Debugging in Shell Script

What is Shell?

The UNIX shell program interprets user commands which are either directly entered by the user, or which can be read from a file called the shell script or shell program. Shell scripts are interpreted, not compiled. The shell reads commands from the script line per line and searches for those commands on the system.

The below command is used to check known shells in a UNIX system.

root@localhost$ cat /etc/shells 
# List of acceptable shells for chpass(1).
# Ftpd will not allow users to connect who are not using
# one of these shells.

/bin/bash
/bin/csh
/bin/dash
/bin/ksh
/bin/sh
/bin/tcsh
/bin/zsh

To change the shell, just write down the shell name; since a shell is an executable file (program), the current shell activates it and it gets executed. A new prompt is usually shown because each shell has its typical appearance.

Continue reading “Debugging in Shell Script”

Proc File System in Linux

I’d like to share an interesting finding with you today. Perhaps, many of you must be already familiar with it but being a newbie, it really intrigued me.

I have recently enrolled myself in the DevOps Ninja program conducted by my organisation- OpsTree. Everything that I’m learning here is new to me and often amuses me. One day, I was working on an assignment and executed the top command. I left the task as it is and meanwhile started browsing something on the internet. Suddenly a question struck my mind that from where the top command fetches its data ( you can see how I got digressed from my main assignment :p).

Continue reading “Proc File System in Linux”

That’s Why Iptable Is Not A Good Fit For Domain Name?

Context

Let’s first talk about how it all started with and what we achieved.

It’s all started with a healthy discussion with a team where our team members were discussing many aspects of different fields of technology. So, one of our colleagues mentioned OpenVPN. So, we discussed the different working field, architecture, workflow of OpenVPN, in which role of iptables comes into the picture because for Linux architecture, OpenVPN support iptables as it’s primary firewall utility or can say OpenVPN support iptables as it’s a firewall for filtering workflow.

So in-between discussion, I mentioned that I am using iptables in OpenVPN to block traffic for the domain name and it is working fine. So, my colleague asked me about how you implemented & how is it possible to use iptables for domain and they discussed multiple logical explanations like OSI layer support and many other things. So, we decided to do POC of this discussion and try to write-up some blog or points to make clear that is it possible use iptables for the domain name and if not, what are the area that we can cover with iptables for the domain name and try to cover up flaws of this. Continue reading “That’s Why Iptable Is Not A Good Fit For Domain Name?”

Linux OS Hardening: CIS Benchmarks

As we’re going through a pandemic majority of business have taken things online with options like work from home and as things get more and moreover the internet our concerns regarding cybersecurity become more and more prominent. We start to dig a little to have standards in place and terms like  Compliance, Hardening, CIS, HIPPA, PCI-DSS are minted out. Today we’ll be discussing why to have CIS benchmarks in place in the least and how we at Opstree have automated this for our clients.

Before moving forward get familiar with basic terms:

CIS Benchmarks are the best security measures that are created by the Centre of Internet Security to improve the security configuration of an organization. Continue reading “Linux OS Hardening: CIS Benchmarks”

Create Your Own Container Using Linux Namespaces Part-1.

In this lock-down, everyone has to maintain a social distance and in this trying time, we can learn from docker to isolate ourselves. So before that, we need to learn how docker does it?
The best approach to learn is to simulate it. For that, we’ll be creating our own container tool for the application to isolate itself.

Self isolation | SpongeBob SquarePants | Know Your Meme

 

Continue reading “Create Your Own Container Using Linux Namespaces Part-1.”