answer a “25 words or less” quiz? Did you ever have to write a 1500-word …
Beginners Guide to Troubleshooting Common SELinux Issues
It is important to understand what actions you must take when SELinux prevents access to files on a server that you know …
Beginners Guide to SELinux Modes in Linux
How SELinux Protects Resources SELinux provides a critical security purpose in Linux, permitting or denying access to …
How to Manually Re-Enable Failed Paths Reported by Multipath in CentOS/RHEL
The Problem When running the multipath command it could be seen devices reporting failed paths, like “sdb” …
Managing SELinux File Contexts
Initial SELinux Contexts On systems running SELinux, all processes and files are labeled. The label represents the …
Managing SELinux Policy With Booleans (Setsebool)
SELinux Booleans SELinux booleans are switches that change the behavior of the SELinux policy. SELinux booleans are …
Beginners Guide to Access Control Lists (ACLs) in Linux
Access Control List Concepts Standard Linux file permissions are satisfactory when files are used by only a single …
Beginners Guide to Scheduling Jobs in Linux Using Cron and Systemd Timer
Jobs scheduled to run repeatedly are called recurring jobs. Most Linux systems ship with the crond daemon, provided by …
How to Schedule Jobs to Run Using "At" Command in Linux
Why we need at instead of cron to schedule jobs Sometimes you might need to run a command, or set of commands, at a set …
How to Use Nice and Renice Commands in Linux to Prioritize or De-Prioritize Specific Processes
Linux Process Scheduling and Multi-Tasking Modern computer systems range from low-end systems that have single CPUs that …
Understanding Systemd-Tmpfiles to Manage Temporary Files and Directories in CentOS/RHEL
Managing Temporary Files A modern system requires a large number of temporary files and directories. Some applications …
Beginners Guide to Writing Bash Shell Scripts
Creating and Executing Bash Shell Scripts Many simple, common system administration tasks are accomplished using …
How to Create Conditional Structures in Shell Scripts Using if Statements
Conditional Structures Simple shell scripts represent a collection of commands that are executed from beginning to end. …
How to Use Exit Codes and Test Inputs in Shell Scripts
Using exit codes within a script After a script has processed all of its contents, it exits to the process that called …
How to Use for Loop in Bash Script
Using for loop to iterate commands System administrators often encounter repetitive tasks in their day-to-day …
Examples of Find and Locate Command to Search Files on Linux
Searching for files A system administrator needs tools to search for files matching certain criteria on the file system. …
How to Provision Multiple User Accounts on Multiple Servers Using Ansible
The User Module The Ansible user module lets you manage user accounts on a remote host. You can manage a number of …
How to Mount and Umount the FileSystems in Linux
Mounting File Systems Manually A file system residing on a removable storage device needs to be mounted in order to …
Oracle WebLogic Server - How to Change Password of Java Keystores
Please follow the steps outlined below in order to change the password of Java keystores in their production …
How to Configure YUM Repositories in CentOS/RHEL 7 and 8
Enabling RedHat Software Repositories Registering a system to the subscription management service automatically …
How to Install and Update Software Packages Using the Yum Command
Managing Software Packages with YUM The low-level rpm command can be used to install packages, but it is not designed to …
Rpm Command Examples in Linux
Software Packages and rpm The RPM Package Manager, originally developed by Red Hat, provides a standard way to package …
Understanding File Systems and Mount Points in Linux
Storage Management Concepts Files on a Linux server are accessed through the file-system hierarchy, a single inverted …
How to Archive and Extract Files/Directories Using "Tar" in Linux
The tar Command Archiving and compressing files are useful when creating backups and transferring data across a network. …
How to Configure the Hostname and Name Resolution in CentOS/RHEL 7 and 8
Changing the system hostname The hostname command displays or temporarily modifies the system’s fully qualified host …
How to Manage Network Settings and Devices Using the Nmcli Command
NetworkManager Basics NetworkManager is a daemon that monitors and manages network settings. In addition to the daemon, …
How to Modify Network Configuration by Editing Configuration Files in CentOS/RHEL 7 and 8
DESCRIBING CONNECTION CONFIGURATION FILES By default, changes made with nmcli con mod name are automatically saved to …
How to Transfer Files in Linux Using Scp and Sftp
Transfering files using Secure Copy (scp) OpenSSH is useful for securely running shell commands on remote systems. The …
How to Use Rsync to Securely Copy Files From One System to Another
Synchronize files and directories with rsync The rsync command is another way to securely copy files from one system to …
How to View and Test Current Network Configuration in CentOS/RHEL
Starting from CentOS/RHEL 7, various new features have been introduced in the network stack as well. This post will …
Fundamental Concepts of Network Addressing and Routing for a Linux Server
TCP/IP Network Model The TCP/IP network model is a simplified, four-layered set of abstractions that describes how …
How to Configure and Monitoring Chronyd in CentOS/RHEL 7 and 8
The chronyd service keeps the usually-inaccurate local hardware clock (RTC) on track by synchronizing it to the …
How to Configure the System Journal to Preserve the Record of Events When a Server Is Rebooted (CentOS/RHEL)
Storing the system journal permanently By default, the system journals are kept in the /run/log/journal directory, which …
How to Synchronize Time Using NTP and Set Timezone in CentOS/RHEL 7 and 8
Setting local clocks and time zones Correct synchronized system time is critical for log file analysis across multiple …
How to Use Journalctl to View Log Messages in Journal for System Troubleshooting
Finding Events The systemd-journald service stores logging data in a structured, indexed binary file called the journal. …
Beginners Guide to CentOS/RHEL Logging (Systemd-Journald and Rsyslog) Architecture
System Logging Processes and the operating system kernel record a log of events that happen. These logs are used to …
How to Restrict Direct Logins as Root and Disable Password-Based Authentication for SSH
Configure the OpenSSH Server OpenSSH service is provided by a daemon called sshd. Its main configuration file is …
Overview of Syslog Priorities, Rsyslog Rules, Log Rotation and Basic Troubleshooting Using Syslog
Logging events to the system Many programs use the syslog protocol to log events to the system. Each log message is …
Beginners Guide to Configuring Secure Command-Line Service on Remote Systems, Using OpenSSH
What is OpenSSH OpenSSH implements the Secure Shell or SSH protocol in the Red Hat Enterprise Linux systems. The SSH …
Beginners Guide to Managing Services Using Systemd
Introduction to systemd The systemd daemon manages startup for Linux, including service startup and service management …
