Linux links

This page by David Papkin contains useful Linux links

List of Linux distributions

Best Linux Distributions That are Most Suitable for Beginners

10 of the Most Popular Linux Distributions Compared

10 Best and Most Popular Linux Desktop Environments of All Time

The Difference Between Fedora, Redhat, and CentOS

What is the relationship between Fedora and Red Hat Enterprise Linux?

Red Hat and the CentOS Project Join Forces to Speed Open Source Innovation

Understanding the Color Code of Linux files

The CentOS Project

Linux and the GPL

GNU General Public License (GPL) v2.0

Is Linux kernel free to modify?

enable selinux

How to change runlevel on Centos 7

Learn Linux, 101: Runlevels, boot targets, shutdown, and reboot

Writing Shell Scripts

What’s the version of my OS?

Check what Debian version you are running on your Linux system

Setup Local Yum Repository on CentOS / RHEL / Scientific Linux 6.4


Linux Bare Metal Restore info

Bare Metal Restore

Notes of bare metal recovery

55187 Linux Backup lab by David Papkin


CentOS / Redhat Iptables Firewall Configuration Tutorial

Ubuntu Basic iptables howto

Ubuntu Iptables: How to Control Network Traffic Using iptables?

Graphical Admin tools

How to Install Webmin on CentOS 7

How to Install Latest Webmin on Debian 10/9/8

Web-based interface for system administration


How To Check For Open Ports in Linux With netstat, lsof And nmap

See Bandwidth Usage Per Process With Nethogs Tool

How to Monitor Network Traffic using nethogs

NetHogs – Monitor Per Process Network Bandwidth Usage in Real Time



What happened to eth0? Predictable Network Interface Names

How can I change the default “ens33” network device to old “eth0” on Fedora 19?

Change default network name (ens33) to “eth0” in Centos7/RHEL7

How to change a network interface name on CentOS 7


Ultimate guide to linux patch management

Patch Management Best Practices

10 Linux Hardening & Security Best Practices

40 Linux Server Hardening Security Tips [2021 edition]

Software packages

How To Set Up Local Yum Repositories On CentOS 7

CentOS / RHEL : How to create and host yum repository over httpd

Configuring Yum and Yum Repos (REDHAT Docs)


GRUB 1 bootloader – Full tutorial

GRUB 2 bootloader – Full tutorial

Linux FHS

Understanding File System Superblock

Redhat LVM management

Linux LVM Logical Volume for CentOS 7 / RHEL 7

You can monitor RAID devices multiple ways as in:

$ sudo mdadm --detail /dev/md0
$ cat /proc/mdstat

One can also use mdmonitor which requires configuring /etc/mdadm.conf.

The command:

$ sudo mdadm --detail /dev/mdX

will show the current status of the RAID device /dev/mdX. Another way to do this is to examine the /proc filesystem: 

$ cat /proc/mdstat

User Mgmt

Gecos field


Linux and the GPL

GNU General Public License (GPL) v2.0

Is Linux kernel free to modify?

What’s the version of my OS?

How to Configure ACL(Access Control Lists) in Linux FileSystem

NTUC evaluation

Q & A

 Q How to check resource usage for a server twice per hour?

vmstat 1800 2

How to tell the status and current Raid level of your Linux software RAID array?

sudo bash -c mdadm –detail –scan 

cat /proc/mdstat


How to list logical device in Logical Volumes in lv012?


lvdisplay -v /dev/vg00/lvol2


How to check a physical volume that is using Logical Volume Manager?


pvdisplay /dev/ssd3

Q How to show the usage of process that are consuming network bandwidth?

a) You can use the nethogs utility. 

ex nethogs -a


nethogs -i ens33 or whatever interface you want to get usage stats from.

b) you can use vnstat  utility

vnstat -i ens33

vnstati -s -i ens33 -o vnstatreport.png

How to know what ports a server is listening to?

A lsof -i -P -n | grep LISTEN

How to see what active connections from the Internet?

