I Wish I Had Read These 29 Things Before I Started Programming

Programming is not an easy career. With many people graduating each year from top computer science programs in the country, it’s one of the most competitive careers anyone can embark on. At the same time, a programming career is exciting. With the advancement of technology, every day, there are innovations in the industry. Programming becomes a passionate endeavor for those who love it.

When I started as a programmer years ago, I wish someone sat me down and told me everything on this list. This list can save any new programmer a lot of headaches and energy. This list can be the one you refer to as your programming career progresses. Even if some of these points might not be relevant for you right now, one day you will see the wisdom in them.

As a programmer, you are at the cusp of greatness.

You just have to venture on with a little bit of knowledge about your path.

1. You Don’t Need a Degree to Program, but You Do Need the Knowledge

I worked with many programmers who didn’t graduate with a computer science master’s degree or an undergraduate degree in computer science. Programming is one of the few careers you can have that doesn’t depend on a degree. However, programming is a knowledge-intensive career. You have to read those ten essential books if you’re going to start a career in programming. These ten books will cover the essential concepts of computer science as well as how to work on project teams. Setting a firm foundation for your technical skills, with a solid understanding of the basic concepts, on top of writing functional code, will enable you to ace technical interviews and communicate with your co-workers.

2. Programming Takes Creativity on Top of Problem-Solving Skills

Most people have the preconception that programming is all about analytical and problem-solving skills. That is partially true. Programming also involves a lot of creativity. Often, there are many ways to write a given piece of code. The creativity comes when you devise ways to code most simply and effectively.

3. You Can’t Learn Everything There Is to Learn. The Trick Is to Learn a Few Things Very Well

There are hundreds of programming languages out there. There are areas of programming that pave the way for particular career paths: web developer, front-end developer, back-end developer, software engineer, database developer, etc. Decide what kind of developer you want to be, then learn all the technologies and skillsets needed for that particular position.

4. You Don’t Need to Be a Robot. It’s Better If You Are Human

Remember you are a human first and a programmer second. It’s easy to get lost in your code when you first start to program. There are days when I don’t leave my computer until I’ve completed all the milestones of my project. But you are a human being; you need to laugh, cry, de-stress and talk to people. By managing your life to maximize fun and excitement outside of work, you will bring more creativity into your work as a programmer.

5. Programming Is All About Applying Knowledge. It’s Not About Memorization

Unlike research, where you are inventing and creating new areas of knowledge, programming is all about applying existing knowledge. Books, research papers, online articles, and learning videos become resources that you will use often. There’s no need to memorize anything. You can always reach for a resource to find the answer. Memorization comes automatically and naturally as you work on more projects.

6. You Will Deal With Imposter Syndrome Every Day

Programming is the one career all the “smart” people seem to gravitate towards. Unless you are a genius, you will, like I do, experience imposter syndrome every day. When you experience it every day, you tend to figure out a way to deal with it. For me, I’ve always used it as motivation to learn new things. I’ve learned to put it into perspective and just be content at improving a little bit each day.

7. You Have to Have a Life Outside of Being a Programmer. Otherwise, You’ll Just Be Addicted to Programming

There will be times when you are a hermit at home. However, to be a happy programmer, you have to proactively seek a life outside your computer screen. Often the success of your career depends on the people you meet. Networking is essential when you are a programmer. Having a personality outside of being a programmer is essential to keep yourself from being addicted to programming. When you can enjoy your passions without being compelled to do it, your best work comes out.

8. You’ll Learn Programming Faster If You Pair Program With Someone

At the beginning of your career, you’ll be tempted to close your door to the world and read those ten books on programming to build your computer science foundations. Guess what? You learn much faster if you find a buddy. I’ve gone through programming books in half the time working on a project with a buddy. When you pair program with someone, all your programming “warts” come out. Your code will be critiqued. You will learn to write efficient code because someone else is watching. You will want to find out the best way to do things because your buddy is learning too. When you work as a programmer, someone’s always reviewing your code. You are never programming alone. It’s time to get used to that.

9. You Don’t Need to Be Good at Math and Science

In the technology industry, you will meet all kinds of superstar programmers who found the logical thinking aspect of programming appealing after a lifetime of liberal arts education. There are plenty of painters and writers who make a living programming while pursuing art on the side. All you need to be a good programmer is persistence. Programming is hard work. But once you have that, anyone can go through programming books and pick up the basics. There are plenty of people who pick up math after working in the industry for a while. Eventually, these people can even understand complex algorithms and implement them without any kind of formal math education.

10. You Need to Be an All-Star “Learner”

A programmer is a master learner. You might not start out being a master learner. But you will get there. Sometimes your workplace will ask you to pick up three programming languages in six months. That’s the state of technology innovation. As programmers, we learn every day. Learning is like breathing. If you are uncomfortable with learning every day, you will be forced to get used to that.

11. You Will Obsess About Finishing Your Projects

Coding addiction is a real thing. At some point in your programming career, you will experience all-night programming marathons. You won’t want to go to sleep until you’ve finished your milestones. You’ll forget to eat, drink, or even get up from your desk because your brain is processing so much information. That is okay. Once you are done, take a walk outside. Go on vacation.

12. You Will Spend All Day Looking for One Tiny Bug

Most of the time, on programming projects, many pieces are interdependent on one another. Often, you will find that you cannot move on unless you’ve fixed one tiny bug that’s been lurking in your system. As a programmer, you will stress about the entire project unless you find this bug. You will sit at your computer all day looking for it. You will dream about the code at night until you find it.

13. You Will Spend Most of Your Time Googling for Answers That No One Can Answer for You

If you program in a popular language, you’ll be able to find the answers to most of the problems you encounter online. However, there are exceptions. Sometimes, no one has encountered the problems you bumped into. In this case, referring to programming books and asking around on programming boards often will point you in the right direction.

14. You Will Read a Design Pattern Book

It doesn’t matter if you graduated from the best computer science program in the country. There comes a time in every programmer’s career that you will sit down and read Head First Design Patterns from cover to cover. It’s probably one of the most read books for a new programmer. So, what are you waiting for? Pick it up and read it from cover to cover.

15. You Will Learn to Obsess About the Exact Spelling

At some point in every programmer’s career, you will have written enough code in your favorite language to want to do things your way. This includes the exact spelling of naming conventions that you give to your variables, your classes, and even the tables in your databases. You will scrutinize this to no end. The last thing you want is some bug that crept up because you misspelled a name. Remember, it’s okay to obsess about things if you have a good reason for it. When you don’t have a good reason for it, it’s just repetitive behavior.

16. You Will Give Up

How many times have I given up? I can’t even count. Sometimes you just bump into problems you can’t solve. Sometimes it gets so difficult that you just want to quit. Sometimes work environments make you want to quit. Your passions depend on your persistence. This is when you are tested. Are you here to stay or are you going to go? I always came back. Sometimes, after a few years of not programming a single line, I always came back as a new person ready to tackle a project. This is when you know you love your work. It’s when it becomes a home, a springboard for your adventures.

17. You Will Restart

If you believe in higher powers, you will be able to relate to this. Each time, when I see people come back to programming, it’s never about the money. It’s always for the love of programming. When you see someone who enjoys programming like you used to, you are envious. You can’t let it go. Then, suddenly, you are back pursuing a project. You know in your core that you live and breathe code. This is when you know that you are a true programmer.

18. You Will Go Back to Some Form of School to Learn the “Correct” Way of Doing Things

Even the best programmers graduating from elite computer science master’s programs will continue their education at work. In fact, on the job training is one of the best perks of working for large technology companies. Companies will send you on “expensive” courses and seminars to train you in the latest technologies they want you to use. If by chance, you’re still not learning enough at work, you will reach out to the many online coding academies and youtube videos to sharpen your skillsets.

19. You Will Be Hired by Someone You Don’t Want to Work For

Even if you are a mediocre programmer, there will come a time when certain companies will need your skills. When they are interviewing you, try to remember that you are interviewing them too. Depending on the company’s culture, you might find yourself wanting to say “no” to a cushy package. As a programmer, you will work long hours. It’s almost critical to find a company culture that you can fit into. Happiness leads to better work. If your skills are in demand, other companies will knock on your door. Please do not settle unless it’s necessary.

20. You Will Flunk a Technical Interview

Technical interviews are no joke. Senior programmers often make up technical interview questions for fun. Often, these questions are extra difficult for a reason. If you flunk the technical interview, it’s not the end of the world. It certainly does not say anything about your programming abilities. It only tests your knowledge base. Try to look on the bright side. If your people skills shine, managers will remember you. If they like you and you are not a fit for this role, they might still call you for another position.

21. You Will Be Told That You Are Great

At times in your career, you will feel like you are a star. Managers who depend on you to complete their projects will tell you how great you are to motivate you. You will feel like you are on top of the world. Remember that they are appealing to your ego. Stay grounded. There are always new technologies to learn. There are always new programmers who are better than you.

22. You Will Be Told That You Don’t Know Anything

At times in your career, you will feel like you don’t know anything. Someone who is frustrated with the project will make it a point to tell you that you don’t know anything. Perhaps they do this to put you in your place. But, since you are reading this, you will take it in stride. Because you probably know a lot more than you think you do. Each day that passes, you will learn a little more than the day before. After a year, people will look up to you. Keep at it. After some time, you may even gain the respect of the person who told you that you don’t know anything.

23. You Will Want to Compete With Other Programmers Who You Admire

One of the most awesome aspects of programming is competition. I love programming with people who I admire. When you can write code that a programmer you admire deems worthy, you will feel like you just won the lottery. Competition in programming is always in good fun. It’s not about who’s the best. It’s more about learning from each other.

24. You Will Not Understand a Word That Your Coworkers Just Said

In the beginning, this may happen once a week or once a month. At your new programming job, you will not understand what your coworker just said. This could be for two reasons. For the life of you, you just can’t get your head around their accent. In this case, ask another coworker to translate. There’s no shame in not being able to understand someone’s speech. Chances are, it took other coworkers years to get used to the accent too. The other reason is that what your coworker just said went completely over your head. That is also okay. After all, your coworker is the expert. Ask your coworker to explain it all in picture form. You’re going to want to pull up a chair for this. Chances are, it might take a while.

25. You Will Feel Shame Looking at the Spaghetti Code You Wrote Last Year

This happens all the time. I was criticized for my Perl code when I started. It was well-documented code that’s designed well, too. But I wrote it in a language that was difficult to read. So, I wrote the spaghetti code. But, each year, no matter how hard I try, I still find some spaghetti code that I whipped up quickly to get a job done. That’s what programmers do. We fix things and we patch things up. There’s no shame in that. When you realize that it’s you who wrote it, just step back and fix it if you can.

26. You Will Take Shelter in Your Database Projects When You Are Too Sick to Look at Another Line of Code

This happens when you’re on a nice programming trek up the mountain. It’s been two months. You need a break. But you love the momentum so you keep going. Then you realize that SQL is fun. You can’t figure out why you can’t look at another line of code. But somehow, putting data into the database and getting it out is now a joyful event. You revel in the simplicity of a completely logical language.

27. You Will Both Love and Hate Hackathons

Hackathons are common these days. Programmers get into teams and compete with each other. In the process, it’s intense learning in a few hours. You will love the hackathons for the camaraderie. You will hate it for the carpal tunnel syndrome that you developed while typing at top speed. You will also hate it for the crowded rooms that you work in and the sensory overstimulation that you receive during the event.

28. You Will Think You Don’t Understand a Word of English While Reading Research Papers

Do you speak English? Well, most people will say yes. But, I guarantee you that you will read some research paper over and over again and realize that it’s way over your head. For me, most of the research papers on algorithms seemed like a giant forest before I learned the foundations of college math. Then, suddenly, it all seemed to make sense.

29. You Will Buy Headphones

At some point in your career, you will realize that any kind of noise impedes your senses when you’re intensely focused on your code. Having good headphones that will cancel out external noise will allow you to work in crowded rooms with focus. At some point, you will also find that music helps you to code. I found out early in my coding career that the rhythm in music helps me code fluidly. Even now, I reach for some music when I need to be productive.

You may also like: 7 Skills of Highly Effective Programmer for Developers.

In hindsight, I’m actually really happy that I was so naive in the beginning. Knowing so little back then gave me the motivation to think critically about everything I learned later on.

Now I get to spend time helping other people achieve their goals through code. What could be better than that? Share what you think.

Happy coding !

#Programming #Coding #Learn To Code #Development #Education

What is GEEK

Buddha Community

How To Secure A Linux Server

An evolving how-to guide for securing a Linux server that, hopefully, also teaches you a little about security and why it matters.

Introduction

Guide Objective

This guides purpose is to teach you how to secure a Linux server.

There are a lot of things you can do to secure a Linux server and this guide will attempt to cover as many of them as possible. More topics/material will be added as I learn, or as folks contribute.

(Table of Contents)

Why Secure Your Server

I assume you're using this guide because you, hopefully, already understand why good security is important. That is a heavy topic onto itself and breaking it down is out-of-scope for this guide. If you don't know the answer to that question, I advise you research it first.

At a high level, the second a device, like a server, is in the public domain -- i.e visible to the outside world -- it becomes a target for bad-actors. An unsecured device is a playground for bad-actors who want access to your data, or to use your server as another node for their large-scale DDOS attacks.

What's worse is, without good security, you may never know if your server has been compromised. A bad-actor may have gained unauthorized access to your server and copied your data without changing anything so you'd never know. Or your server may have been part of a DDOS attack and you wouldn't know. Look at many of the large scale data breaches in the news -- the companies often did not discover the data leak or intrusion until long after the bad-actors were gone.

Contrary to popular belief, bad-actors don't always want to change something or lock you out of your data for money. Sometimes they just want the data on your server for their data warehouses (there is big money in big data) or to covertly use your server for their nefarious purposes.

(Table of Contents)

Why Yet Another Guide

This guide may appear duplicative/unnecessary because there are countless articles online that tell you how to secure Linux, but the information is spread across different articles, that cover different things, and in different ways. Who has time to scour through hundreds of articles?

As I was going through research for my Debian build, I kept notes. At the end I realized that, along with what I already knew, and what I was learning, I had the makings of a how-to guide. I figured I'd put it online to hopefully help others learn, and save time.