How to Configure Ssh Key-Based Authentication to Login to Remote Host
SSH Key-based Authentication You can configure an SSH server to allow you to authenticate without a password by using …
How to Control (Start/Stop/Mask/Unmask) Services Using Systemd
Starting and Stopping Services Services need to be stopped or started manually for a number of reasons: perhaps the …
Beginners Guide to Linux File System Permissions
Linux Filesystem Permissions File permissions control access to files. The Linux file permissions system is simple but …
Beginners Guide to Managing Processes Running on a Linux System
Definition of a Process A process is a running instance of a launched, executable program. A process consists of: An …
How to Change the Permissions and Ownership of Files in Linux
The command used to change permissions from the command line is chmod, which means “change mode” …
How to Control Processes in Linux Using Bg, Fg and Jobs Commands
Describing Jobs and Sessions Job control is a feature of the shell which allows a single shell instance to run and …
How to Control the Default Permissions of New Files Created by Users Using "Umask"
Default File Permissions When you create a new file or directory, it is assigned initial permissions. There are two …
How to Create, Modify, and Delete Local Group Accounts in Linux
A group must exist before a user can be added to that group. Several command-line tools are used to manage local group …
How to Create, Modify, and Delete Local User Accounts in Linux
A number of command-line tools can be used to manage local user accounts. Creating Users from the Command Line The …
How to Kill Processes in Linux Using - Kill, Pkill, Killall
Process Control Using Signals A signal is a software interrupt delivered to a process. Signals report events to an …
How to Set a Password Management Policy for Users, and Manually Lock and Unlock User Accounts in CentOS/RHEL
shadow passwords and password policy At one time, encrypted passwords were stored in the world-readable /etc/passwd file. …
How to Switch User Account and Configure Sudo in Linux
The SuperUser Most operating systems have some sort of superuser, a user that has all power over the system. In Linux, …
Interpreting Displayed Load Average Values in "Uptime" Command Output
Describing Load Average Load average is a measurement provided by the Linux kernel that is a simple way to represent the …
Understanding 'Top' Command Output Fields in Linux
Real-Time Process Monitoring The top program is a dynamic view of the system’s processes, displaying a summary …
Understanding Linux Special Permissions - Sticky Bit, SUID, SGID
Special Permissions Special permissions constitute a fourth permission type in addition to the basic user, group, and …
"There Are # Physical Volumes Missing" - Error in Pvscan Even When the PVs Are Present
The Problem The output of pvscan command shows ‘There are # physical volumes missing’, but these physical …
Beginners Guide to Editing Files in Linux With VIM
A key design principle of Linux is that information and configuration settings are commonly stored in text-based files. …
Beginners Guide to User and Group Administration on a Linux System
In this post and in future posts in the series, we will learn how to create, manage, and delete local users and groups …
Beginners Guide to Using Shell Variables in Linux
Using Shell Variables The Bash shell allows you to set shell variables that you can use to help run commands or to …
How to Create Hard Links and Symbolic (Or "Soft") Links in Linux
It is possible to create multiple names that point to the same file. There are two ways to do this: by creating a hard …
How to Create, Copy, Move, and Remove Files and Directories in Linux
Command line file management To manage files, you need to be able to create, remove, copy, and move them. You also need …
How to Process Command Output Through Multiple Command-Line Programs With Pipes in Linux
Constructiong Pipelines A pipeline is a sequence of one or more commands separated by the pipe character (|). A pipe …
How to Run Commands Affecting Many Files by Using Pattern Matching Features of the Bash Shell
Command-Line Expansions The Bash shell has multiple ways of expanding a command line including pattern matching, home …
How to Save Output or Errors to a File With Linux Shell Redirection
Standard Input, Standard Output and Standard Error A running program, or process, needs to read input from somewhere and …
ORA-28007: The Password Cannot Be Reused
The Problem You attempt to alter a user’s password to a previously used one and get the following error when …
Understanding GNU Info Command in Linux
Introducing GNU info Man pages have a format useful as a command reference, but less useful as general documentation. …
Understanding Linux Man Pages
Introducing the Man Command One source of documentation that is generally available on the local system are system …
How Linux Organizes Files and the Purposes of Various Directories in the File-System Hierarchy
The file system hierarchy All files on a Linux system are stored on file systems, which are organized into a single …
How to Login and Logout of a Remote Linux Server Using Ssh
Logging in Linux users and administrators often need to get shell access to a remote system by connecting to it over the …
How to Use Ethtool to Change Speed, Duplex, and Auto-Negotiation Settings in Linux
This post describes how to change network device settings, such as speed, duplex, and auto-negotiation in Linux with …
Why Should You Learn Linux
Linux is a critical technology for IT professionals to understand. Linux is in widespread use, and if you use the …
How to Clear Stuck NFS Locks on NetApp Filer(s)
Question: We are using NFS for datafile storage, without Real Application Clusters (RAC), and the mount point with the …
How to Install KDE Desktop Environment in CentOS/RHEL 6
This post describes how to install the KDE Desktop environment in a CentOS/RHEL 6.x system where it is not yet …
How to Set Tcp/Ip Parameters Persistently on Solaris 11
Question: How to set tcp/ip parameters to Become permanent after reboot on Solaris 11? Below are a few examples of how …
Oracle Database - Reading an Export File Using Import Without Physically Importing Data
The purpose of this post is to briefly describe how to list objects in an export file without physically importing the …
CentOS/RHEL 7 - Gdm Getting Crashed and Unable to Login via GUI
The Problem User cannot login to the system via GUI On CentOS/RHEL 7.x. The gdm utility segfault with below error after …
"/Etc/Init.d/Oracleasm Is Deprecated in Favor of Userspace Tool /Usr/Sbin/Oracleasm" - Error While Restarting Oracleasm Service
The Problem We had Upgraded oracleasm tools and system to latest. Restarting the oracleasm service triggers below …
How to Replace a Failed Disk Mirrored With the Raidctl Command in Solaris
This post describes the process of replacing a failed disk with the raidctl command in the mirroring configuration on …
How to Start and Shutdown CRS, OHAS, ASM, RDBMS & ACFS Services on Oracle RAC Cluster 11.2 & 12.1
The post provides in detail the steps to shutdown/startup The CRS, OHAS, ASM & RDBMS Services on a RAC Cluster 11.