A netstat –listen

Q How to use iptables  

a) Display Your Firewall status

iptables -L -n -v

 b) Display firewall with line numbers

iptables -n -L -v –line-numbers

c) Display INPUT or OUTPUT chain rules

iptables -L INPUT -n -v
iptables -L OUTPUT -n -v

d) Stop / Start / Restart the Firewall

service iptables stop/start/restart

e) Drop all incoming / forwarded packets, but allow outgoing traffic

iptables -P INPUT DROP
iptables -P FORWARD DROP
iptables -A INPUT -m state –state NEW,ESTABLISHED -j ACCEPT
iptables -L -v -n


Linux System Administration (SF)_AR_V2.0

Linux System Administration (SF)_LG_Supplement_V2.1

6 Steps to Assess your Network Security

Follow these six steps to assess the vulnerability of your network:

Step 1: Identify and understand the way your business is organized and operates

  • Most businesses rely on collaboration between representatives from their internal business units, legal teams, and finance departments to coordinate with IT professionals regarding their exact network needs. Consider issues such as client or customer privacy, regulatory compliance, business processes, and competitive positioning within your industry.

Step 2: Locate the applications and data that are used during the business process

  • Identify which of these are sensitive and what information is at risk in the event of a privacy breach.

Step 3: Search for hidden data sources that may allow easy access to secure information

  • This is especially important if there is cloud-based access to private data or access across multiple platforms, including smartphones and tablets.

Step 4: Identify both virtual and physical servers that run applications necessary for your business operations

  • These servers may not be protected and may allow access to sensitive information without you knowing it.

Step 5: Keep track of what security measures are already in place

  • Your network protection may already include specific policies, firewalls, virus detection, VPNs, disaster recovery, and encryption. It’s important to understand the capabilities of your current security measures in order to properly address any vulnerabilities.

Step 6: Scan your network for vulnerability

  • The results of this scan will give you confirmation of your network’s security. Should a virus or vulnerable area be identified, you will need to develop a network security strategy, possibly with the help of an MSP.

4 steps of RIsk managment

  • Step 1: Identify hazards. Examples of common hazards which can lead to musculoskeletal disorders (MSD) …
  • Step 2: Assess the risk. …
  • Step 3: Control the risk. …
  • Step 4: Review risk control.

Threat Modelling techniques














Threat Modeling: 12 Available Methods

STRIDE Threat Modeling (Developer Focused)

STRIDE stands for Spoofing Tampering Repudiation Information Message Disclosure Denial of Service and Elevation of Privilege. Microsoft’s threat modeling methodology – commonly referred to as STRIDE  – aligns with their Trustworthy Computing directive of January 2002.[4] The primary focus of that directive is to help ensure that Microsoft’s Windows software developers think about security during the design phase.

P.A.S.T.A. Threat Modeling (Attacker Focused)

The Process for Attack Simulation and Threat Analysis is a relatively new application threat modeling methodology.[3] PASTA threat modeling provides a seven-step process for risk analysis which is platform insensitive. The goal of the PASTA methodology is to align business objectives with technical requirements while taking into account business impact analysis and compliance requirements. The output provides threat management, enumeration, and scoring.

The Visual, Agile, and Simple Threat modeling (VAST) methodology was conceived after reviewing the shortcomings and implementation challenges inherent in the other threat modeling methodologies. The founding principle is that, in order to be effective, threat modeling must scale across the infrastructure and entire DevOps portfolio, integrate seamlessly into an Agile environment and provide actionable, accurate, and consistent outputs for developers, security teams, and senior executives alike.

Trike Threat Modeling (Acceptable Risk Focused)

IS Standard and Frameworks







Linux Authentication: PAM Tool






Asset Threat Risk Vulnerability







Risk Assessment and Cost Benefiyt Analysis








What are some Risk Identification tools and techniques?


Risk Identification tools and techniques



What is CIA Triad?


What is CIA Triad ?

Name some Linux Security Tips and Checklist









Update debian dpkg to use old archives 

sudo nano /etc/apt/sources.list

change us.archive to old-releases.

Ex deb cosmic main


deb cosmic main