The Uncomplicated Firewall (UFW) is a firewall management tool that makes it easier to configure the iptables service. UFW originated with Ubuntu® but can be downloaded and installed on other distributions. It is primarily useful for home users who don’t have experience with the intricacies of firewall configuration. The ufw command enables you to work […]
Archives for March 2022
How to use ipset Command in Linux
IP sets are stored collections of IP addresses, network ranges, MAC addresses, port numbers, and network interface names. The iptables tool can leverage IP sets for more efficient rule matching. For example, let’s say you want to drop traffic that originates from one of several IP address ranges that you know to be malicious. Instead […]
Introduction to Array in C Programming
An array is a collection of similar data elements. These data elements have the same data type. The elements of the array are stored in consecutive memory locations and are referenced by an index (also known as the subscript). If one subscript, then we call a one-dimensional array. Memory representation in an array The array […]
C Programming Basics – Interview Questions
1. What is Token? A token is a building block of a program. A C program consists of various tokens and a token is either a keyword, an identifier, a constant, a string literal, or a symbol. 2. What is Keyword? Keywords are special reserved words associated with some meaning. 3. What is keyword auto […]
Basics of C programming
Structure of C Program A C program is divided into different sections. There are six main sections to a basic c program. The six sections are: Documentation Link Definition Global Declarations Main functions Sub programs The whole code follows this outline. Each code has a similar outline. Now let us learn about each of these […]
How does the RMAN Retention Policy Obsolete Incremental Backupsets
The report/delete obsolete commands works in two steps. First, we identify the oldest full backup (i.e. full or level 0 backupset, or image copy) of every file that is not obsolete, as defined by the retention policy (either REDUNDANCY or RECOVERY WINDOW). Every older full backup is obsolete. Then, all archived logs and level > […]
How do we Set A Retention Policy For Tape Backups And Disk Backups Differently
Question: How do we Set A Retention Policy For Tape Backups And Disk Backups Differently? For example, setting the tape retention policy to 14 days while setting it to 3 days for the disk backups. Step 1: Set the retention policy. RMAN currently only allows one retention policy. The retention policy should be set to […]
‘error opening class fc_host’ – systool Command Error on CentOS/RHEL 7 and 8
The Problem When running the systool command on CentOS/RHEL 7, the following error message is reported: # systool -c fc_host -v Error opening class fc_host The Solution The error occurs because the scsi_transport_fc module that is responsible for populating the contents of /sys/class/fc_host/ directory is not loaded on the system. 1. Manually load the scsi_transport_fc […]
How to Check if a table is Indexed in Oracle
Understanding ‘Why my index is not being used?’ is a big topic as there are many varied reasons for indexes not being used. The first thing you can do is to check whether your table is indexed or not. Why SHOULD the index be used? Oracle does not have to use an index simply because […]
Dependency failed for NFS server and services
The Problem Attempting to start the NFS (nfs-server.service) on CentOS/RHEL 7 fails as follows: # systemctl status nfs-server.service nfs-server.service – NFS server and services Loaded: loaded (/usr/lib/systemd/system/nfs-server.service; enabled; vendor preset: disabled) Drop-In: /run/systemd/generator/nfs-server.service.d ‘-order-with-mounts.conf Active: inactive (dead) Mar 09 16:17:10 hostname systemd[1]: Dependency failed for NFS server and services. Mar 09 16:17:10 hostname systemd[1]: nfs-server.service: […]