MySQL Interview Questions - MySQL Plugin Architecture
This post answers the most common questions of the MySQL Plugin architecture. Answers cover areas such as installation, …
Oracle Database - How to Unset DB_FILE_MULTIBLOCK_READ_COUNT to Default Value
Question: DB_FILE_MULTIBLOCK_READ_COUNT is set to 16 in the spfile. How to unset the parameter as it keeps reverting …
Understanding the Oracle Resource Profile Parameters PASSWORD_REUSE_MAX and PASSWORD_REUSE_TIME
This post talks about the change of behavior for the PASSWORD_REUSE_MAX and PASSWORD_REUSE_TIME resource profile …
How to Check Oracle Database Accounts Without Profiles That Have a Default Password
This post explains about how to check database accounts without profiles have default password. When a profile is …
How to Move Tables Between Tablespaces Using Traditional Oracle Export/Import (EXP/IMP)
This post discusses three ways you can move tables from one tablespace to another tablespace using traditional …
Understanding ACCOUNT_STATUS Column in DBA_USERS View
This post explains the meaning of the ACCOUNT_STATUS column of the DBA_USERS view. The DBA_USERS.ACCOUNT_STATUS can have …
How to Trace the Password Change History of Oracle Database Accounts
Question: How to Monitor Password Change History? Oracle only tracks the date that the password will expire based on …
CentOS/RHEL 7 : How to Recover Missing Grub.cfg File in Rescue Mode Using ISO
The Problem A system is not able to boot and is stuck at the GRUB prompt. The Solution The system can fail to boot if …
Understanding Oracle 18c New Feature - Schema Only Account
About Schema Only Accounts Schema is a collection of objects, while db user is an account to connect to the instance.
"Failed to Join Domain" - When Performing Realm Join on CentOS/RHEL 7
The Problem The “realm join” command is failing with the following error even if user is member of …
"Started Service Enabling Compressing RAM With ZRam" - CentOS/RHEL 7 Installation Hung
The Problem When installing CentOS/RHEL 7 on a hardware box with huge amount of ram installed, the installation gets …
"Writing Disk Header: Failed" - Error While Running "Oracleasm Renamedisk"
The Problem Unable to rename or delete the ASM disk. This disk is on multipath introduced to 2 node cluster. The disk is …
CentOS/RHEL 7 - Server Does Not Boot After Modifying the Default Kernel Entry in GRUB
The problem We have changed the default kernel entry to boot from in GRUB using the “grub2-set-default” …
How to Configure Yum-Cron to Send Email Notifications
This post outlines steps to configure yum-cron services and send an email notification. 1. Install the yum-cron package: …
How to Use MySQL Enterprise Backup (MEB) for Point-in-Time Recoveries (PITR)
If you want to be able to do a point-in-time recovery, you need to start your preparation already when creating the …
Too Many Kdmflush Processes Observed Causing ORA-27300, ORA-27301, ORA-27302 Errors
The Problem On CentOS/RHEL 6.x there are too many kdmflush processes owned by the root user which was notified after …
How to Control the Journal Size for Systemd in CentOS/RHEL 7 and 8
This post discusses how to control the journal size for systemd. The size limitations are governed by options in …
How to Disable NUMA (Non-Uniform Memory Architecture) on CentOS/RHEL 6
1. To disable NUMA, add numa=off to the kernel line in /boot/grub/grub.conf, for example: # vi /boot/grub/grub.conf …
How to Unmask a Masked Service in CentOS/RHEL 7 and 8
Problem systemd-tmpfile-clean.timer will not start, ignoring, unit is masked. # systemctl start …
Oracle Linux - Public Yum Repository v/S ULN
This post is to explain the difference between ULN (https://linux.oracle.com) and the Public Yum Repository …
Troubleshooting - Custom Systemd Service That Stops Immediately After Starting (CentOS/RHEL)
The Problem Service started with custom systemd script stops straight after starting. For example: # cat …
Troubleshooting Docker Stuck in Restarting Mode
Problem Container keeps stuck at restarting status as follows: # docker ps -a CONTAINER ID IMAGE COMMAND CREATED STATUS …
MySQL Server - Find Password Expire Date for Any User
Question: How to get the exact number of days left for the password to expire when the password expiry policy is …
Oracle Database Troubleshoot - Difference Between Freespace, Size of Tablespace and Usedspace
The Problem The free space as shown by the dba_free_space seems incorrect. The total space used by all the segments in …
How to Configure Docker HTTP Proxy to Retrieve Images in CentOS/RHEL 7 and 8
There are different locations where proxy configuration can be changed. In latest Docker distribution, it uses systemd …
Troubleshooting CGROUP I/O Throttling in CentOS/RHEL 7
The Problem The system is configured to use user slice cgroups to throttle the bandwidth on its Oracle ASM DATA and RECO …
Using SSL Connections With MySQL
To be able to use SSL for connecting to a MySQL server, the server will need to be reconfigured, and how clients access …
'Multipathd: Asm!.Asm_ctl_spec: Failed to Store Path Info' - Error in /Var/Log/Mesage
The Problem The following message will be seen in /var/log/messages when CRS stack is stopped/started. When stopping the …
"Multipathd: SdXX: Failed to Get Path Uid" - Native Multipath Layer Does Not Discover Physical Path Devices for LUN on CentOS/RHEL
The Problem The native multipath subsystem will group several physical paths into a single logical block device. Using …
Beginners Guide to MySQL Performance Tuning
The performance of MySQL is affected by the performance characteristics of the host. Various factors can affect the …
CentOS/RHEL 7 - Stale File Handle on Snapshot NFS Directories
The Problem A NetApp system is providing NFS shares which are accessed from several environments, including CentOS/RHEL …
How to Configure a Static IP Address on CentOS/RHEL 7
This post explains how a static IP address can be set on CentOS/RHEL 7. We can configure the static ip address in …
How to Discover Unhealthy Non-Global Zones and Fix Them in Solaris
Discovering unhealthy non-global zone states The Solaris Zone may be in different unhealthy situations, this post covers …
"Failed to Get Path Uid" - Multipathd Error Message With Non-Multipathed Devices
The Problem At the time starting multipathd, error messages like below are logged onto /var/log/messages with …
Interview Questions - Passwords and Password Policy in MySQL Server
Password Update and Reuse Policy Is there any feature for keeping track of user password history? MySQL 8.0 is able to …
Connect /as Sysdba Is Failing With Error ORA-12545
The Problem When trying to connect to a database as sysdba, ORA-12545 is occured and connection is failed. For Example:
How to Unset DB_FILE_MULTIBLOCK_READ_COUNT to Default Value in Oracle Database
Question: DB_FILE_MULTIBLOCK_READ_COUNT is set to 16 in the spfile. How to unset the parameter as it keeps reverting …
How to View and Set Dynamic and Static Oracle Database Parameters
There are two kinds of initialization parameters: Dynamic initialization parameters can be changed for the current …
How to Add, Remove, Replace or Move an Oracle Cluster Repository (OCR) and/or Voting Disk in Oracle Clusterware
The goal of this post is to provide steps to add, remove, replace or move an Oracle Cluster Repository (OCR) and/or …
How to Restore ASM Based OCR After Complete Loss of the CRS Diskgroup on Linux
It is not possible to directly restore a manual or automatic OCR backup if the OCR is located in an ASM disk group.