I've never found one guide that covers everything -- this guide is my attempt.

Many of the things covered in this guide may be rather basic/trivial, but most of us do not install Linux every day and it is easy to forget those basic things.

IT automation tools like Ansible, Chef, Jenkins, Puppet, etc. help with the tedious task of installing/configuring a server but IMHO they are better suited for multiple or large scale deployments. IMHO, the overhead required to use those kinds of automation tools is wholly unnecessary for a one-time single server install for home use.

Other Guides

There are many guides provided by experts, industry leaders, and the distributions themselves. It is not practical, and sometimes against copyright, to include everything from those guides. I recommend you check them out before starting with this guide.

• The Center for Internet Security (CIS) provides benchmarks that are exhaustive, industry trusted, step-by-step instructions for securing many flavors of Linux. Check their About Us page for details. My recommendation is to go through this guide first and then CIS's guide. That way their recommendations will trump anything in this guide.
• For distribution specific hardening/security guides, check your distributions documentation.
• https://security.utexas.edu/os-hardening-checklist/linux-7 - Red Hat Enterprise Linux 7 Hardening Checklist
• https://cloudpro.zone/index.php/2018/01/18/debian-9-3-server-setup-guide-part-1/ - # Debian 9.3 server setup guide
• https://blog.vigilcode.com/2011/04/ubuntu-server-initial-security-quick-secure-setup-part-i/ - Ubuntu Server Initial Security guide
• https://www.tldp.org/LDP/sag/html/index.html
• https://seifried.org/lasg/
• https://news.ycombinator.com/item?id=19178964
• https://wiki.archlinux.org/index.php/Security - many folks have also recommended this one
• https://securecompliance.co/linux-server-hardening-checklist/

(Table of Contents)

To Do / To Add

• Custom Jails for Fail2ban
• MAC (Mandatory Access Control) and Linux Security Modules (LSMs)
  • https://wiki.archlinux.org/index.php/security#Mandatory_access_control
  • Security-Enhanced Linux / SELinux
    • https://en.wikipedia.org/wiki/Security-Enhanced_Linux
    • https://linuxtechlab.com/beginners-guide-to-selinux/
    • https://linuxtechlab.com/replicate-selinux-policies-among-linux-machines/
    • https://teamignition.us/how-to-stop-being-a-scrub-and-learn-to-use-selinux.html
  • AppArmor
    • https://wiki.archlinux.org/index.php/AppArmor
    • https://security.stackexchange.com/questions/29378/comparison-between-apparmor-and-selinux
    • http://www.insanitybit.com/2012/06/01/why-i-like-apparmor-more-than-selinux-5/
• disk encryption
• Rkhunter and chrootkit
  • http://www.chkrootkit.org/
  • http://rkhunter.sourceforge.net/
  • https://www.cyberciti.biz/faq/howto-check-linux-rootkist-with-detectors-software/
  • https://www.tecmint.com/install-rootkit-hunter-scan-for-rootkits-backdoors-in-linux/
• shipping/backing up logs - https://news.ycombinator.com/item?id=19178681
• CIS-CAT - https://learn.cisecurity.org/cis-cat-landing-page
• debsums - https://blog.sleeplessbeastie.eu/2015/03/02/how-to-verify-installed-packages/

Guide Overview

About This Guide

This guide...

• ...is a work in progress.
• ...is focused on at-home Linux servers. All of the concepts/recommendations here apply to larger/professional environments but those use-cases call for more advanced and specialized configurations that are out-of-scope for this guide.
• ...does not teach you about Linux, how to install Linux, or how to use it. Check https://linuxjourney.com/ if you're new to Linux.
• ...is meant to be Linux distribution agnostic.
• ...does not teach you everything you need to know about security nor does it get into all aspects of system/server security. For example, physical security is out of scope for this guide.
• ...does not talk about how programs/tools work, nor does it delve into their nook and crannies. Most of the programs/tools this guide references are very powerful and highly configurable. The goal is to cover the bare necessities -- enough to whet your appetite and make you hungry enough to want to go and learn more.
• ...aims to make it easy by providing code you can copy-and-paste. You might need to modify the commands before you paste so keep your favorite text editor handy.
• ...is organized in an order that makes logical sense to me -- i.e. securing SSH before installing a firewall. As such, this guide is intended to be followed in the order it is presented but it is not necessary to do so. Just be careful if you do things in a different order -- some sections require previous sections to be completed.

My Use-Case

There are many types of servers and different use-cases. While I want this guide to be as generic as possible, there will be some things that may not apply to all/other use-cases. Use your best judgement when going through this guide.

To help put context to many of the topics covered in this guide, my use-case/configuration is:

• A desktop class computer...
• With a single NIC...
• Connected to a consumer grade router...
• Getting a dynamic WAN IP provided by the ISP...
• With WAN+LAN on IPV4...
• And LAN using NAT...
• That I want to be able to SSH to remotely from unknown computers and unknown locations (i.e. a friend's house).

Editing Configuration Files - For The Lazy

I am very lazy and do not like to edit files by hand if I don't need to. I also assume everyone else is just like me. :)

So, when and where possible, I have provided code snippets to quickly do what is needed, like add or change a line in a configuration file.

The code snippets use basic commands like echo, cat, sed, awk, and grep. How the code snippets work, like what each command/part does, is out of scope for this guide -- the man pages are your friend.

Note: The code snippets do not validate/verify the change went through -- i.e. the line was actually added or changed. I'll leave the verifying part in your capable hands. The steps in this guide do include taking backups of all files that will be changed.

Not all changes can be automated with code snippets. Those changes need good, old fashioned, manual editing. For example, you can't just append a line to an INI type file. Use your favorite Linux text editor.

Contributing

I wanted to put this guide on GitHub to make it easy to collaborate. The more folks that contribute, the better and more complete this guide will become.

To contribute you can fork and submit a pull request or submit a new issue.

Before You Start

Identify Your Principles

Before you start you will want to identify what your Principles are. What is your threat model? Some things to think about:

• Why do you want to secure your server?
• How much security do you want or not want?
• How much convenience are you willing to compromise for security and vice-versa?
• What are the threats you want to protect against? What are the specifics to your situation? For example:
  • Is physical access to your server/network a possible attack vector?
  • Will you be opening ports on your router so you can access your server from outside your home?
  • Will you be hosting a file share on your server that will be mounted on a desktop class machine? What is the possibility of the desktop machine getting infected and, in turn, infecting the server?
• Do you have a means of recovering if your security implementation locks you out of your own server? For example, you disabled root login or password protected GRUB.

These are just a few things to think about. Before you start securing your server you will want to understand what you're trying to protect against and why so you know what you need to do.

Picking A Linux Distribution

This guide is intended to be distribution agnostic so users can use any distribution they want. With that said, there are a few things to keep in mind:

You want a distribution that...

• ...is stable. Unless you like debugging issues at 2 AM, you don't want an unattended upgrade, or a manual package/system update, to render your server inoperable. But this also means you're okay with not running the latest, greatest, bleeding edge software.
• ...stays up-to-date with security patches. You can secure everything on your server, but if the core OS or applications you're running have known vulnerabilities, you'll never be safe.
• ...you're familiar with. If you don't know Linux, I would advise you play around with one before you try to secure it. You should be comfortable with it and know your way around, like how to install software, where configuration files are, etc...
• ...is well supported. Even the most seasoned admin needs help every now and then. Having a place to go for help will save your sanity.

Installing Linux

Installing Linux is out-of-scope for this guide because each distribution does it differently and the installation instructions are usually well documented. If you need help, start with your distribution's documentation. Regardless of the distribution, the high-level process usually goes like so:

1. download the ISO
2. burn/copy/transfer it to your install medium (e.g. a CD or USB stick)
3. boot your server from your install medium
4. follow the prompts to install

Where applicable, use the expert install option so you have tighter control of what is running on your server. Only install what you absolutely need. I, personally, do not install anything other than SSH. Also, tick the Disk Encryption option.

Pre/Post Installation Requirements

• If you're opening ports on your router so you can access your server from the outside, disable the port forwarding until your system is up and secured.
• Unless you're doing everything physically connected to your server, you'll need remote access so be sure SSH works.
• Keep your system up-to-date (i.e. sudo apt update && sudo apt upgrade on Debian based systems).
• Make sure you perform any tasks specific to your setup like:
  • Configuring network
  • Configuring mount points in /etc/fstab
  • Creating the initial user accounts
  • Installing core software you'll want like man
  • Etc...
• Your server will need to be able to send e-mails so you can get important security alerts. If you're not setting up a mail server check Gmail and Exim4 As MTA With Implicit TLS.
• I would also recommend you go through the CIS Benchmarks before you start with this guide.

Other Important Notes

• This guide is being written and tested on Debian. Most things below should work on other distributions. If you find something that does not, please contact me. The main thing that separates each distribution will be its package management system. Since I use Debian, I will provide the appropriate apt commands that should work on all Debian based distributions. If someone is willing to provide the respective commands for other distributions, I will add them.
• File paths and settings also may differ slightly -- check with your distribution's documentation if you have issues.
• Read the whole guide before you start. Your use-case and/or principals may call for not doing something or for changing the order.
• Do not blindly copy-and-paste without understanding what you're pasting. Some commands will need to be modified for your needs before they'll work -- usernames for example.

The SSH Server

Important Note Before You Make SSH Changes

It is highly advised you keep a 2nd terminal open to your server before you make and apply SSH configuration changes. This way if you lock yourself out of your 1st terminal session, you still have one session connected so you can fix it.

Thank you to Sonnenbrand for this idea.

SSH Public/Private Keys

Why

Using SSH public/private keys is more secure than using a password. It also makes it easier and faster, to connect to our server because you don't have to enter a password.

How It Works

Check the references below for more details but, at a high level, public/private keys work by using a pair of keys to verify identity.

1. One key, the public key, can only encrypt data, not decrypt it
2. The other key, the private key, can decrypt the data

For SSH, a public and private key is created on the client. You want to keep both keys secure, especially the private key. Even though the public key is meant to be public, it is wise to make sure neither keys fall in the wrong hands.

When you connect to an SSH server, SSH will look for a public key that matches the client you're connecting from in the file ~/.ssh/authorized_keys on the server you're connecting to. Notice the file is in the home folder of the ID you're trying to connect to. So, after creating the public key, you need to append it to ~/.ssh/authorized_keys. One approach is to copy it to a USB stick and physically transfer it to the server. Another approach is to use use ssh-copy-id to transfer and append the public key.

After the keys have been created and the public key has been appended to ~/.ssh/authorized_keys on the host, SSH uses the public and private keys to verify identity and then establish a secure connection. How identity is verified is a complicated process but Digital Ocean has a very nice write-up of how it works. At a high level, identity is verified by the server encrypting a challenge message with the public key, then sending it to the client. If the client cannot decrypt the challenge message with the private key, the identity can't be verified and a connection will not be established.

They are considered more secure because you need the private key to establish an SSH connection. If you set PasswordAuthentication no in /etc/ssh/sshd_config, then SSH won't let you connect without the private key.

You can also set a pass-phrase for the keys which would require you to enter the key pass-phrase when connecting using public/private keys. Keep in mind doing this means you can't use the key for automation because you'll have no way to send the passphrase in your scripts. ssh-agent is a program that is shipped in many Linux distros (and usually already running) that will allow you to hold your unencrypted private key in memory for a configurable duration. Simply run ssh-add and it will prompt you for your passphrase. You will not be prompted for your passphrase again until the configurable duration has passed.

We will be using Ed25519 keys which, according to https://linux-audit.com/:

It is using an elliptic curve signature scheme, which offers better security than ECDSA and DSA. At the same time, it also has good performance.

Goals

• Ed25519 public/private SSH keys:
  • private key on your client
  • public key on your server

Notes

• You'll need to do this step for every computer and account you'll be connecting to your server from/as.

References

• https://www.ssh.com/ssh/public-key-authentication
• https://help.ubuntu.com/community/SSH/OpenSSH/Keys
• https://linux-audit.com/using-ed25519-openssh-keys-instead-of-dsa-rsa-ecdsa/
• https://www.digitalocean.com/community/tutorials/understanding-the-ssh-encryption-and-connection-process
• https://wiki.archlinux.org/index.php/SSH_Keys
• https://www.ssh.com/ssh/copy-id
• man ssh-keygen
• man ssh-copy-id
• man ssh-add

Steps

From the computer you're going to use to connect to your server, the client, not the server itself, create an Ed25519 key with ssh-keygen:

ssh-keygen -t ed25519

Generating public/private ed25519 key pair.
Enter file in which to save the key (/home/user/.ssh/id_ed25519):
Created directory '/home/user/.ssh'.
Enter passphrase (empty for no passphrase):
Enter same passphrase again:
Your identification has been saved in /home/user/.ssh/id_ed25519.
Your public key has been saved in /home/user/.ssh/id_ed25519.pub.
The key fingerprint is:
SHA256:F44D4dr2zoHqgj0i2iVIHQ32uk/Lx4P+raayEAQjlcs user@client
The key's randomart image is:
+--[ED25519 256]--+
|xxxx  x          |
|o.o +. .         |
| o o oo   .      |
|. E oo . o .     |
| o o. o S o      |
|... .. o o       |
|.+....+ o        |
|+.=++o.B..       |
|+..=**=o=.       |
+----[SHA256]-----+

Note: If you set a passphrase, you'll need to enter it every time you connect to your server using this key, unless you're using ssh-agent.

Now you need to append the public key ~/.ssh/id_ed25519.pub from your client to the ~/.ssh/authorized_keys file on your server. Since we're presumable still at home on the LAN, we're probably safe from MIM attacks, so we will use ssh-copy-id to transfer and append the public key:

ssh-copy-id user@server

/usr/bin/ssh-copy-id: INFO: Source of key(s) to be installed: "/home/user/.ssh/id_ed25519.pub"
The authenticity of host 'host (192.168.1.96)' can't be established.
ECDSA key fingerprint is SHA256:QaDQb/X0XyVlogh87sDXE7MR8YIK7ko4wS5hXjRySJE.
Are you sure you want to continue connecting (yes/no)? yes
/usr/bin/ssh-copy-id: INFO: attempting to log in with the new key(s), to filter out any that are already installed
/usr/bin/ssh-copy-id: INFO: 1 key(s) remain to be installed -- if you are prompted now it is to install the new keys
user@host's password:

Number of key(s) added: 1

Now try logging into the machine, with:   "ssh 'user@host'"
and check to make sure that only the key(s) you wanted were added.

