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 […]
Archives for March 2022
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 […]
‘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 […]
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: […]
How to Change Default Port of Apache On RHEL/CentOS 7
If you want to change Port in the Apache configuration file it’s easy to do. You can also run a website on a different port rather than the default port. 1. Let’s check which is listening to which service: # nmap -sT -O localhost 2. Check whether Port 8000 is free or not: # lsof […]
EFS Mount Issue “Failed to resolve server: Name or service not known”
The Problem mount.nfs4: Failed to resolve server fs-d3d54350.efs.us-east-1.amazonaws.com: Name or service not known or: ping: unknown host fs-d3d54350.efs.us-east-1.amazonaws.com The Solution 1. Open the Amazon VPC console. 2. Select the VPC. 3. Review the information in the Description tab. In this example, both settings are enabled. DNS resolution Enabled DNS hostnames Enabled 4. To update these […]
How to take mailbox backup of Zimbra Account from CLI
A system administrator’s worst nightmare is the call, page, text message, or any other alarm informing you that the server is down. Especially when the server is very critical and instrumental to the organization, like a Zimbra Mail Server. This post discusses the backup and restores procedure of a Zimbra Account. Mailbox backup from CLI […]
How to Disable/Enable services in Zimbra Mail Server
Zimbra provides open-source server and client software for numerous applications like messaging and collaboration: email, group calendaring, contacts, and web document management and authoring.The Zimbra server has been made available for various platforms like Linux, Mac OS X, appliances, and virtualization platforms. The Zimbra Web 2.0 Ajax client runs on the most commonly used browsers […]