SQL Script to Report on Space in Tablespaces in Oracle Database
The script provided below will report On Space Usage in Tablespaces. Access Privileges required: SELECT on …
Beginners Guide to MySQL Replication
MySQL Replication Replication in MySQL copies changes from one server―the master―to one or more slaves. The master …
Beginners Guide to MySQL Backup and Recovery
If you are into systems, you would’ve heard about backups. I think in all fields backup is one thing which is of …
How to Create and Execute Triggers in MySQL
Triggers are named database objects that activate when you modify table data. They can: Examine data before it is …
How to Create, Alter, and Drop Events in MySQL
MySQL Events are tasks that run according to a schedule. They can be referred to as “scheduled events.” When you create …
Beginners Guide to Exporting and Importing Data in MySQL
Exporting and Importing Data The two most common ways to accomplish export and import operations are: Using SELECT …
How to Create and Execute Stored Routines in MySQL
Stored Routines A stored routine is a named set of SQL statements that are stored on the server. Clients do not need to …
How to Use SSL for Secure MySQL Server Connections
MySQL enables encryption on a per-connection basis. Depending on the requirements of individual applications, you can …
Beginners Guide to MySQL Partitioning
Partitioning A partition is the division of a database, or its constituting elements, into distinct independent parts. …
Understanding InnoDB Locking in MySQL Database
Locking InnoDB locking does not need to set locks to achieve consistent reads. It uses row-level locking for DML …
Beginners Guide to Transactions and Locking in MySQL
What is a MySQL Transaction A transaction is a way for you to execute one or more SQL statements as a single unit of …
How to Allow User Creation With Simple Password in MySQL
Question: How to allow user creation with simple password without any character limit or enforcement of special …
MySQL: How to Determine the Strength (Strong or Weak) of Current User Passwords
Question: How to Determine the Strength of Existing Passwords in Order to Identify Users with Weak Passwords? Find …
Beginners Guide to MySQL Tools
MySQL Tools Oracle Corporation provides tools for administering and otherwise working with the MySQL Server. 1. MySQL …
Understanding MySQL Command-Line Client Programs
The post describe the available clients for administrative tasks. Command-Line client programs available for MySQL are …
Beginners Guide to Oracle Database Initialization Parameters
About Initialization Parameters Managing an Oracle instance includes configuring parameters that affect the basic …
How to Configure MySQL Enterprise Auditing
Configuring Enterprise Audit Enterprize auditing can be implemented using the audit_log server plugin. It is available …
WARNING: Exec(): 0509-036 Cannot Load Program /App/12.2.0.1/Grid/Bin/Kfod.bin Durin Grid 12.2 Install on AIX
The Problem During 12.2.0.1 GI install on AIX 7.1, at OUI screen “create ASM disks”, asm disks are not …
What Are the Different Log Files Available in MySQL
Log Files MySQL has different log files to record server activity. Log files can consume a large amount of disk space.
Configure Operational Characteristics of the MySQL Server by Using the SQL Modes
SQL Modes The SQL mode consists of optional values that control some aspect of query processing. When you set the SQL …
What Are MySQL Server Status Variables
Server System Variables The MySQL server maintains many server system variables that indicate how it is configured. Each …
How to Avoid Passing MySQL User Password to Shell Script
In this post, we will learn how to avoid passing the password for the shell script manually. You can either:
How to Encrypt MySQL Password Using Mysql_config_editor
Obscuring Authentication Options Specifying a password on the command line in the form ‘mysql -u root -p …
How to Set Up MySQL Server Configuration Files
MySQL Configuration Options You can specify startup options on the command line when you invoke the server (or client), …
How to Start/Stop MySQL Server on Linux and Windows
Starting the MySQL Server on Linux The server can be started from a command line: # service mysql start Starting the …
What Are Linux/Windows MySQL Server Installation Directories
Linux MySQL Server Installation Directories When the RPM files are unpacked, many files are automatically extracted and …
Beginners Guide to MySQL Architecture
MySQL’s architecture is very different from that of other database servers and makes it useful for a wide range of …
What Are the Types of MySQL Server Software Distribution
MySQL Server Distributions MySQL is available for several operating systems, including Linux, Windows, Mac OS X, and …
"ORA-28365: Wallet Is Not Open" - While Running "RMAN DUPLICATE"
The Problem RMAN DUPLICATE fails with: ORA-00283: recovery session canceled due to errors ORA-28365: wallet is not open …
ORA-00257: Archiver Is Stuck. CONNECT INTERNAL Only, Until Freed
The Problem Your database is in archive log mode and archiving works fine until suddenly connecting via SQLPLUS …
Assigning Positional Parameter Values Using the Set Statement in Shell Scripts
Although you cannot use any positional parameter name on the left side of an assignment statement, you can still assign …
Beginners Guide to Creating User-Defined Functions in a Shell Script
Functions in the Shell A function is a set of one or more statements that act as a complete routine. Each function must …
Understanding "$@" and "$*" Positional Parameters in Shell Script
Understanding “$@” and “$*” Positional Parameters in Shell Script The Values of the …
Understanding Korn Shell Arrays
Korn Shell Arrays Arrays are variables that contain more than one value. Don’t declare arrays explicitly or explicitly …
What Is Getopts Statement in Shell Scripts
Processing Script Options With the getopts Statement Options or switches are single-letter characters preceded by a + …
What Is Korn Shell Typeset Statement
Variable Types In the Bourne shell, there are two variable types: strings and constants. In the Korn shell, there are …
What Is "Here" Document in Shell Scripts
The “here” Document Frequently, a script might call on another script or utility that requires input. To run a script …
How to Use File Descriptors to Read From and Write to Multiple Files in Linux
File Input and Output A script can receive input from a file and send output to a file so that the script can run …
How to Write Interactive Shell Scripts
Input and Output in a Script While some scripts run without any interaction with the user, many scripts require input …
The Korn Shell Print Statement Examples
Use the print statement to provide output. Use it wherever you would use the echo statement. It is more versatile than …
CentOS/RHEL: Removing and Adding New Disk, Not Showing Correct Size (EMC Storage)
The Problem Two LUNs of 20 GB were removed and new LUNs of 240GB presented to the server. EMC storage is used.