Now would be a good time to perform any tasks specific to your setup.

Create SSH Group For AllowGroups

Why

To make it easy to control who can SSH to the server. By using a group, we can quickly add/remove accounts to the group to quickly allow or not allow SSH access to the server.

How It Works

We will use the AllowGroups option in SSH's configuration file /etc/ssh/sshd_config to tell the SSH server to only allow users to SSH in if they are a member of a certain UNIX group. Anyone not in the group will not be able to SSH in.

Goals

• a UNIX group that we'll use in Secure /etc/ssh/sshd_config to limit who can SSH to the server

Notes

• This is a per-requisite step to support the AllowGroup setting set in Secure /etc/ssh/sshd_config.

References

• man groupadd
• man usermod

Steps

Create a group:

sudo groupadd sshusers

Add account(s) to the group:

sudo usermod -a -G sshusers user1
sudo usermod -a -G sshusers user2
sudo usermod -a -G sshusers ...

You'll need to do this for every account on your server that needs SSH access.

Secure /etc/ssh/sshd_config

Why

SSH is a door into your server. This is especially true if you are opening ports on your router so you can SSH to your server from outside your home network. If it is not secured properly, a bad-actor could use it to gain unauthorized access to your system.

How It Works

/etc/ssh/sshd_config is the default configuration file that the SSH server uses. We will use this file to tell what options the SSH server should use.

Goals

• a secure SSH configuration

Notes

• Make sure you've completed Create SSH Group For AllowGroups first.

References

• Mozilla's OpenSSH guidelines for OpenSSH 6.7+ at https://infosec.mozilla.org/guidelines/openssh#modern-openssh-67
• https://linux-audit.com/audit-and-harden-your-ssh-configuration/
• https://www.ssh.com/ssh/sshd_config/
• https://www.techbrown.com/harden-ssh-secure-linux-vps-server/
• https://serverfault.com/questions/660160/openssh-difference-between-internal-sftp-and-sftp-server/660325
• man sshd_config
• Thanks to than0s for how to find duplicate settings.

Steps

Make a backup of OpenSSH server's configuration file /etc/ssh/sshd_config and remove comments to make it easier to read:

sudo cp --archive /etc/ssh/sshd_config /etc/ssh/sshd_config-COPY-$(date +"%Y%m%d%H%M%S")
sudo sed -i -r -e '/^#|^$/ d' /etc/ssh/sshd_config

Edit /etc/ssh/sshd_config then find and edit or add these settings that should be applied regardless of your configuration/setup:

Note: SSH does not like duplicate contradicting settings. For example, if you have ChallengeResponseAuthentication no and then ChallengeResponseAuthentication yes, SSH will respect the first one and ignore the second. Your /etc/ssh/sshd_config file may already have some of the settings/lines below. To avoid issues you will need to manually go through your /etc/ssh/sshd_config file and address any duplicate contradicting settings.

########################################################################################################
# start settings from https://infosec.mozilla.org/guidelines/openssh#modern-openssh-67 as of 2019-01-01
########################################################################################################

# Supported HostKey algorithms by order of preference.
HostKey /etc/ssh/ssh_host_ed25519_key
HostKey /etc/ssh/ssh_host_rsa_key
HostKey /etc/ssh/ssh_host_ecdsa_key

KexAlgorithms curve25519-sha256@libssh.org,ecdh-sha2-nistp521,ecdh-sha2-nistp384,ecdh-sha2-nistp256,diffie-hellman-group-exchange-sha256

Ciphers chacha20-poly1305@openssh.com,aes256-gcm@openssh.com,aes128-gcm@openssh.com,aes256-ctr,aes192-ctr,aes128-ctr

MACs hmac-sha2-512-etm@openssh.com,hmac-sha2-256-etm@openssh.com,hmac-sha2-512,hmac-sha2-256,umac-128@openssh.com

# LogLevel VERBOSE logs user's key fingerprint on login. Needed to have a clear audit track of which key was using to log in.
LogLevel VERBOSE

# Use kernel sandbox mechanisms where possible in unprivileged processes
# Systrace on OpenBSD, Seccomp on Linux, seatbelt on MacOSX/Darwin, rlimit elsewhere.
# Note: This setting is deprecated in OpenSSH 7.5 (https://www.openssh.com/txt/release-7.5)
# UsePrivilegeSeparation sandbox

########################################################################################################
# end settings from https://infosec.mozilla.org/guidelines/openssh#modern-openssh-67 as of 2019-01-01
########################################################################################################

# don't let users set environment variables
PermitUserEnvironment no

# Log sftp level file access (read/write/etc.) that would not be easily logged otherwise.
Subsystem sftp  internal-sftp -f AUTHPRIV -l INFO

# only use the newer, more secure protocol
Protocol 2

# disable X11 forwarding as X11 is very insecure
# you really shouldn't be running X on a server anyway
X11Forwarding no

# disable port forwarding
AllowTcpForwarding no
AllowStreamLocalForwarding no
GatewayPorts no
PermitTunnel no

# don't allow login if the account has an empty password
PermitEmptyPasswords no

# ignore .rhosts and .shosts
IgnoreRhosts yes

# verify hostname matches IP
UseDNS yes

Compression no
TCPKeepAlive no
AllowAgentForwarding no
PermitRootLogin no

# don't allow .rhosts or /etc/hosts.equiv
HostbasedAuthentication no

Then find and edit or add these settings, and set values as per your requirements:

Setting	Valid Values	Example	Description	Notes
AllowGroups	local UNIX group name	AllowGroups sshusers	group to allow SSH access to
ClientAliveCountMax	number	ClientAliveCountMax 0	maximum number of client alive messages sent without response
ClientAliveInterval	number of seconds	ClientAliveInterval 300	timeout in seconds before a response request
ListenAddress	space separated list of local addresses	ListenAddress 0.0.0.0 ListenAddress 192.168.1.100	local addresses sshd should listen on	See Issue #1 for important details.
LoginGraceTime	number of seconds	LoginGraceTime 30	time in seconds before login times-out
MaxAuthTries	number	MaxAuthTries 2	maximum allowed attempts to login
MaxSessions	number	MaxSessions 2	maximum number of open sessions
MaxStartups	number	MaxStartups 2	maximum number of login sessions
PasswordAuthentication	yes or no	PasswordAuthentication no	if login with a password is allowed
Port	any open/available port number	Port 22	port that sshd should listen on

Check man sshd_config for more details what these settings mean.

Make sure there are no duplicate settings that contradict each other. The below command should not have any output.

awk 'NF && $1!~/^(#|HostKey)/{print $1}' /etc/ssh/sshd_config | sort | uniq -c | grep -v ' 1 '

Restart ssh:

sudo service sshd restart

You can check verify the configurations worked with sshd -T and verify the output:

sudo sshd -T

port 22
addressfamily any
listenaddress [::]:22
listenaddress 0.0.0.0:22
usepam yes
logingracetime 30
x11displayoffset 10
maxauthtries 2
maxsessions 2
clientaliveinterval 300
clientalivecountmax 0
streamlocalbindmask 0177
permitrootlogin no
ignorerhosts yes
ignoreuserknownhosts no
hostbasedauthentication no
...
subsystem sftp internal-sftp -f AUTHPRIV -l INFO
maxstartups 2:30:2
permittunnel no
ipqos lowdelay throughput
rekeylimit 0 0
permitopen any

Remove Short Diffie-Hellman Keys

Why

Per Mozilla's OpenSSH guidelines for OpenSSH 6.7+, "all Diffie-Hellman moduli in use should be at least 3072-bit-long".

The Diffie-Hellman algorithm is used by SSH to establish a secure connection. The larger the moduli (key size) the stronger the encryption.

Goals

• remove all Diffie-Hellman keys that are less than 3072 bits long

References

• Mozilla's OpenSSH guidelines for OpenSSH 6.7+ at https://infosec.mozilla.org/guidelines/openssh#modern-openssh-67
• https://infosec.mozilla.org/guidelines/key_management
• man moduli

Steps

Make a backup of SSH's moduli file /etc/ssh/moduli:

sudo cp --archive /etc/ssh/moduli /etc/ssh/moduli-COPY-$(date +"%Y%m%d%H%M%S")

Remove short moduli:

sudo awk '$5 >= 3071' /etc/ssh/moduli | sudo tee /etc/ssh/moduli.tmp
sudo mv /etc/ssh/moduli.tmp /etc/ssh/moduli

2FA/MFA for SSH

Why

Even though SSH is a pretty good security guard for your doors and windows, it is still a visible door that bad-actors can see and try to brute-force in. Fail2ban will monitor for these brute-force attempts but there is no such thing as being too secure. Requiring two factors adds an extra layer of security.

Using Two Factor Authentication (2FA) / Multi Factor Authentication (MFA) requires anyone entering to have two keys to enter which makes it harder for bad actors. The two keys are:

1. Their password
2. A 6 digit token that changes every 30 seconds

Without both keys, they won't be able to get in.

Why Not

Many folks might find the experience cumbersome or annoying. And, access to your system is dependent on the accompanying authenticator app that generates the code.

How It Works

On Linux, PAM is responsible for authentication. There are four tasks to PAM that you can read about at https://en.wikipedia.org/wiki/Linux_PAM. This section talks about the authentication task.

When you log into a server, be it directly from the console or via SSH, the door you came through will send the request to the authentication task of PAM and PAM will ask for and verify your password. You can customize the rules each doors use. For example, you could have one set of rules when logging in directly from the console and another set of rules for when logging in via SSH.

This section will alter the authentication rules for when logging in via SSH to require both a password and a 6 digit code.

We will use Google's libpam-google-authenticator PAM module to create and verify a TOTP key. https://fastmail.blog/2016/07/22/how-totp-authenticator-apps-work/ and https://jemurai.com/2018/10/11/how-it-works-totp-based-mfa/ have very good writeups of how TOTP works.

What we will do is tell the server's SSH PAM configuration to ask the user for their password and then their numeric token. PAM will then verify the user's password and, if it is correct, then it will route the authentication request to libpam-google-authenticator which will ask for and verify your 6 digit token. If, and only if, everything is good will the authentication succeed and user be allowed to log in.

Goals

• 2FA/MFA enabled for all SSH connections

Notes

• Before you do this, you should have an idea of how 2FA/MFA works and you'll need an authenticator app on your phone to continue.
• We'll use google-authenticator-libpam.
• With the below configuration, a user will only need to enter their 2FA/MFA code if they are logging on with their password but not if they are using SSH public/private keys. Check the documentation on how to change this behavior to suite your requirements.

References

• https://github.com/google/google-authenticator-libpam
• https://en.wikipedia.org/wiki/Linux_PAM
• https://en.wikipedia.org/wiki/Time-based_One-time_Password_algorithm
• https://fastmail.blog/2016/07/22/how-totp-authenticator-apps-work/
• https://jemurai.com/2018/10/11/how-it-works-totp-based-mfa/

Steps

Install it libpam-google-authenticator.

On Debian based systems:

sudo apt install libpam-google-authenticator

Make sure you're logged in as the ID you want to enable 2FA/MFA for and execute google-authenticator to create the necessary token data:

google-authenticator

Do you want authentication tokens to be time-based (y/n) y
https://www.google.com/chart?chs=200x200&chld=M|0&cht=qr&chl=otpauth://totp/user@host%3Fsecret%3DR4ZWX34FQKZROVX7AGLJ64684Y%26issuer%3Dhost

...

Your new secret key is: R3NVX3FFQKZROVX7AGLJUGGESY
Your verification code is 751419
Your emergency scratch codes are:
  12345678
  90123456
  78901234
  56789012
  34567890

Do you want me to update your "/home/user/.google_authenticator" file (y/n) y

Do you want to disallow multiple uses of the same authentication
token? This restricts you to one login about every 30s, but it increases
your chances to notice or even prevent man-in-the-middle attacks (y/n) Do you want to disallow multiple uses of the same authentication
token? This restricts you to one login about every 30s, but it increases
your chances to notice or even prevent man-in-the-middle attacks (y/n) y

By default, tokens are good for 30 seconds. In order to compensate for
possible time-skew between the client and the server, we allow an extra
token before and after the current time. If you experience problems with
poor time synchronization, you can increase the window from its default
size of +-1min (window size of 3) to about +-4min (window size of
17 acceptable tokens).
Do you want to do so? (y/n) y

If the computer that you are logging into isn't hardened against brute-force
login attempts, you can enable rate-limiting for the authentication module.
By default, this limits attackers to no more than 3 login attempts every 30s.
Do you want to enable rate-limiting (y/n) y

Notice this is not run as root.

Select default option (y in most cases) for all the questions it asks and remember to save the emergency scratch codes.

Make a backup of PAM's SSH configuration file /etc/pam.d/sshd:

sudo cp --archive /etc/pam.d/sshd /etc/pam.d/sshd-COPY-$(date +"%Y%m%d%H%M%S")

Now we need to enable it as an authentication method for SSH by adding this line to /etc/pam.d/sshd:

auth       required     pam_google_authenticator.so nullok

Note: Check here for what nullok means.

For the lazy:

echo -e "\nauth       required     pam_google_authenticator.so nullok         # added by $(whoami) on $(date +"%Y-%m-%d @ %H:%M:%S")" | sudo tee -a /etc/pam.d/sshd

Tell SSH to leverage it by adding or editing this line in /etc/ssh/sshd_config:

ChallengeResponseAuthentication yes

For the lazy:

sudo sed -i -r -e "s/^(challengeresponseauthentication .*)$/# \1         # commented by $(whoami) on $(date +"%Y-%m-%d @ %H:%M:%S")/I" /etc/ssh/sshd_config
echo -e "\nChallengeResponseAuthentication yes         # added by $(whoami) on $(date +"%Y-%m-%d @ %H:%M:%S")" | sudo tee -a /etc/ssh/sshd_config

Restart ssh:

sudo service sshd restart

The Basics

Limit Who Can Use sudo

Why

sudo lets accounts run commands as other accounts, including root. We want to make sure that only the accounts we want can use sudo.

Goals

• sudo privileges limited to those who are in a group we specify

Notes

• Your installation may have already done this, or may already have a special group intended for this purpose so check first.
  • Debian creates the sudo group
  • RedHat creates the wheel group
• See https://github.com/imthenachoman/How-To-Secure-A-Linux-Server/issues/39 for a note on some distributions making it so sudo does not require a password. Thanks to sbrl for sharing.

Steps

Create a group:

sudo groupadd sudousers

Add account(s) to the group:

sudo usermod -a -G sudousers user1
sudo usermod -a -G sudousers user2
sudo usermod -a -G sudousers  ...

You'll need to do this for every account on your server that needs sudo privileges.

Make a backup of the sudo's configuration file /etc/sudoers:

sudo cp --archive /etc/sudoers /etc/sudoers-COPY-$(date +"%Y%m%d%H%M%S")

Edit sudo's configuration file /etc/sudoers:

sudo visudo

Tell sudo to only allow users in the sudousers group to use sudo by adding this line if it is not already there:

%sudousers   ALL=(ALL:ALL) ALL

Limit Who Can Use su

Why

su also lets accounts run commands as other accounts, including root. We want to make sure that only the accounts we want can use su.

Goals

• su privileges limited to those who are in a group we specify

References

• Thanks to olavim for sharing this idea

Steps

Create a group:

sudo groupadd suusers

Add account(s) to the group:

sudo usermod -a -G suusers user1
sudo usermod -a -G suusers user2
sudo usermod -a -G suusers  ...

You'll need to do this for every account on your server that needs sudo privileges.

Make it so only users in this group can execute /bin/su:

sudo dpkg-statoverride --update --add root suusers 4750 /bin/su

Run applications in a sandbox with FireJail

Why

It's absolutely better, for many applications, to run in a sandbox.

Browsers (even more the Closed Source ones) and eMail Clients are highly suggested.

Goals

• confine applications in a jail (few safe directories) and block access to the rest of the system

References

• Thanks to FireJail

Steps

Install the software:

sudo apt install firejail firejail-profiles

Note: for Debian 10 Stable, official Backport is suggested:

sudo apt install -t buster-backports firejail firejail-profiles

Allow an application (installed in /usr/bin or /bin) to run only in a sandbox (see few examples below here):

sudo ln -s /usr/bin/firejail /usr/local/bin/google-chrome-stable
sudo ln -s /usr/bin/firejail /usr/local/bin/firefox
sudo ln -s /usr/bin/firejail /usr/local/bin/chromium
sudo ln -s /usr/bin/firejail /usr/local/bin/evolution
sudo ln -s /usr/bin/firejail /usr/local/bin/thunderbird

Run the application as usual (via terminal or launcher) and check if is running in a jail:

firejail --list

Allow a sandboxed app to run again as it was before (example: firefox)

sudo rm /usr/local/bin/firefox

NTP Client

Why

Many security protocols leverage the time. If your system time is incorrect, it could have negative impacts to your server. An NTP client can solve that problem by keeping your system time in-sync with global NTP servers

How It Works

NTP stands for Network Time Protocol. In the context of this guide, an NTP client on the server is used to update the server time with the official time pulled from official servers. Check https://www.pool.ntp.org/en/ for all of the public NTP servers.

Goals

• NTP client installed and keeping server time in-sync

References

• https://cloudpro.zone/index.php/2018/01/27/debian-9-3-server-setup-guide-part-4/
• https://en.wikipedia.org/wiki/Network_Time_Protocol
• https://www.pool.ntp.org/en/
• https://serverfault.com/questions/957302/securing-hardening-ntp-client-on-linux-servers-config-file/957450#957450
• https://tf.nist.gov/tf-cgi/servers.cgi

Steps

Install ntp.

On Debian based systems:

sudo apt install ntp

Make a backup of the NTP client's configuration file /etc/ntp.conf:

sudo cp --archive /etc/ntp.conf /etc/ntp.conf-COPY-$(date +"%Y%m%d%H%M%S")

The default configuration, at least on Debian, is already pretty secure. The only thing we'll want to make sure is we're the pool directive and not any server directives. The pool directive allows the NTP client to stop using a server if it is unresponsive or serving bad time. Do this by commenting out all server directives and adding the below to /etc/ntp.conf.

pool pool.ntp.org iburst

For the lazy:

sudo sed -i -r -e "s/^((server|pool).*)/# \1         # commented by $(whoami) on $(date +"%Y-%m-%d @ %H:%M:%S")/" /etc/ntp.conf
echo -e "\npool pool.ntp.org iburst         # added by $(whoami) on $(date +"%Y-%m-%d @ %H:%M:%S")" | sudo tee -a /etc/ntp.conf

Example /etc/ntp.conf:

driftfile /var/lib/ntp/ntp.drift
statistics loopstats peerstats clockstats
filegen loopstats file loopstats type day enable
filegen peerstats file peerstats type day enable
filegen clockstats file clockstats type day enable
restrict -4 default kod notrap nomodify nopeer noquery limited
restrict -6 default kod notrap nomodify nopeer noquery limited
restrict 127.0.0.1
restrict ::1
restrict source notrap nomodify noquery
pool pool.ntp.org iburst         # added by user on 2019-03-09 @ 10:23:35

Restart ntp:

sudo service ntp restart

Check the status of the ntp service:

sudo systemctl status ntp

● ntp.service - LSB: Start NTP daemon
   Loaded: loaded (/etc/init.d/ntp; generated; vendor preset: enabled)
   Active: active (running) since Sat 2019-03-09 15:19:46 EST; 4s ago
     Docs: man:systemd-sysv-generator(8)
  Process: 1016 ExecStop=/etc/init.d/ntp stop (code=exited, status=0/SUCCESS)
  Process: 1028 ExecStart=/etc/init.d/ntp start (code=exited, status=0/SUCCESS)
    Tasks: 2 (limit: 4915)
   CGroup: /system.slice/ntp.service
           └─1038 /usr/sbin/ntpd -p /var/run/ntpd.pid -g -u 108:113

Mar 09 15:19:46 host ntpd[1038]: Listen and drop on 0 v6wildcard [::]:123
Mar 09 15:19:46 host ntpd[1038]: Listen and drop on 1 v4wildcard 0.0.0.0:123
Mar 09 15:19:46 host ntpd[1038]: Listen normally on 2 lo 127.0.0.1:123
Mar 09 15:19:46 host ntpd[1038]: Listen normally on 3 enp0s3 10.10.20.96:123
Mar 09 15:19:46 host ntpd[1038]: Listen normally on 4 lo [::1]:123
Mar 09 15:19:46 host ntpd[1038]: Listen normally on 5 enp0s3 [fe80::a00:27ff:feb6:ed8e%2]:123
Mar 09 15:19:46 host ntpd[1038]: Listening on routing socket on fd #22 for interface updates
Mar 09 15:19:47 host ntpd[1038]: Soliciting pool server 108.61.56.35
Mar 09 15:19:48 host ntpd[1038]: Soliciting pool server 69.89.207.199
Mar 09 15:19:49 host ntpd[1038]: Soliciting pool server 45.79.111.114

Check ntp's status:

sudo ntpq -p

     remote           refid      st t when poll reach   delay   offset  jitter
==============================================================================
 pool.ntp.org    .POOL.          16 p    -   64    0    0.000    0.000   0.000
*lithium.constan 198.30.92.2      2 u    -   64    1   19.900    4.894   3.951
 ntp2.wiktel.com 212.215.1.157    2 u    2   64    1   48.061   -0.431   0.104

Securing /proc

Why

To quote https://linux-audit.com/linux-system-hardening-adding-hidepid-to-proc/:

When looking in /proc you will discover a lot of files and directories. Many of them are just numbers, which represent the information about a particular process ID (PID). By default, Linux systems are deployed to allow all local users to see this all information. This includes process information from other users. This could include sensitive details that you may not want to share with other users. By applying some filesystem configuration tweaks, we can change this behavior and improve the security of the system.

Note: This may break on some systemd systems. Please see https://github.com/imthenachoman/How-To-Secure-A-Linux-Server/issues/37 for more information. Thanks to nlgranger for sharing.

Goals

• /proc mounted with hidepid=2 so users can only see information about their processes

References

• https://linux-audit.com/linux-system-hardening-adding-hidepid-to-proc/
• https://likegeeks.com/secure-linux-server-hardening-best-practices/#Hardening-proc-Directory
• https://www.cyberciti.biz/faq/linux-hide-processes-from-other-users/

Steps

Make a backup of /etc/fstab:

sudo cp --archive /etc/fstab /etc/fstab-COPY-$(date +"%Y%m%d%H%M%S")

Add this line to /etc/fstab to have /proc mounted with hidepid=2:

proc     /proc     proc     defaults,hidepid=2     0     0

For the lazy:

echo -e "\nproc     /proc     proc     defaults,hidepid=2     0     0         # added by $(whoami) on $(date +"%Y-%m-%d @ %H:%M:%S")" | sudo tee -a /etc/fstab

Reboot the system:

sudo reboot now

Note: Alternatively, you can remount /proc without rebooting with sudo mount -o remount,hidepid=2 /proc

Force Accounts To Use Secure Passwords

Why

By default, accounts can use any password they want, including bad ones. pwquality/pam_pwquality addresses this security gap by providing "a way to configure the default password quality requirements for the system passwords" and checking "its strength against a system dictionary and a set of rules for identifying poor choices."

How It Works

On Linux, PAM is responsible for authentication. There are four tasks to PAM that you can read about at https://en.wikipedia.org/wiki/Linux_PAM. This section talks about the password task.

When there is a need to set or change an account password, the password task of PAM handles the request. In this section we will tell PAM's password task to pass the requested new password to libpam-pwquality to make sure it meets our requirements. If the requirements are met it is used/set; if it does not meet the requirements it errors and lets the user know.

Goals

• enforced strong passwords

Steps

Install libpam-pwquality.

On Debian based systems:

sudo apt install libpam-pwquality

Make a backup of PAM's password configuration file /etc/pam.d/common-password:

sudo cp --archive /etc/pam.d/common-password /etc/pam.d/common-password-COPY-$(date +"%Y%m%d%H%M%S")

Tell PAM to use libpam-pwquality to enforce strong passwords by editing the file /etc/pam.d/common-password and change the line that starts like this:

password        requisite                       pam_pwquality.so

to this:

password        requisite                       pam_pwquality.so retry=3 minlen=10 difok=3 ucredit=-1 lcredit=-1 dcredit=-1 ocredit=-1 maxrepeat=3 gecoschec

The above options are:

• retry=3 = prompt user 3 times before returning with error.
• minlen=10 = the minimum length of the password, factoring in any credits (or debits) from these:
  • dcredit=-1 = must have at least one digit
  • ucredit=-1 = must have at least one upper case letter
  • lcredit=-1 = must have at least one lower case letter
  • ocredit=-1 = must have at least one non-alphanumeric character
• difok=3 = at least 3 characters from the new password cannot have been in the old password
• maxrepeat=3 = allow a maximum of 3 repeated characters
• gecoschec = do not allow passwords with the account's name

sudo sed -i -r -e "s/^(password\s+requisite\s+pam_pwquality.so)(.*)$/# \1\2         # commented by $(whoami) on $(date +"%Y-%m-%d @ %H:%M:%S")\n\1 retry=3 minlen=10 difok=3 ucredit=-1 lcredit=-1 dcredit=-1 ocredit=-1 maxrepeat=3 gecoschec         # added by $(whoami) on $(date +"%Y-%m-%d @ %H:%M:%S")/" /etc/pam.d/common-password

Automatic Security Updates and Alerts

Why

It is important to keep a server updated with the latest critical security patches and updates. Otherwise you're at risk of known security vulnerabilities that bad-actors could use to gain unauthorized access to your server.

Unless you plan on checking your server every day, you'll want a way to automatically update the system and/or get emails about available updates.

You don't want to do all updates because with every update there is a risk of something breaking. It is important to do the critical updates but everything else can wait until you have time to do it manually.

Why Not

Automatic and unattended updates may break your system and you may not be near your server to fix it. This would be especially problematic if it broke your SSH access.

Notes

• Each distribution manages packages and updates differently. So far I only have steps for Debian based systems.
• Your server will need a way to send e-mails for this to work

Goals

• Automatic, unattended, updates of critical security patches
• Automatic emails of remaining pending updates

Debian Based Systems

How It Works

On Debian based systems you can use:

• unattended-upgrades to automatically do system updates you want (i.e. critical security updates)
• apt-listchanges to get details about package changes before they are installed/upgraded
• apticron to get emails for pending package updates

We will use unattended-upgrades to apply critical security patches. We can also apply stable updates since they've already been thoroughly tested by the Debian community.