/Usr/Bin/Chcon: Failed to Create Security Context: : Invalid Argument
The Problem During boot, a message related to SELinux appeared in the console log as shown below: /usr/bin/chcon: failed …
How Cron.allow and Cron.deny Can Be Used to Limit Access to Crontab for a Particular User
In most Linux distributions, access to crontab can be control by accessing two files /etc/cron.d/cron.deny and …
How to Disable High-Resolution Timer in CentOS/RHEL 6
This post introduces how to disable high-resolution timer configured in Linux kernel internally. To disable …
Permission Denied to New User Created While Doing Ssh
The Problem Getting permission denied when we are trying to do ssh to the system using new user created $ ssh user1@[ip …
Beginners Guide to Using "Awk" in Shell Scripts
Introduction to the awk Programming Language The awk programming language grew out of the recognition that many data …
How to Use 'Case' Statement in Shell Script
The case Statement The if/then/else construct makes it easy to write programs that choose between two alternatives. …
How to Use if to Check Command-Line Arguments in Shell Scripts
Positional Parameters The execution of scripts is made versatile by the ability to run a script based on arguments …
How to Write a "USAGE" Message in a Shell Script
When you write a script and set up user interaction, generally the script expects a certain type of user input. For …
How to Stop Brute Force Ssh Attempts in CentOS/RHEL Using Sshd_config, TCP Wrappers and Iptables
You may have seen a large number of login trials in your Linux box, similar to below: Jan 25 01:37:27 [_HOST_] …
How to Use Grep Command in Linux (Along With Regular Expressions)
The grep Command Like most UNIX commands, grep is a mnemonic. The grep mnemonic is derived from ex editor commands. The …
Beginners Guide to Arithmetic Operations on Bourne Shell Variables
The Bourne shell assigns string values to variables only in the assignment statement. The Bourne shell has no built-in …
Beginners Guide to Arithmetic Operations on Korn Shell Variables
Place an integer expression in two pairs of parentheses ((…)) to invoke an Arithmetic evaluation. For …
How to Use Aliases in Ksh Shell
Korn Shell Aliases An alias is a name that you give to a command. You can create an alias in the Korn shell.
How to Use Korn Shell (Ksh) Let Statement
The Korn Shell let Statement The let statement is an alternative to the ((…)) statement. Type the arithmetic …
Understanding Shell Parse Order
Shell Parse Order Parsing controls how a shell processes a command line before it executes a command. A shell has a …
Special Characters and Quoting in Shell Script
Quoting Characters With the exception of the letters and the digits, practically every key on the keyboard is a …
Understanding Shell Variables in Linux
Shell Variables Shell variables are capitalized by convention. The shell maintains two lists of variables: Those local …
Understanding User Startup Scripts - /Etc/Profile, $HOME/.Profile, $HOME/.Kshrc
User Startup Scripts When a user logs in using sh or ksh, configuration scripts run in the following order: /etc/profile …
Beginners Guide to Writing Shell Scripts
Creating Shell Scripts A shell script is a text file that contains a sequence of UNIX commands. The shell script is …
How to Copy Files and Directories to and From Another System in Solaris Using 'Ftp' Command
This section explains how you can transfer files between systems using the File Transfer Protocol (FTP). The ftp command …
How to Integrate CentOS/RHEL 8 Server With Microsoft Active Directory Using Adcli
This post describes how to use adcli to integrate a CentOS/RHEL 8 server into Microsoft Active Directory. 1. Install …
How to Copy Files and Directories to and From Another System With 'Rcp' Command
Copying Files or Directories To and From Another System You can use the rcp command to copy files or directories from one …
How to Use Rlogin, Rsh and Telnet to Login and Run Commands on a Remote Host
Establishing a Remote Login Session A remote login session enables you to access a remote host from your current machine …
How to Compress, Uncompress and View Compressed Files in Linux
The ‘compress’ Command Compressing files helps you to conserve disk space. This section describes how to use …
Is It Safe/Recommended to Disable SELinux?