References

• https://wiki.debian.org/UnattendedUpgrades
• https://debian-handbook.info/browse/stable/sect.regular-upgrades.html
• https://blog.sleeplessbeastie.eu/2015/01/02/how-to-perform-unattended-upgrades/
• https://www.vultr.com/docs/how-to-set-up-unattended-upgrades-on-debian-9-stretch
• https://github.com/mvo5/unattended-upgrades
• https://wiki.debian.org/UnattendedUpgrades#apt-listchanges
• https://www.cyberciti.biz/faq/apt-get-apticron-send-email-upgrades-available/
• https://www.unixmen.com/how-to-get-email-notifications-for-new-updates-on-debianubuntu/
• /etc/apt/apt.conf.d/50unattended-upgrades

Steps

Install unattended-upgrades, apt-listchanges, and apticron:

sudo apt install unattended-upgrades apt-listchanges apticron

Now we need to configure unattended-upgrades to automatically apply the updates. This is typically done by editing the files /etc/apt/apt.conf.d/20auto-upgrades and /etc/apt/apt.conf.d/50unattended-upgrades that were created by the packages. However, because these file may get overwritten with a future update, we'll create a new file instead. Create the file /etc/apt/apt.conf.d/51myunattended-upgrades and add this:

// Enable the update/upgrade script (0=disable)
APT::Periodic::Enable "1";

// Do "apt-get update" automatically every n-days (0=disable)
APT::Periodic::Update-Package-Lists "1";

// Do "apt-get upgrade --download-only" every n-days (0=disable)
APT::Periodic::Download-Upgradeable-Packages "1";

// Do "apt-get autoclean" every n-days (0=disable)
APT::Periodic::AutocleanInterval "7";

// Send report mail to root
//     0:  no report             (or null string)
//     1:  progress report       (actually any string)
//     2:  + command outputs     (remove -qq, remove 2>/dev/null, add -d)
//     3:  + trace on    APT::Periodic::Verbose "2";
APT::Periodic::Unattended-Upgrade "1";

// Automatically upgrade packages from these
Unattended-Upgrade::Origins-Pattern {
      "o=Debian,a=stable";
      "o=Debian,a=stable-updates";
      "origin=Debian,codename=${distro_codename},label=Debian-Security";
};

// You can specify your own packages to NOT automatically upgrade here
Unattended-Upgrade::Package-Blacklist {
};

// Run dpkg --force-confold --configure -a if a unclean dpkg state is detected to true to ensure that updates get installed even when the system got interrupted during a previous run
Unattended-Upgrade::AutoFixInterruptedDpkg "true";

//Perform the upgrade when the machine is running because we wont be shutting our server down often
Unattended-Upgrade::InstallOnShutdown "false";

// Send an email to this address with information about the packages upgraded.
Unattended-Upgrade::Mail "root";

// Always send an e-mail
Unattended-Upgrade::MailOnlyOnError "false";

// Remove all unused dependencies after the upgrade has finished
Unattended-Upgrade::Remove-Unused-Dependencies "true";

// Remove any new unused dependencies after the upgrade has finished
Unattended-Upgrade::Remove-New-Unused-Dependencies "true";

// Automatically reboot WITHOUT CONFIRMATION if the file /var/run/reboot-required is found after the upgrade.
Unattended-Upgrade::Automatic-Reboot "true";

// Automatically reboot even if users are logged in.
Unattended-Upgrade::Automatic-Reboot-WithUsers "true";

Notes:

• Check /usr/lib/apt/apt.systemd.daily for details on the APT::Periodic options
• Check https://github.com/mvo5/unattended-upgrades for details on the Unattended-Upgrade options

Run a dry-run of unattended-upgrades to make sure your configuration file is okay:

sudo unattended-upgrade -d --dry-run

If everything is okay, you can let it run whenever it's scheduled to or force a run with unattended-upgrade -d.

Configure apt-listchanges to your liking:

sudo dpkg-reconfigure apt-listchanges

For apticron, the default settings are good enough but you can check them in /etc/apticron/apticron.conf if you want to change them. For example, my configuration looks like this:

EMAIL="root"
NOTIFY_NO_UPDATES="1"

More Secure Random Entropy Pool (WIP)

Why

WIP

How It Works

WIP

Goals

WIP

References

• Thanks to branneman for this idea as submitted in issue #33.
• https://hackaday.com/2017/11/02/what-is-entropy-and-how-do-i-get-more-of-it/
• https://www.2uo.de/myths-about-urandom
• https://www.gnu.org/software/hurd/user/tlecarrour/rng-tools.html
• https://wiki.archlinux.org/index.php/Rng-tools
• https://www.howtoforge.com/helping-the-random-number-generator-to-gain-enough-entropy-with-rng-tools-debian-lenny
• https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/security_guide/sect-security_guide-encryption-using_the_random_number_generator

Steps

Install rng-tools.

On Debian based systems:

sudo apt-get install rng-tools

Now we need to set the hardware device used to generate random numbers by adding this to /etc/default/rng-tools:

HRNGDEVICE=/dev/urandom

For the lazy:

echo "HRNGDEVICE=/dev/urandom" | sudo tee -a /etc/default/rng-tools

Restart the service:

sudo systemctl stop rng-tools.service
sudo systemctl start rng-tools.service

Test randomness:

• https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/6/html/security_guide/sect-security_guide-encryption-using_the_random_number_generator
• https://wiki.archlinux.org/index.php/Rng-tools

The Network

Firewall With UFW (Uncomplicated Firewall)

Why

Call me paranoid, and you don't have to agree, but I want to deny all traffic in and out of my server except what I explicitly allow. Why would my server be sending traffic out that I don't know about? And why would external traffic be trying to access my server if I don't know who or what it is? When it comes to good security, my opinion is to reject/deny by default, and allow by exception.

Of course, if you disagree, that is totally fine and can configure UFW to suit your needs.

Either way, ensuring that only traffic we explicitly allow is the job of a firewall.

How It Works

The Linux kernel provides capabilities to monitor and control network traffic. These capabilities are exposed to the end-user through firewall utilities. On Linux, the most common firewall is iptables. However, iptables is rather complicated and confusing (IMHO). This is where UFW comes in. Think of UFW as a front-end to iptables. It simplifies the process of managing the iptables rules that tell the Linux kernel what to do with network traffic.

UFW works by letting you configure rules that:

• allow or deny
• input or output traffic
• to or from ports

You can create rules by explicitly specifying the ports or with application configurations that specify the ports.

Goals

• all network traffic, input and output, blocked except those we explicitly allow

Notes

• As you install other programs, you'll need to enable the necessary ports/applications.

References

• https://launchpad.net/ufw

Steps

Install ufw.

On Debian based systems:

sudo apt install ufw

Deny all outgoing traffic:

sudo ufw default deny outgoing comment 'deny all outgoing traffic'

Default outgoing policy changed to 'deny'
(be sure to update your rules accordingly)

If you are not as paranoid as me, and don't want to deny all outgoing traffic, you can allow it instead:

sudo ufw default allow outgoing comment 'allow all outgoing traffic'

Deny all incoming traffic:

sudo ufw default deny incoming comment 'deny all incoming traffic'

Obviously we want SSH connections in:

sudo ufw limit in ssh comment 'allow SSH connections in'

Rules updated
Rules updated (v6)

Allow additional traffic as per your needs. Some common use-cases:

# allow traffic out on port 53 -- DNS
sudo ufw allow out 53 comment 'allow DNS calls out'

# allow traffic out on port 123 -- NTP
sudo ufw allow out 123 comment 'allow NTP out'

# allow traffic out for HTTP, HTTPS, or FTP
# apt might needs these depending on which sources you're using
sudo ufw allow out http comment 'allow HTTP traffic out'
sudo ufw allow out https comment 'allow HTTPS traffic out'
sudo ufw allow out ftp comment 'allow FTP traffic out'

# allow whois
sudo ufw allow out whois comment 'allow whois'

# allow traffic out on port 68 -- the DHCP client
# you only need this if you're using DHCP
sudo ufw allow out 67 comment 'allow the DHCP client to update'
sudo ufw allow out 68 comment 'allow the DHCP client to update'

Start ufw:

sudo ufw enable

Command may disrupt existing ssh connections. Proceed with operation (y|n)? y
Firewall is active and enabled on system startup

If you want to see a status:

sudo ufw status

Status: active

To                         Action      From
--                         ------      ----
22/tcp                     LIMIT       Anywhere                   # allow SSH connections in
22/tcp (v6)                LIMIT       Anywhere (v6)              # allow SSH connections in

53                         ALLOW OUT   Anywhere                   # allow DNS calls out
123                        ALLOW OUT   Anywhere                   # allow NTP out
80/tcp                     ALLOW OUT   Anywhere                   # allow HTTP traffic out
443/tcp                    ALLOW OUT   Anywhere                   # allow HTTPS traffic out
21/tcp                     ALLOW OUT   Anywhere                   # allow FTP traffic out
Mail submission            ALLOW OUT   Anywhere                   # allow mail out
43/tcp                     ALLOW OUT   Anywhere                   # allow whois
53 (v6)                    ALLOW OUT   Anywhere (v6)              # allow DNS calls out
123 (v6)                   ALLOW OUT   Anywhere (v6)              # allow NTP out
80/tcp (v6)                ALLOW OUT   Anywhere (v6)              # allow HTTP traffic out
443/tcp (v6)               ALLOW OUT   Anywhere (v6)              # allow HTTPS traffic out
21/tcp (v6)                ALLOW OUT   Anywhere (v6)              # allow FTP traffic out
Mail submission (v6)       ALLOW OUT   Anywhere (v6)              # allow mail out
43/tcp (v6)                ALLOW OUT   Anywhere (v6)              # allow whois

or

sudo ufw status verbose

Status: active
Logging: on (low)
Default: deny (incoming), deny (outgoing), disabled (routed)
New profiles: skip

To                         Action      From
--                         ------      ----
22/tcp                     LIMIT IN    Anywhere                   # allow SSH connections in
22/tcp (v6)                LIMIT IN    Anywhere (v6)              # allow SSH connections in

53                         ALLOW OUT   Anywhere                   # allow DNS calls out
123                        ALLOW OUT   Anywhere                   # allow NTP out
80/tcp                     ALLOW OUT   Anywhere                   # allow HTTP traffic out
443/tcp                    ALLOW OUT   Anywhere                   # allow HTTPS traffic out
21/tcp                     ALLOW OUT   Anywhere                   # allow FTP traffic out
587/tcp (Mail submission)  ALLOW OUT   Anywhere                   # allow mail out
43/tcp                     ALLOW OUT   Anywhere                   # allow whois
53 (v6)                    ALLOW OUT   Anywhere (v6)              # allow DNS calls out
123 (v6)                   ALLOW OUT   Anywhere (v6)              # allow NTP out
80/tcp (v6)                ALLOW OUT   Anywhere (v6)              # allow HTTP traffic out
443/tcp (v6)               ALLOW OUT   Anywhere (v6)              # allow HTTPS traffic out
21/tcp (v6)                ALLOW OUT   Anywhere (v6)              # allow FTP traffic out
587/tcp (Mail submission (v6)) ALLOW OUT   Anywhere (v6)              # allow mail out
43/tcp (v6)                ALLOW OUT   Anywhere (v6)              # allow whois

Default Applications

ufw ships with some default applications. You can see them with:

sudo ufw app list

Available applications:
  AIM
  Bonjour
  CIFS
  DNS
  Deluge
  IMAP
  IMAPS
  IPP
  KTorrent
  Kerberos Admin
  Kerberos Full
  Kerberos KDC
  Kerberos Password
  LDAP
  LDAPS
  LPD
  MSN
  MSN SSL
  Mail submission
  NFS
  OpenSSH
  POP3
  POP3S
  PeopleNearby
  SMTP
  SSH
  Socks
  Telnet
  Transmission
  Transparent Proxy
  VNC
  WWW
  WWW Cache
  WWW Full
  WWW Secure
  XMPP
  Yahoo
  qBittorrent
  svnserve

To get details about the app, like which ports it includes, type:

sudo ufw app info [app name]

sudo ufw app info DNS

Profile: DNS
Title: Internet Domain Name Server
Description: Internet Domain Name Server

Port:
  53

Custom Application

If you don't want to create rules by explicitly providing the port number(s), you can create your own application configurations. To do this, create a file in /etc/ufw/applications.d.

For example, here is what you would use for Plex:

cat /etc/ufw/applications.d/plexmediaserver

[PlexMediaServer]
title=Plex Media Server
description=This opens up PlexMediaServer for http (32400), upnp, and autodiscovery.
ports=32469/tcp|32413/udp|1900/udp|32400/tcp|32412/udp|32410/udp|32414/udp|32400/udp

Then you can enable it like any other app:

sudo ufw allow plexmediaserver

iptables Intrusion Detection And Prevention with PSAD

Why

Even if you have a firewall to guard your doors, it is possible to try brute-forcing your way in any of the guarded doors. We want to monitor all network activity to detect potential intrusion attempts, such has repeated attempts to get in, and block them.

How It Works

I can't explain it any better than user FINESEC from https://serverfault.com/ did at: https://serverfault.com/a/447604/289829.

Fail2BAN scans log files of various applications such as apache, ssh or ftp and automatically bans IPs that show the malicious signs such as automated login attempts. PSAD on the other hand scans iptables and ip6tables log messages (typically /var/log/messages) to detect and optionally block scans and other types of suspect traffic such as DDoS or OS fingerprinting attempts. It's ok to use both programs at the same time because they operate on different level.

And, since we're already using UFW so we'll follow the awesome instructions by netson at https://gist.github.com/netson/c45b2dc4e835761fbccc to make PSAD work with UFW.

References

• http://www.cipherdyne.org/psad/
• http://www.cipherdyne.org/psad/docs/config.html
• https://www.thefanclub.co.za/how-to/how-install-psad-intrusion-detection-ubuntu-1204-lts-server
• https://serverfault.com/a/447604/289829
• https://serverfault.com/a/770424/289829
• https://gist.github.com/netson/c45b2dc4e835761fbccc
• Thanks to sysadt for catching the issue (#61) with psadwatchd.

Steps

Install psad.

On Debian based systems:

sudo apt install psad

Make a backup of psad's configuration file /etc/psad/psad.conf:

sudo cp --archive /etc/psad/psad.conf /etc/psad/psad.conf-COPY-$(date +"%Y%m%d%H%M%S")

Review and update configuration options in /etc/psad/psad.conf. Pay special attention to these:

Setting	Set To
EMAIL_ADDRESSES	your email address(s)
HOSTNAME	your server's hostname
ENABLE_PSADWATCHD	ENABLE_PSADWATCHD Y;
ENABLE_AUTO_IDS	ENABLE_AUTO_IDS Y;
ENABLE_AUTO_IDS_EMAILS	ENABLE_AUTO_IDS_EMAILS Y;
EXPECT_TCP_OPTIONS	EXPECT_TCP_OPTIONS Y;

Check the configuration file psad's documentation at http://www.cipherdyne.org/psad/docs/config.html for more details.

Now we need to make some changes to ufw so it works with psad by telling ufw to log all traffic so psad can analyze it. Do this by editing two files and adding these lines at the end but before the COMMIT line.