Disabling SELinux is not a recommended course of action as it is not actually addressing security issues directly. …
Failed to Activate Service 'Org.freedesktop.systemd1': Timed Out (CentOS/RHEL 7)
The problem Failed to start login and other services in the system. /var/log/messages (or journalctl log entry) showing …
How to Disable Oracle Database Auditing
What is Oracle Database Auditing? Auditing is the monitoring and recording of selected user database actions. It can be …
"Test" Command in Linux With Examples
Using the test Command The test command is used for testing conditions. This command is very useful in shell scripts. …
Beginners Guide to Writing Shell Scripts in Linux
Shell Scripts Shell scripts are text files that automate a series of UNIX environment-based commands that otherwise must …
How to Archive Files in Linux Using Tar, Jar
Archiving Files To safeguard your files and directories, you can create a copy, or archive of the files and directories on …
How to Set Alias of a Command in Linux
An alias is a shorthand notation in the Bash shell to enable you to customize and abbreviate UNIX commands. An alias is …
How to Use Functions in Korn Shell (Ksh)
Using Korn Shell Functions Functions are a powerful feature of shell programming used to construct customized commands. …
Protecting File Content During I/O Redirection With Noclobber in Bash Shell
How to use noclobber during redirection to avoid overwriting files Redirecting standard output to an existing file …
Beginners Guide to Performing Basic Process Control in Solaris
Solaris OS Processes Every program you run in the Solaris OS creates a process. When you log in and start the shell, you …
How to Manage Jobs in Bash Shell With Bg, Fg, Jobs Commands
This post describes how to manage jobs in the Bash shell. The Bash shell enables you to run jobs in the background, …
How to Search for Content in Files Using Grep, Egrep, Fgrep
Searching for Content in Files You can search the content of files for either patterns or strings of characters by using …
How to Search for Files and Directories Using "Find" Command in Linux
You can use the find command to locate files or directories in the directory hierarchy. The find command searches using …
How to Migrate /Var to a Dedicated ZFS Dataset on a ZFS Root Pool (Rpool) With Boot Environments in Solaris 10
By default, Solaris 10 installs the Solaris Operating System to a ZFS rpool with a flat filesystem layout. It is …
Why Source and Target Are Not of the Same Size While Using Rsync
Question: While using rsync the source and the target are not of the same size. What could be the reason?
How to Configure Access Control Lists (ACLs) in Solaris
Standard UNIX file protection provides read, write, and execute permissions for the three user classes: file owner, file …
Beginners Guide to Basic File and Directory Permissions in Linux/UNIX
Viewing File and Directory Permissions All files and directories in the Linux OS have a standard set of access …
How to Default File/Directory Permissions Using "Umask"
Every new file or directory has a set of default permissions assigned to it at the time of creation. The user mask …
'Du' and 'Df' Commands Report Different Space Utilization in Linux
Question: The filesystem is almost full. There is a big difference between “df” and “du” …
How to Configure NTP Server and Client in Solaris 10
The Network Time Protocol (NTP) is an internet protocol that is useful to synchronize system clocks to coordinate with …
How to Display Command History in Linux
Displaying the Command History The shell keeps a history of recently entered commands. This history mechanism enables …
How to Use Command Redirection in Linux
Using Command Redirection You can redirect input to and output from commands by using redirection. There are two …
What Is SUID, SGID and Sticky Bit in Linux
In this post, we are going to discuss three special types of permissions that can be set for executable files and public …
Working With Solaris Shell Initialization Files - .Profile, .Kshrc, Cshrc, .Login, .Dtprofile
Working With User Initialization Files This post describes the Solaris 10 OS default initialization files of the Bourne …
Beginners Guide to Printing in Linux
Printing Files You can use the lp command, the lpstat command and the cancel command to submit print requests to a …
How to Copy Files and Directories in Linux Using "Cp" Command
Copying Files and Directories You can copy a file or a directory from one place to another using the cp command.
How to Create and Remove Soft Links (Symbolic Links) in Linux
Files (and directories) might be located on several different file systems. You can use symbolic links to link files that …
How to Create Files and Directories in Linux Using "Touch" and "Mkdir" Commands
You can create new files and directories within the directory hierarchy using the touch and mkdir commands. The touch …
How to Move & Rename Files and Directories in Linux Using "Mv" Command
You can use the mv in linux command to: Move files and directories within the directory hierarchy Rename existing files …
How to Remove Files and Directories in Linux Using "Rm" Command
You can permanently remove files and directories from the directory hierarchy. You can use the rm command to remove files …
How to Use Bash Shell Metacharacters in Linux
Using the Shell Metacharacters Bash shell metacharacters are specific characters, generally, symbols, that have special …
How to Use Korn Shell (Ksh) Variables in Linux
Introducing Korn Shell Variables A variable refers to a temporary storage area in memory. Variables contain: Information …
How to View Directories and Files in Linux - Ls, Cd, Pwd, Cat, More, Tail, Wc
Working With Directories You can use various commands to display the current directory, view the contents of a …
How to Configure a Custom Log File and Location for Rsyslog (Instead of /Var/Log/Messages) on CentOS/RHEL
In some situations or environments, there may be a requirement to configure the rsyslog service to log to a different …
How to Copy User Privileges Between MySQL Servers
Question How to copy user privileges from one MySQL server to another, including: between different versions without …
Beginners Guide to Linux Advanced Intrusion Detection Environment (AIDE)
Introduction What is the Advanced Intrusion Detection Environment (AIDE) utility? AIDE is a small, yet powerful, …
How to Create a Persistent Network Route in CentOS/RHEL 6
Routing is normally configured on routing devices, for example, your standard gateway, however if persistent routers are …
How to Create an Ocfs2 Volume With the Global Heartbeat Feature
Since ocfs2-1.8, global heartbeat feature is available. Earlier versions of OCFS2 had its own heartbeat for each mounted …
How to Set or Query CPU Affinity for Running Processes in CentOS/RHEL 6
This post provides information on how to set or retrieve the CPU affinity of running processes. The …
Beginners Guide to Package Management With YUM in CentOS/RHEL
The purpose of implementing a YUM server is to have a centralized repository of packages/rpms. Also, the main motive …
Useradd Command Examples in Linux
There are several ways in which a user can be added to a Linux Operating System. Here, we discuss the 7 most commonly …
How to Configure DHCP Server in CentOS/RHEL 7
Dynamic Host Configuration Protocol (DHCP) As the name suggests, DHCP is used to control the network configuration of a …
How to Configure ISCSI Target & Initiator in CentOS/RHEL 7
This post will explain how to configure iSCSI target and Initiator configuration in CentOS/RHEL 7. iSCSI is an Internet …
How to Configure Network Bridge in CentOS/RHEL 7 Using Nmcli Command
A Network Bridge is a link-layer device that forwards traffic between networks based on MAC addresses. It learns what …
How to Remove Stale SCSI Devices (SCSI/SAN/ISCSI) Without Rebooting Linux
This post outlines the steps to remove the stale SCSI device from Linux OS without rebooting the server. This topic …
How to Use Man Pages in UNIX/Linux
Using Online Documentation The Linux/UNIX OS provides online manual pages, which describe commands and their usage. …
Beginners Guide to Using the Command-Line Syntax in UNIX/Linux
Constructing and Executing Commands From a Command Line You can use the UNIX system commands to instruct the system to …
Find Command Examples in Linux (Advanced)
I would like to share some useful commands for daily use. Here are some examples. Find command AND Operator By default …