Make backups:

sudo cp --archive /etc/ufw/before.rules /etc/ufw/before.rules-COPY-$(date +"%Y%m%d%H%M%S")
sudo cp --archive /etc/ufw/before6.rules /etc/ufw/before6.rules-COPY-$(date +"%Y%m%d%H%M%S")

Edit the files:

• /etc/ufw/before.rules
• /etc/ufw/before6.rules

Now we need to reload/restart ufw and psad for the changes to take effect:

sudo ufw reload

sudo psad -R
sudo psad --sig-update
sudo psad -H

Analyze iptables rules for errors:

sudo psad --fw-analyze

[+] Parsing INPUT chain rules.
[+] Parsing INPUT chain rules.
[+] Firewall config looks good.
[+] Completed check of firewall ruleset.
[+] Results in /var/log/psad/fw_check
[+] Exiting.

Note: If there were any issues you will get an e-mail with the error.

Check the status of psad:

sudo psad --Status

[-] psad: pid file /var/run/psad/psadwatchd.pid does not exist for psadwatchd on vm
[+] psad_fw_read (pid: 3444)  %CPU: 0.0  %MEM: 2.2
    Running since: Sat Feb 16 01:03:09 2019

[+] psad (pid: 3435)  %CPU: 0.2  %MEM: 2.7
    Running since: Sat Feb 16 01:03:09 2019
    Command line arguments: [none specified]
    Alert email address(es): root@localhost

[+] Version: psad v2.4.3

[+] Top 50 signature matches:
        [NONE]

[+] Top 25 attackers:
        [NONE]

[+] Top 20 scanned ports:
        [NONE]

[+] iptables log prefix counters:
        [NONE]

    Total protocol packet counters:

[+] IP Status Detail:
        [NONE]

    Total scan sources: 0
    Total scan destinations: 0

[+] These results are available in: /var/log/psad/status.out

Application Intrusion Detection And Prevention With Fail2Ban

Why

UFW tells your server what doors to board up so nobody can see them, and what doors to allow authorized users through. PSAD monitors network activity to detect and prevent potential intrusions -- repeated attempts to get in.

But what about the applications/services your server is running, like SSH and Apache, where your firewall is configured to allow access in. Even though access may be allowed that doesn't mean all access attempts are valid and harmless. What if someone tries to brute-force their way in to a web-app you're running on your server? This is where Fail2ban comes in.

How It Works

Fail2ban monitors the logs of your applications (like SSH and Apache) to detect and prevent potential intrusions. It will monitor network traffic/logs and prevent intrusions by blocking suspicious activity (e.g. multiple successive failed connections in a short time-span).

Goals

• network monitoring for suspicious activity with automatic banning of offending IPs

Notes

• As of right now, the only thing running on this server is SSH so we'll want Fail2ban to monitor SSH and ban as necessary.
• As you install other programs, you'll need to create/configure the appropriate jails and enable them.

References

• https://www.fail2ban.org/
• https://blog.vigilcode.com/2011/05/ufw-with-fail2ban-quick-secure-setup-part-ii/
• https://dodwell.us/security/ufw-fail2ban-portscan.html
• https://www.howtoforge.com/community/threads/fail2ban-and-ufw-on-debian.77261/

Steps

Install fail2ban.

On Debian based systems:

sudo apt install fail2ban

We don't want to edit /etc/fail2ban/fail2ban.conf or /etc/fail2ban/jail.conf because a future update may overwrite those so we'll create a local copy instead. Create the file /etc/fail2ban/jail.local and add this to it after replacing [LAN SEGMENT] and [your email] with the appropriate values:

[DEFAULT]
# the IP address range we want to ignore
ignoreip = 127.0.0.1/8 [LAN SEGMENT]

# who to send e-mail to
destemail = [your e-mail]

# who is the email from
sender = [your e-mail]

# since we're using exim4 to send emails
mta = mail

# get email alerts
action = %(action_mwl)s

Note: Your server will need to be able to send e-mails so Fail2ban can let you know of suspicious activity and when it banned an IP.

We need to create a jail for SSH that tells fail2ban to look at SSH logs and use ufw to ban/unban IPs as needed. Create a jail for SSH by creating the file /etc/fail2ban/jail.d/ssh.local and adding this to it:

[sshd]
enabled = true
banaction = ufw
port = ssh
filter = sshd
logpath = %(sshd_log)s
maxretry = 5

For the lazy:

cat << EOF | sudo tee /etc/fail2ban/jail.d/ssh.local
[sshd]
enabled = true
banaction = ufw
port = ssh
filter = sshd
logpath = %(sshd_log)s
maxretry = 5
EOF

In the above we tell fail2ban to use the ufw as the banaction. Fail2ban ships with an action configuration file for ufw. You can see it in /etc/fail2ban/action.d/ufw.conf

Enable fail2ban:

sudo fail2ban-client start
sudo fail2ban-client reload
sudo fail2ban-client add sshd # This may fail on some systems if the sshd jail was added by default

To check the status:

sudo fail2ban-client status

Status
|- Number of jail:      1
`- Jail list:   sshd

sudo fail2ban-client status sshd

Status for the jail: sshd
|- Filter
|  |- Currently failed: 0
|  |- Total failed:     0
|  `- File list:        /var/log/auth.log
`- Actions
   |- Currently banned: 0
   |- Total banned:     0
   `- Banned IP list:

Custom Jails

I have not needed to create a custom jail yet. Once I do, and I figure out how, I will update this guide. Or, if you know how please help contribute.

Unban an IP

To unban an IP use this command:

fail2ban-client set [jail] unbanip [IP]

[jail] is the name of the jail that has the banned IP and [IP] is the IP address you want to unban. For example, to unaban 192.168.1.100 from SSH you would do:

fail2ban-client set sshd unbanip 192.168.1.100

The Auditing

File/Folder Integrity Monitoring With AIDE (WIP)

Why

WIP

How It Works

WIP

Goals

WIP

References

• https://aide.github.io/
• https://www.hiroom2.com/2017/06/09/debian-8-file-integrity-check-with-aide/
• https://blog.rapid7.com/2017/06/30/how-to-install-and-configure-aide-on-ubuntu-linux/
• https://www.stephenrlang.com/2016/03/using-aide-for-file-integrity-monitoring-fim-on-ubuntu/
• https://www.howtoforge.com/how-to-configure-the-aide-advanced-intrusion-detection-environment-file-integrity-scanner-for-your-website
• https://www.tecmint.com/check-integrity-of-file-and-directory-using-aide-in-linux/
• https://www.cyberciti.biz/faq/debian-ubuntu-linux-software-integrity-checking-with-aide/

Steps

Install AIDE.

On Debian based systems:

sudo apt install aide

Make a backup of AIDE's defaults file:

sudo cp -p /etc/default/aide /etc/default/aide-COPY-$(date +"%Y%m%d%H%M%S")

Go through /etc/default/aide and set AIDE's defaults per your requirements. If you want AIDE to run daily and e-mail you, be sure to set CRON_DAILY_RUN to yes.

Make a backup of AIDE's configuration files:

sudo cp -pr /etc/aide /etc/aide-COPY-$(date +"%Y%m%d%H%M%S")

On Debian based systems:

• AIDE's configuration files are in /etc/aide/aide.conf.d/.
• You'll want to go through AIDE's documentation and the configuration files in to set them per your requirements.
• If you want new settings, to monitor a new folder for example, you'll want to add them to /etc/aide/aide.conf or /etc/aide/aide.conf.d/.
• Take a backup of the stock configuration files: sudo cp -pr /etc/aide /etc/aide-COPY-$(date +"%Y%m%d%H%M%S").

Create a new database, and install it.

On Debian based systems:

sudo aideinit

Running aide --init...
Start timestamp: 2019-04-01 21:23:37 -0400 (AIDE 0.16)
AIDE initialized database at /var/lib/aide/aide.db.new
Verbose level: 6

Number of entries:      25973

---------------------------------------------------
The attributes of the (uncompressed) database(s):
---------------------------------------------------

/var/lib/aide/aide.db.new
  RMD160   : moyQ1YskQQbidX+Lusv3g2wf1gQ=
  TIGER    : 7WoOgCrXzSpDrlO6I3PyXPj1gRiaMSeo
  SHA256   : gVx8Fp7r3800WF2aeXl+/KHCzfGsNi7O
             g16VTPpIfYQ=
  SHA512   : GYfa0DJwWgMLl4Goo5VFVOhu4BphXCo3
             rZnk49PYztwu50XjaAvsVuTjJY5uIYrG
             tV+jt3ELvwFzGefq4ZBNMg==
  CRC32    : /cusZw==
  HAVAL    : E/i5ceF3YTjwenBfyxHEsy9Kzu35VTf7
             CPGQSW4tl14=
  GOST     : n5Ityzxey9/1jIs7LMc08SULF1sLBFUc
             aMv7Oby604A=


End timestamp: 2019-04-01 21:24:45 -0400 (run time: 1m 8s)

Test everything works with no changes.

On Debian based systems:

sudo aide.wrapper --check

Start timestamp: 2019-04-01 21:24:45 -0400 (AIDE 0.16)
AIDE found NO differences between database and filesystem. Looks okay!!
Verbose level: 6

Number of entries:      25973

---------------------------------------------------
The attributes of the (uncompressed) database(s):
---------------------------------------------------

/var/lib/aide/aide.db
  RMD160   : moyQ1YskQQbidX+Lusv3g2wf1gQ=
  TIGER    : 7WoOgCrXzSpDrlO6I3PyXPj1gRiaMSeo
  SHA256   : gVx8Fp7r3800WF2aeXl+/KHCzfGsNi7O
             g16VTPpIfYQ=
  SHA512   : GYfa0DJwWgMLl4Goo5VFVOhu4BphXCo3
             rZnk49PYztwu50XjaAvsVuTjJY5uIYrG
             tV+jt3ELvwFzGefq4ZBNMg==
  CRC32    : /cusZw==
  HAVAL    : E/i5ceF3YTjwenBfyxHEsy9Kzu35VTf7
             CPGQSW4tl14=
  GOST     : n5Ityzxey9/1jIs7LMc08SULF1sLBFUc
             aMv7Oby604A=


End timestamp: 2019-04-01 21:26:03 -0400 (run time: 1m 18s)

Test everything works after making some changes.

On Debian based systems:

sudo touch /etc/test.sh
sudo touch /root/test.sh

sudo aide.wrapper --check

sudo rm /etc/test.sh
sudo rm /root/test.sh

sudo aideinit -y -f

Start timestamp: 2019-04-01 21:37:37 -0400 (AIDE 0.16)
AIDE found differences between database and filesystem!!
Verbose level: 6

Summary:
  Total number of entries:      25972
  Added entries:                2
  Removed entries:              0
  Changed entries:              1

---------------------------------------------------
Added entries:
---------------------------------------------------

f++++++++++++++++: /etc/test.sh
f++++++++++++++++: /root/test.sh

---------------------------------------------------
Changed entries:
---------------------------------------------------

d =.... mc.. .. .: /root

---------------------------------------------------
Detailed information about changes:
---------------------------------------------------

Directory: /root
  Mtime    : 2019-04-01 21:35:07 -0400        | 2019-04-01 21:37:36 -0400
  Ctime    : 2019-04-01 21:35:07 -0400        | 2019-04-01 21:37:36 -0400


---------------------------------------------------
The attributes of the (uncompressed) database(s):
---------------------------------------------------

/var/lib/aide/aide.db
  RMD160   : qF9WmKaf2PptjKnhcr9z4ueCPTY=
  TIGER    : zMo7MvvYJcq1hzvTQLPMW7ALeFiyEqv+
  SHA256   : LSLLVjjV6r8vlSxlbAbbEsPcQUB48SgP
             pdVqEn6ZNbQ=
  SHA512   : Qc4U7+ZAWCcitapGhJ1IrXCLGCf1IKZl
             02KYL1gaZ0Fm4dc7xLqjiquWDMSEbwzW
             oz49NCquqGz5jpMIUy7UxA==
  CRC32    : z8ChEA==
  HAVAL    : YapzS+/cdDwLj3kHJEq8fufLp3DPKZDg
             U12KCSkrO7Y=
  GOST     : 74sLV4HkTig+GJhokvxZQm7CJD/NR0mG
             6jV7zdt5AXQ=


End timestamp: 2019-04-01 21:38:50 -0400 (run time: 1m 13s)

That's it. If you set CRON_DAILY_RUN to yes in /etc/default/aide then cron will execute /etc/cron.daily/aide every day and e-mail you the output.

Updating The Database

Every time you make changes to files/folders that AIDE monitors, you will need to update the database to capture those changes. To do that on Debian based systems:

sudo aideinit -y -f

Anti-Virus Scanning With ClamAV (WIP)

Why

WIP

How It Works

• ClamAV is a virus scanner
• ClamAV-Freshclam is a service that keeps the virus definitions updated
• ClamAV-Daemon keeps the clamd process running to make scanning faster

Goals

WIP

Notes

• These instructions do not tell you how to enable the ClamAV daemon service to ensure clamd is running all the time. clamd is only if you're running a mail server and does not provide real-time monitoring of files. Instead, you'd want to scan files manually or on a schedule.

References

• https://www.clamav.net/documents/installation-on-debian-and-ubuntu-linux-distributions
• https://wiki.debian.org/ClamAV
• https://www.osradar.com/install-clamav-debian-9-ubuntu-18/
• https://www.lisenet.com/2014/automate-clamav-to-perform-daily-system-scan-and-send-email-notifications-on-linux/
• https://www.howtoforge.com/tutorial/configure-clamav-to-scan-and-notify-virus-and-malware/
• https://serverfault.com/questions/741299/is-there-a-way-to-keep-clamav-updated-on-debian-8
• https://askubuntu.com/questions/250290/how-do-i-scan-for-viruses-with-clamav
• https://ngothang.com/how-to-install-clamav-and-configure-daily-scanning-on-centos/

Steps

Install ClamAV.

On Debian based systems:

sudo apt install clamav clamav-freshclam clamav-daemon

Make a backup of clamav-freshclam's configuration file /etc/clamav/freshclam.conf:

sudo cp --archive /etc/clamav/freshclam.conf /etc/clamav/freshclam.conf-COPY-$(date +"%Y%m%d%H%M%S")

clamav-freshclam's default settings are probably good enough but if you want to change them, you can either edit the file /etc/clamav/freshclam.conf or use dpkg-reconfigure:

sudo dpkg-reconfigure clamav-freshclam

Note: The default settings will update the definitions 24 times in a day. To change the interval, check the Checks setting in /etc/clamav/freshclam.conf or use dpkg-reconfigure.

Start the clamav-freshclam service:

sudo service clamav-freshclam start

You can make sure clamav-freshclam running:

sudo service clamav-freshclam status

● clamav-freshclam.service - ClamAV virus database updater
   Loaded: loaded (/lib/systemd/system/clamav-freshclam.service; enabled; vendor preset: enabled)   Active: active (running) since Sat 2019-03-16 22:57:07 EDT; 2min 13s ago
     Docs: man:freshclam(1)
           man:freshclam.conf(5)
           https://www.clamav.net/documents
 Main PID: 1288 (freshclam)
   CGroup: /system.slice/clamav-freshclam.service
           └─1288 /usr/bin/freshclam -d --foreground=true

Mar 16 22:57:08 host freshclam[1288]: Sat Mar 16 22:57:08 2019 -> ^Local version: 0.100.2 Recommended version: 0.101.1
Mar 16 22:57:08 host freshclam[1288]: Sat Mar 16 22:57:08 2019 -> DON'T PANIC! Read https://www.clamav.net/documents/upgrading-clamav
Mar 16 22:57:15 host freshclam[1288]: Sat Mar 16 22:57:15 2019 -> Downloading main.cvd [100%]
Mar 16 22:57:38 host freshclam[1288]: Sat Mar 16 22:57:38 2019 -> main.cvd updated (version: 58, sigs: 4566249, f-level: 60, builder: sigmgr)
Mar 16 22:57:40 host freshclam[1288]: Sat Mar 16 22:57:40 2019 -> Downloading daily.cvd [100%]
Mar 16 22:58:13 host freshclam[1288]: Sat Mar 16 22:58:13 2019 -> daily.cvd updated (version: 25390, sigs: 1520006, f-level: 63, builder: raynman)
Mar 16 22:58:14 host freshclam[1288]: Sat Mar 16 22:58:14 2019 -> Downloading bytecode.cvd [100%]
Mar 16 22:58:16 host freshclam[1288]: Sat Mar 16 22:58:16 2019 -> bytecode.cvd updated (version: 328, sigs: 94, f-level: 63, builder: neo)
Mar 16 22:58:24 host freshclam[1288]: Sat Mar 16 22:58:24 2019 -> Database updated (6086349 signatures) from db.local.clamav.net (IP: 104.16.219.84)
Mar 16 22:58:24 host freshclam[1288]: Sat Mar 16 22:58:24 2019 -> ^Clamd was NOT notified: Can't connect to clamd through /var/run/clamav/clamd.ctl: No such file or directory

Note: Don't worry about that Local version line. Check https://serverfault.com/questions/741299/is-there-a-way-to-keep-clamav-updated-on-debian-8 for more details.

Make a backup of clamav-daemon's configuration file /etc/clamav/clamd.conf:

sudo cp --archive /etc/clamav/clamd.conf /etc/clamav/clamd.conf-COPY-$(date +"%Y%m%d%H%M%S")

You can change clamav-daemon's settings by editing the file /etc/clamav/clamd.conf or useing dpkg-reconfigure:

sudo dpkg-reconfigure clamav-daemon

Scanning Files/Folders

• To scan files/folders use the clamscan program.
• clamscan runs as the user it is executed as so it needs read permissions to the files/folders it is scanning.
• Using clamscan as root is dangerous because if a file is in fact a virus there is risk that it could use the root privileges.
• To scan a file: clamscan /path/to/file.
• To scan a directory: clamscan -r /path/to/folder.
• You can use the -i switch to only print infected files.
• Check clamscan's man pages for other switches/options.

Rootkit Detection With Rkhunter (WIP)

Why

WIP

How It Works

WIP

Goals

WIP

References

• http://rkhunter.sourceforge.net/
• https://www.cyberciti.biz/faq/howto-check-linux-rootkist-with-detectors-software/
• https://www.tecmint.com/install-rootkit-hunter-scan-for-rootkits-backdoors-in-linux/

Steps

Install Rkhunter.

On Debian based systems:

sudo apt install rkhunter

Make a backup of rkhunter' defaults file:

sudo cp -p /etc/default/rkhunter /etc/default/rkhunter-COPY-$(date +"%Y%m%d%H%M%S")

rkhunter's configuration file is /etc/rkhunter.conf. Instead of making changes to it, create and use the file /etc/rkhunter.conf.local instead:

sudo cp -p /etc/rkhunter.conf /etc/rkhunter.conf.local

Go through the configuration file /etc/rkhunter.conf.local and set to your requirements. My recommendations:

Setting	Note
UPDATE_MIRRORS=1
MIRRORS_MODE=0
MAIL-ON-WARNING=root
COPY_LOG_ON_ERROR=1	to save a copy of the log if there is an error
PKGMGR=...	set to the appropriate value per the documentation
PHALANX2_DIRTEST=1	read the documentation for why
WEB_CMD=""	this is to address an issue with the Debian package that disables the ability for rkhunter to self-update.
USE_LOCKING=1	to prevent issues with rkhunter running multiple times
SHOW_SUMMARY_WARNINGS_NUMBER=1	to see the actual number of warnings found

You want rkhunter to run every day and e-mail you the result. You can write your own script or check https://www.tecmint.com/install-rootkit-hunter-scan-for-rootkits-backdoors-in-linux/ for a sample cron script you can use.

On Debian based system, rkhunter comes with cron scripts. To enable them check /etc/default/rkhunter or use dpkg-reconfigure and say Yes to all of the questions:

sudo dpkg-reconfigure rkhunter

After you've finished with all of the changes, make sure all the settings are valid:

sudo rkhunter -C

Update rkhunter and its database:

sudo rkhunter --versioncheck
sudo rkhunter --update
sudo rkhunter --propupd

If you want to do a manual scan and see the output:

sudo rkhunter --check

Rootkit Detection With chrootkit (WIP)

Why

WIP

How It Works

WIP

Goals

WIP

References

• http://www.chkrootkit.org/
• https://www.cyberciti.biz/faq/howto-check-linux-rootkist-with-detectors-software/
• https://askubuntu.com/questions/258658/eth0-packet-sniffer-sbin-dhclient

Steps

Install chkrootkit.

On Debian based systems:

sudo apt install chkrootkit

Do a manual scan:

sudo chkrootkit

ROOTDIR is `/'
Checking `amd'...                                           not found
Checking `basename'...                                      not infected
Checking `biff'...                                          not found
Checking `chfn'...                                          not infected
Checking `chsh'...                                          not infected
...
Checking `scalper'...                                       not infected
Checking `slapper'...                                       not infected
Checking `z2'...                                            chklastlog: nothing deleted
Checking `chkutmp'...                                       chkutmp: nothing deleted
Checking `OSX_RSPLUG'...                                    not infected

Make a backup of chkrootkit's configuration file /etc/chkrootkit.conf:

sudo cp --archive /etc/chkrootkit.conf /etc/chkrootkit.conf-COPY-$(date +"%Y%m%d%H%M%S")

You want chkrootkit to run every day and e-mail you the result.

On Debian based system, chkrootkit comes with cron scripts. To enable them check /etc/chkrootkit.conf or use dpkg-reconfigure and say Yes to the first question:

sudo dpkg-reconfigure chkrootkit

logwatch - system log analyzer and reporter

Why

Your server will be generating a lot of logs that may contain important information. Unless you plan on checking your server everyday, you'll want a way to get e-mail summary of your server's logs. To accomplish this we'll use logwatch.

How It Works

logwatch scans system log files and summarizes them. You can run it directly from the command line or schedule it to run on a recurring schedule. logwatch uses service files to know how to read/summarize a log file. You can see all of the stock service files in /usr/share/logwatch/scripts/services.

logwatch's configuration file /usr/share/logwatch/default.conf/logwatch.conf specifies default options. You can override them via command line arguments.

Goals

• Logwatch configured to send a daily e-mail summary of all of the server's status and logs

Notes

• Your server will need to be able to send e-mails for this to work
• The below steps will result in logwatch running every day. If you want to change the schedule, modify the cronjob to your liking. You'll also want to change the range option to cover your recurrence window. See https://www.badpenguin.org/configure-logwatch-for-weekly-email-and-html-output-format for an example.
• If logwatch fails to deliver mail due to the e-mail having long lines please check https://blog.dhampir.no/content/exim4-line-length-in-debian-stretch-mail-delivery-failed-returning-message-to-sender as documented in issue #29. If you you followed Gmail and Exim4 As MTA With Implicit TLS then we already took care of this in step #7.

References

• Thanks to amacheema for fixing some issues with the steps and letting me know of a long line bug with exim4 as documented in issue #29.
• https://sourceforge.net/projects/logwatch/
• https://www.digitalocean.com/community/tutorials/how-to-install-and-use-logwatch-log-analyzer-and-reporter-on-a-vps

Steps

Install logwatch.

On Debian based systems:

sudo apt install logwatch

To see a sample of what logwatch collects you can run it directly:

sudo /usr/sbin/logwatch --output stdout --format text --range yesterday --service all

 ################### Logwatch 7.4.3 (12/07/16) ####################
        Processing Initiated: Mon Mar  4 00:05:50 2019
        Date Range Processed: yesterday
                              ( 2019-Mar-03 )
                              Period is day.
        Detail Level of Output: 5
        Type of Output/Format: stdout / text
        Logfiles for Host: host
 ##################################################################

 --------------------- Cron Begin ------------------------
...
...
 ---------------------- Disk Space End -------------------------


 ###################### Logwatch End #########################

Go through logwatch's self-documented configuration file /usr/share/logwatch/default.conf/logwatch.conf before continuing. There is no need to change anything here but pay special attention to the Output, Format, MailTo, Range, and Service as those are the ones we'll be using. For our purposes, instead of specifying our options in the configuration file, we will pass them as command line arguments in the daily cron job that executes logwatch. That way, if the configuration file is ever modified (e.g. during an update), our options will still be there.

Make a backup of logwatch's daily cron file /etc/cron.daily/00logwatch and unset the execute bit:

sudo cp --archive /etc/cron.daily/00logwatch /etc/cron.daily/00logwatch-COPY-$(date +"%Y%m%d%H%M%S")
sudo chmod -x /etc/cron.daily/00logwatch-COPY*

By default, logwatch outputs to stdout. Since the goal is to get a daily e-mail, we need to change the output type that logwatch uses to send e-mail instead. We could do this through the configuration file above, but that would apply to every time it is run -- even when we run it manually and want to see the output to the screen. Instead, we'll change the cron job that executes logwatch to send e-mail. This way, when run manually, we'll still get output to stdout and when run by cron, it'll send an e-mail. We'll also make sure it checks for all services, and change the output format to html so it's easier to read regardless of what the configuration file says. In the file /etc/cron.daily/00logwatch find the execute line and change it to:

/usr/sbin/logwatch --output mail --format html --mailto root --range yesterday --service all

#!/bin/bash

#Check if removed-but-not-purged
test -x /usr/share/logwatch/scripts/logwatch.pl || exit 0

#execute
/usr/sbin/logwatch --output mail --format html --mailto root --range yesterday --service all

#Note: It's possible to force the recipient in above command
#Just pass --mailto address@a.com instead of --output mail

For the lazy:

sudo sed -i -r -e "s,^($(sudo which logwatch).*?),# \1         # commented by $(whoami) on $(date +"%Y-%m-%d @ %H:%M:%S")\n$(sudo which logwatch) --output mail --format html --mailto root --range yesterday --service all         # added by $(whoami) on $(date +"%Y-%m-%d @ %H:%M:%S")," /etc/cron.daily/00logwatch

You can test the cron job by executing it:

sudo /etc/cron.daily/00logwatch

Note: If logwatch fails to deliver mail due to the e-mail having long lines please check https://blog.dhampir.no/content/exim4-line-length-in-debian-stretch-mail-delivery-failed-returning-message-to-sender as documented in issue #29. If you you followed Gmail and Exim4 As MTA With Implicit TLS then we already took care of this in step #7.

ss - Seeing Ports Your Server Is Listening On

Why

Ports are how applications, services, and processes communicate with each other -- either locally within your server or with other devices on the network. When you have an application or service (like SSH or Apache) running on your server, they listen for requests on specific ports.

Obviously we don't want your server listening on ports we don't know about. We'll use ss to see all the ports that services are listening on. This will help us track down and stop rogue, potentially dangerous, services.

Goals

• find out non-localhost what ports are open and listening for connections

References

• https://www.reddit.com/r/linux/comments/arx7st/howtosecurealinuxserver_an_evolving_howto_guide/egrib6o/
• https://www.reddit.com/r/linux/comments/arx7st/howtosecurealinuxserver_an_evolving_howto_guide/egs1rev/
• https://www.tecmint.com/find-open-ports-in-linux/
• man ss

Steps

To see the all the ports listening for traffic:

sudo ss -lntup

Netid  State      Recv-Q Send-Q     Local Address:Port     Peer Address:Port
udp    UNCONN     0      0                      *:68                  *:*        users:(("dhclient",pid=389,fd=6))
tcp    LISTEN     0      128                    *:22                  *:*        users:(("sshd",pid=4390,fd=3))
tcp    LISTEN     0      128                   :::22                 :::*        users:(("sshd",pid=4390,fd=4))

Switch Explanations:

• l = display listening sockets
• n = do now try to resolve service names
• t = display TCP sockets
• u = display UDP sockets
• p = show process information

If you see anything suspicious, like a port you're not aware of or a process you don't know, investigate and remediate as necessary.

Lynis - Linux Security Auditing

Why

From https://cisofy.com/lynis/:

Lynis is a battle-tested security tool for systems running Linux, macOS, or Unix-based operating system. It performs an extensive health scan of your systems to support system hardening and compliance testing.

Goals

• Lynis installed

Notes

• CISOFY offers packages for many distributions. Check https://packages.cisofy.com/ for distribution specific installation instructions.

References

• https://cisofy.com/documentation/lynis/get-started/
• https://packages.cisofy.com/community/#debian-ubuntu
• https://thelinuxcode.com/audit-lynis-ubuntu-server/
• https://www.vultr.com/docs/install-lynis-on-debian-8

Steps

Install lynis. https://cisofy.com/lynis/#installation has detailed instructions on how to install it for your distribution.