How to Configure Apache Httpd to Provide TLS-Encrypted Virtual Hosts
Transport Layer Security(TLS) Transport Layer Security (TLS) is a method for encrypting network communications. TLS is …
How to Configure Apache Httpd to Serve Dynamic Database-Driven Web Content
Dynamic Content Most modern websites do not consist of purely static content. Most content served out is actually …
How to Use Advanced Intrusion Detection Environment (AIDE) to Monitor Changes in Linux
System integrity is put at risk when configuration files are deleted or modified without authorization or careful …
Beginners Guide to Apache HTTPD
Introduction To Apache HTTPD Apache HTTPD is one of the most used web servers on the Internet. A web server is a daemon …
How to Configure and Troubleshoot Virtual Hosts in Apache HTTPD
In this post, we will learn how to configure Apache httpd to provide IPbased and name-based virtual hosts. Virtual Hosts …
How to Display, Change and Switch Target (Runlevel) in CentOS/RHEL 7 Using Systemd
This post explains how to display, change, and switch target(runlevel) in systemd on a CentOS/RHEL 7 machine. Display …
How to Rotate Systemd-Journald Log in CentOS/RHEL 7
Question: How to rotate systemd-journald log under /var/log/journal/*/ or /run/log/journal/*/? journald logs can be …
Veritas Dynamic Multipathing (VxDMP) Command Line Reference (Cheat Sheet)
The vxdmpadm utility is a command line administrative interface to the DMP feature of VxVM. You can use the vxdmpadm …
How to Backup and Restore MariaDB Database
Creating a Backup It is very important to back up MariaDB databases, and databases in general. The database often …
How to Configure MariaDB Users and Grant or Revoke Database Access Rights
Creating User Accounts with MariaDB By default, MariaDB handles authentication and authorization through the user table …
How to Create and Query MariaDB Database
In this post, we will learn to examine, search, create, and change database information using Structured Query Language …
How to Install and Configure MariaDB on CentOS/RHEL 7
Relational Databases A relational database is a mechanism that allows the persistence of data in an organized way. …
Beginners Guide to Configure SMB Shares in CentOS/RHEL 7
What Is SMB? Server Message Block (SMB) is the standard file-sharing protocol for Microsoft Windows servers and clients. …
How to Perform Multi-User SMB Mount in CentOS/RHEL 7
In this post, we will learn how to mount an SMB share with the multiuser mount option, using password-based …
How to Use "Functions" in Shell Scripts
When used in shell scripts, functions are a way of isolating a segment of code so that it can be called repeatedly …
How to Use Bash Case Statement
Users can add as many elif clauses as they want into an if/then/elif/then/else statement to test as many conditions as …
What Are Bash Startup Scripts - /Etc/Profile, ~/.Bash_profile, .Bash_login, .Profile
One place where environment variables are used is in initializing the bash environment upon user login. When a user logs …
What Are Environment Variables in Linux/Unix
The shell and scripts use variables to store data; some variables can be passed to sub-processes along with their …
Beginners Guide to Configuring ISCSI in CentOS/RHEL 7
Introduction To ISCSI The Internet Small Computer System Interface (iSCSI) is a TCP/IP-based protocol for emulating a …
Beginners Guide to Exporting NFS Filesystem in CentOS/RHEL 7
What is NFS? The Network File System (NFS) is a network file system commonly used by UNIX systems and network-attached …
How to Configure SELinux Labeled NFS Exports
The NFS protocol transmits data in clear text over the network. Furthermore, the server relies on the client to identify …
How to Use Bash if Loops (If Then, if Else Then, if Then Elif Then Else)
Simple shell scripts represent a collection of commands which are executed from beginning to end. Conditional structures …
How to Configure a Caching NameServer in CentOS/RHEL 7
In this post we will explain how to configure a secure, caching nameserver using the unbound DNS server. Caching Name …
How to Configure a Send-Only Email Service in CentOS/RHEL 7
In this post, we will outline steps to configure a CentOS/RHEL 7 server to transmit all emails through an …
How to Configure Postfix Null Client
Postfix is a powerful but easy-to-configure mail server. It is the default mail server in Red Hat Enterprise Linux 7. …
How to Test Shell Script Inputs
To ensure that scripts are not easily derailed by unexpected conditions, it is good practice for script authors to not …
How to Use Exit Codes in Shell Scripts
Every command returns an exit status, also commonly referred to as return status or exit code. A successful command …
How to Use Positional Parameters in Bash Scripts
While user-defined variables provide a means for script authors to create containers to store values used by a script, …
Ultimate Guide to DNS Troubleshooting in Linux
In this troubleshooting post, we will exaplin: Usage of dig command to troubleshoot common DNS problems. Identify …
What Are the Configuration Files for Postfix
Postfix is a powerful but easy-to-configure mail server. It is the default mail server in CentOS/RHEL 7. Postfix is …
Beginners Guide to Writing Bash Shell Scripts in Linux
Many simple day-to-day system administration tasks can be accomplished by the numerous Linux command-line tools …
How to Debug the Shell Scripts in Linux
Inevitably, administrators who write, use, or maintain shell scripts will encounter bugs with a script. Bugs are …
How to Iterate With Bash "For" Loop
System administrators often encounter repetitive tasks in their day-to-day activities. Repetitive tasks can take the …
How to Use Variable in Bash Scripts
As the complexity of a shell script increases, it is often helpful to make use of variables. A variable serves as a …
Understanding Bash Shell Expansion - Command Substitution and Arithmetic Expansion
Aside from variable expansion, the Bash shell offers several other types of shell expansion features. Of these, command …
Beginners Guide to DNS
This post touch bases upon: Explain the hierarchical structure of the Domain Name System (DNS). Differentiate between …
Beginners Guide to Firewalld's "Rich Language Rules"
In this post, we will touch base on how to configure more complex firewall configurations using firewalld’s support …
Beginners Guide to Masquerading and Port Forwarding in CentOS/RHEL 7
Network Address Translatiob(NAT) firewalld supports two types of Network Address Translation (NAT): masquerading and …
Beginners Guide to ZFS Snapshots
This guide is intended to show a new user the capabilities of the ZFS snapshots feature. It describes the steps …
How to Manage SELinux Port Labeling
Selinux Port Labeling SELinux does more than just file and process labeling. Network traffic is also tightly enforced by …
Beginners Guide to Firewalld in CentOS/RHEL 7
firewalld Overview firewalld is the default method in CentOS/RHEL 7 for managing host-level firewalls. Started from the …
Beginners Guide to IPv6 Networking Concepts
In this post, we will touch base on the basic concepts of IPv6 addresses and networking. IPv6 Overview IPv6 is intended …
How to Configure Software Bridges in CentOS/RHEL 7
This post outlines steps to configure and troubleshoot local software bridges and associated interfaces. Software Bridges …
Understanding Early Debug Shell, Emergency and Rescue Targets in CentOS/RHEL 7
If there are problems during the starting of services, there are a few tools available to system administrators that can …
How to Configure IPv6 Networking in CentOS/RHEL 7
This post will touch base on how to configure IPv6 networking using nmcli and configuration files in the …
How to Configure Network Teaming in CentOS/RHEL 7
In this post, we will outline the steps to combine two network links using network teaming to provide link redundancy or …
How to Configure Networking Using Nmcli and Configuration Files in CentOS/RHEL 7
In this post we will explore the IPv4 networking using nmcli and configuration files in the …
How to Manage (Troubleshoot) Network Teaming in CentOS/RHEL 7
In the last post, we have seen how to configure the network teaming in CentOS/RHEL 7. In this post, we will see the …
Beginners Guide to Systemd Targets (Runlevels)
What is a systemd Target In SysVinit systems, you had a defined but configurable set of runlevels numbered from 0 to 6.
How to Recover Lost Root Password in CentOS/RHEL 7
Recovering the** root** password is a trivial task while still logged in as an administrator or a user with full sudo …
Beginners Guide to Systemd
System startup and server processes are managed by the systemd System and Service Manager. This program provides a …
Understanding Inter-Container Communication for Docker
In most of your current architectures, you probably separate your Web Server from your Database (virtual) server. This …
How to Search, Pull, List and Run a Docker Container
Containers enable you to package an application with all the components it needs, such as libraries and other …
How to Enable or Disable Ip_forwarding in Solaris 10 and Prior
A number of factors affect how IP forwarding and routing is configured at boot time. Prior to Solaris 10, IPv4 …
How to List or Install Only Security Updates in CentOS/RHEL 6 and 7
Question: Is it possible to limit yum so that it lists or installs only security updates? How to patch the system only …
How to Create LVM Filesystem Using Disk Partitions in Linux
Running out of disk space and having to provision new storage is something that cannot be overlooked in infrastructure …
How to Reduce LVM Filesystem in Linux
Unlike growing the filesystem, reducing the filesystem should be practiced carefully. In the example below, we will see …
"ORA-00911: Invalid Character" - Error While Dropping or Renaming Tablespace Due to Junk Chracters
The Problem Not able to drop or rename a tablespace which is having junk characters in the name. For example:
How to Use Setenforce Command to Change SELinux Modes
SELinux Modes SELinux can either be in an enabled or a disabled state. In order to check in which state it is running, …
Uniq Command in Linux
The uniq command can be used to remove the duplicate lines from a text file in Linux or Unix. The duplicate lines should …
How to Find Large Files in Linux
Filesystem alert! We all hate to get full-filesystem alerts, especially at quitting time on Friday when the developers …
How to Find NFS Version
Network File System (NFS) is one of the native ways of sharing files and applications across the network in the …
Ln Command Examples to Create Soft and Hard Links
ln is the Linux command that allows you to create links. For understanding purposes, you can compare this to the windows …
Managing Docker Containers
Docker is OS-level virtualization software for developers and sysadmins, the beauty of docker is that it creates an …
Rootsh Installation on Ubuntu 18.04/16.04 LTS
Rootsh is a tool from which you can log your user activity in plain-text, so all the activities that are performed by …
How to Monitor a Chown or Chmod Command in CentOS/RHEL
The Ask The directory/file ownership and permissions are getting changed by unknown users. How can we track these …
How to Reset MySQL Root Password
Question: We have forgotten the MySQL database root password. How can we reset it? MySQL stores all its username and …
How to Disable/Enable Echo of Keys/Commands Typed in Linux Shell
Question: How to hide commands typed in a Linux terminal? How to make passwords invisible while they are typed in Linux …
What Are the Different File Types in the Linux System
The Linux file system is distinct from the file systems of other operating systems because of the various file types. …
"Tty" Command in Linux With Examples
The term tty is short for teletypewriter, the terminal device that UNIX was first run from. The tty command writes to …
Difference Between Find and Locate Command in Linux
In Linux there are many methods by which a user can locate files and directories. Two of the most popular utilities for …
Understanding Octal Permission Bits in Linux
As a user of a system, to access a file in Linux and UNIX, it is important that a user has the required permission for …
What Is the Correct Permission for /Tmp Directory in Linux
The /var/tmp directory is made available for programs that require temporary files or directories that are preserved …
Oracle Interview Questions - Datafile Autoextend Feature
This post aims to provide basic oracle database interview questions for the Datafile Autoextend feature. 1. How to know …
Veritas Infoscale Availability (VCS) CommandLine Reference (Cheat Sheet)
VCS Operations Task Command Start VCS hastart Start VCS stale hastart -stale Force start VCS hastart -force Start VCS on …
"Rm" Command Examples in Linux
The rm command is used to remove (delete) files and directories in Linux. rm (remove) deletes a file permanently, and …
How to Remove Files and Directories in Linux
Linux includes two commands that you can use to delete files and directories: rm (remove) and rmdir (remove directory). …
Understanding SMCO (Space Management Coordinator) Background Process in Oracle Database
The post dives into the basics of SMCO (Space Management Coordinator) Background Process in Oracle 11g and how to enable …
How to Manage Order of Mounting in CentOS/RHEL 7,8 Using Systemd
CentOS/RHEL 6 and earlier versions, were mounting the filesystems in an order defined in the file /etc/fstab. But the …