On Debian based systems, using CISOFY's community software repository:

sudo apt install apt-transport-https ca-certificates host
sudo wget -O - https://packages.cisofy.com/keys/cisofy-software-public.key | sudo apt-key add -
sudo echo "deb https://packages.cisofy.com/community/lynis/deb/ stable main" | sudo tee /etc/apt/sources.list.d/cisofy-lynis.list
sudo apt update
sudo apt install lynis host

Update it:

sudo lynis update info

Run a security audit:

sudo lynis audit system

This will scan your server, report its audit findings, and at the end it will give you suggestions. Spend some time going through the output and address gaps as necessary.

OSSEC - Host Intrusion Detection

Why

From https://github.com/ossec/ossec-hids

OSSEC is a full platform to monitor and control your systems. It mixes together all the aspects of HIDS (host-based intrusion detection), log monitoring and SIM/SIEM together in a simple, powerful and open source solution.

Goals

• OSSEC-HIDS installed

References

• https://www.ossec.net/docs/

Steps

Install OSSEC-HIDS from sources

sudo apt install libz-dev libssl-dev libpcre2-dev build-essential
wget https://github.com/ossec/ossec-hids/archive/3.6.0.tar.gz
tar xzf 3.6.0.tar.gz
cd ossec-hids-3.6.0/
sudo ./install.sh

Useful commands:

Agent information

 sudo /var/ossec/bin/agent_control -i <AGENT_ID>

AGENT_ID by default is 000, to be sure the command sudo /var/ossec/bin/agent_control -l can be used.

Run integrity/rootkit checking

OSSEC by default run rootkit check each 2 hours.

 sudo /var/ossec/bin/agent_control -u <AGENT_ID> -r 

Alerts

• All:

tail -f /var/ossec/logs/alerts/alerts.log

• Integrity check:

sudo cat /var/ossec/logs/alerts/alerts.log | grep -A4  -i integrity

• Rootkit check:

 sudo cat /var/ossec/logs/alerts/alerts.log | grep -A4  "rootcheck,"

The Danger Zone

Proceed At Your Own Risk

This sections cover things that are high risk because there is a possibility they can make your system unusable, or are considered unnecessary by many because the risks outweigh any rewards.

!! PROCEED AT YOUR OWN RISK !!

!! PROCEED AT YOUR OWN RISK !!

Linux Kernel sysctl Hardening

!! PROCEED AT YOUR OWN RISK !!

Why

The kernel is the brains of a Linux system. Securing it just makes sense.

Why Not

Changing kernel settings with sysctl is risky and could break your server. If you don't know what you are doing, don't have the time to debug issues, or just don't want to take the risks, I would advise from not following these steps.

Disclaimer

I am not as knowledgeable about hardening/securing a Linux kernel as I'd like. As much as I hate to admit it, I do not know what all of these settings do. My understanding is that most of them are general kernel hardening and performance, and the others are to protect against spoofing and DOS attacks.

In fact, since I am not 100% sure exactly what each setting does, I took recommended settings from numerous sites (all linked in the references below) and combined them to figure out what should be set. I figure if multiple reputable sites mention the same setting, it's probably safe.

If you have a better understanding of what these settings do, or have any other feedback/advice on them, please let me know.

I won't provide For the lazy code in this section.

Notes

• Documentation on all the sysctl settings/keys is severely lacking. The documentation I can find seems to reference the 2.2 version kernel. I could not find anything newer. If you know where I can, please let me know.
• The reference sites listed below have more comments on what each setting does.

References

• https://github.com/torvalds/linux/tree/master/Documentation
• https://www.cyberciti.biz/faq/linux-kernel-etcsysctl-conf-security-hardening/
• https://geektnt.com/sysctl-conf-hardening.html
• https://linoxide.com/how-tos/linux-server-protection/
• https://github.com/klaver/sysctl/blob/master/sysctl.conf
• https://cloudpro.zone/index.php/2018/01/30/debian-9-3-server-setup-guide-part-5/

Steps

The sysctl settings can be found in the linux-kernel-sysctl-hardening.md file in this repo.

Before you make a kernel sysctl change permanent, you can test it with the sysctl command:

sudo sysctl -w [key=value]

Example:

sudo sysctl -w kernel.ctrl-alt-del=0

Note: There are no spaces in key=value, including before and after the space.

Once you have tested a setting, and made sure it works without breaking your server, you can make it permanent by adding the values to /etc/sysctl.conf. For example:

$ sudo cat /etc/sysctl.conf
kernel.ctrl-alt-del = 0
fs.file-max = 65535
...
kernel.sysrq = 0

After updating the file you can reload the settings or reboot. To reload:

sudo sysctl -p

Note: If sysctl has trouble writing any settings then sysctl -w or sysctl -p will write an error to stderr. You can use this to quickly find invalid settings in your /etc/sysctl.conf file:

sudo sysctl -p >/dev/null

Password Protect GRUB

!! PROCEED AT YOUR OWN RISK !!

Why

If a bad actor has physical access to your server, they could use GRUB to gain unauthorized access to your system.

Why Not

If you forget the password, you'll have to go through some work to recover the password.

Goals

• auto boot the default Debian install and require a password for anything else

Notes

• This will only protect GRUB and anything behind it like your operating systems. Check your motherboard's documentation for password protecting your BIOS to prevent a bad actor from circumventing GRUB.

References

• https://selivan.github.io/2017/12/21/grub2-password-for-all-but-default-menu-entries.html
• https://help.ubuntu.com/community/Grub2/Passwords
• https://computingforgeeks.com/how-to-protect-grub-with-password-on-debian-ubuntu-and-kali-linux/
• man grub
• man grub-mkpasswd-pbkdf2

Steps

Create a Password-Based Key Derivation Function 2 (PBKDF2) hash of your password:

grub-mkpasswd-pbkdf2 -c 100000

The below output is from using password as the password:

Enter password:
Reenter password:
PBKDF2 hash of your password is grub.pbkdf2.sha512.100000.2812C233DFC899EFC3D5991D8CA74068C99D6D786A54F603E9A1EFE7BAEDDB6AA89672F92589FAF98DB9364143E7A1156C9936328971A02A483A84C3D028C4FF.C255442F9C98E1F3C500C373FE195DCF16C56EEBDC55ABDD332DD36A92865FA8FC4C90433757D743776AB186BD3AE5580F63EF445472CC1D151FA03906D08A6D

grub-mkpasswd-pbkdf2 -c 100000

Copy everything after PBKDF2 hash of your password is , starting from and including grub.pbkdf2.sha512... to the end. You'll need this in the next step.

The update-grub program uses scripts to generate configuration files it will use for GRUB's settings. Create the file /etc/grub.d/01_password and add the below code after replacing [hash] with the hash you copied from the first step. This tells update-grub to use this username and password for GRUB.

#!/bin/sh
set -e

cat << EOF
set superusers="grub"
password_pbkdf2 grub [hash]
EOF

For example:

#!/bin/sh
set -e

cat << EOF
set superusers="grub"
password_pbkdf2 grub grub.pbkdf2.sha512.100000.2812C233DFC899EFC3D5991D8CA74068C99D6D786A54F603E9A1EFE7BAEDDB6AA89672F92589FAF98DB9364143E7A1156C9936328971A02A483A84C3D028C4FF.C255442F9C98E1F3C500C373FE195DCF16C56EEBDC55ABDD332DD36A92865FA8FC4C90433757D743776AB186BD3AE5580F63EF445472CC1D151FA03906D08A6D
EOF

Set the file's execute bit so update-grub includes it when it updates GRUB's configuration:

sudo chmod a+x /etc/grub.d/01_password

Make a backup of GRUB's configuration file /etc/grub.d/10_linux that we'll be modifying and unset the execute bit so update-grub doesn't try to run it:

sudo cp --archive /etc/grub.d/10_linux /etc/grub.d/10_linux-COPY-$(date +"%Y%m%d%H%M%S")
sudo chmod a-x /etc/grub.d/10_linux.*

To make the default Debian install unrestricted (without the password) while keeping everything else restricted (with the password) modify /etc/grub.d/10_linux and add --unrestricted to the CLASS variable.

For the lazy:

sudo sed -i -r -e "/^CLASS=/ a CLASS=\"\${CLASS} --unrestricted\"         # added by $(whoami) on $(date +"%Y-%m-%d @ %H:%M:%S")" /etc/grub.d/10_linux

Update GRUB with update-grub:

sudo update-grub

 

Disable Root Login

!! PROCEED AT YOUR OWN RISK !!

Why

If you have sudo configured properly, then the root account will mostly never need to log in directly -- either at the terminal or remotely.

Why Not

Be warned, this can cause issues with some configurations!

If your installation uses sulogin (like Debian) to drop to a root console during boot failures, then locking the root account will prevent sulogin from opening the root shell and you will get this error:

Cannot open access to console, the root account is locked.

See sulogin(8) man page for more details.

Press Enter to continue.

To work around this, you can use the --force option for sulogin. Some distributions already include this, or some other, workaround.

An alternative to locking the root acount is set a long/complicated root password and store it in a secured, non digital format. That way you have it when/if you need it.

Goals

• locked root account that nobody can use to log in as root

Notes

• Some distributions disable root login by default (e.g. Ubuntu) so you may not need to do this step. Check with your distribution's documentation.

References

• https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=806852
• https://github.com/systemd/systemd/issues/7115
• https://github.com/karelzak/util-linux/commit/7ff1162e67164cb4ece19dd809c26272461aa254
• https://github.com/systemd/systemd/issues/11596
• https://www.reddit.com/r/selfhosted/comments/aoxd4l/new_guide_created_by_me_how_to_secure_a_linux/eg4rkfi/
• man systemd

Steps

Lock the root account:

sudo passwd -l root

Change Default umask

!! PROCEED AT YOUR OWN RISK !!

Why

umask controls the default permissions of files/folders when they are created. Insecure file/folder permissions give other accounts potentially unauthorized access to your data. This may include the ability to make configuration changes.

• For non-root accounts, there is no need for other accounts to get any access to the account's files/folders by default.
• For the root account, there is no need for the file/folder primary group or other accounts to have any access to root's files/folders by default.

When and if other accounts need access to a file/folder, you want to explicitly grant it using a combination of file/folder permissions and primary group.

Why Not

Changing the default umask can create unexpected problems. For example, if you set umask to 0077 for root, then non-root accounts will not have access to application configuration files/folders in /etc/ which could break applications that do not run with root privileges.

How It Works

In order to explain how umask works I'd have to explain how Linux file/folder permissions work. As that is a rather complicated question, I will defer you to the references below for further reading.

Goals

• set default umask for non-root accounts to 0027
• set default umask for the root account to 0077

Notes

• umask is a Bash built-in which means a user can change their own umask setting.

References

• https://www.linuxnix.com/umask-define-linuxunix/
• https://serverfault.com/questions/818783/which-umask-is-more-secure-in-linux-022-or-027
• https://www.cyberciti.biz/tips/understanding-linux-unix-umask-value-usage.html
• man umask

Steps

Make a backup of files we'll be editing:

sudo cp --archive /etc/profile /etc/profile-COPY-$(date +"%Y%m%d%H%M%S")
sudo cp --archive /etc/bash.bashrc /etc/bash.bashrc-COPY-$(date +"%Y%m%d%H%M%S")
sudo cp --archive /etc/login.defs /etc/login.defs-COPY-$(date +"%Y%m%d%H%M%S")
sudo cp --archive /root/.bashrc /root/.bashrc-COPY-$(date +"%Y%m%d%H%M%S")

Set default umask for non-root accounts to 0027 by adding this line to /etc/profile and /etc/bash.bashrc:

umask 0027

For the lazy:

echo -e "\numask 0027         # added by $(whoami) on $(date +"%Y-%m-%d @ %H:%M:%S")" | sudo tee -a /etc/profile /etc/bash.bashrc

We also need to add this line to /etc/login.defs:

UMASK 0027

For the lazy:

echo -e "\nUMASK 0027         # added by $(whoami) on $(date +"%Y-%m-%d @ %H:%M:%S")" | sudo tee -a /etc/login.defs

Set default umask for the root account to 0077 by adding this line to /root/.bashrc:

umask 0077

For the lazy:

echo -e "\numask 0077         # added by $(whoami) on $(date +"%Y-%m-%d @ %H:%M:%S")" | sudo tee -a /root/.bashrc

 

Orphaned Software

!! PROCEED AT YOUR OWN RISK !!

Why

As you use your system, and you install and uninstall software, you'll eventually end up with orphaned, or unused software/packages/libraries. You don't need to remove them, but if you don't need them, why keep them? When security is a priority, anything not explicitly needed is a potential security threat. You want to keep your server as trimmed and lean as possible.

Notes

• Each distribution manages software/packages/libraries differently so how you find and remove orphaned packages will be different. So far I only have steps for Debian based systems.

Debian Based Systems

On Debian based systems, you can use deborphan to find orphaned packages.

Why Not

Keep in mind, deborphan finds packages that have no package dependencies. That does not mean they are not used. You could very well have a package you use every day that has no dependencies that you wouldn't want to remove. And, if deborphan gets anything wrong, then removing critical packages may break your system.

Steps

Install deborphan.

sudo apt install deborphan

Run deborphan as root to see a list of orphaned packages:

sudo deborphan

libxapian30
libpipeline1

Assuming you want to remove all of the packages deborphan finds, you can pass it's output to apt to remove them:

sudo apt --autoremove purge $(deborphan)

 

The Miscellaneous

The Simple way with MSMTP

(#msmtp-alternative)

Why

Well I will SIMPLIFY this method, to only output email using google mail account (and others). True Simple! :)

``` bash
#!/bin/bash
###### PLEASE .... EDIT IT...
USRMAIL="usernameemail"
DOMPROV="gmail.com"
PWDEMAIL="passwordStrong"  ## ATTENTION DONT USE Special Chars.. like as SPACE # and some others not all. Feel free to test ;)
MAILPROV="smtp.google.com:583"
MYMAIL="$USRMAIL@$DOMPROV"
USERLOC="root"
#######
apt install -y msmtp
    ln -s /usr/bin/msmtp /usr/sbin/sendmail
#wget http://www.cacert.org/revoke.crl -O /etc/ssl/certs/revoke.crl
#chmod 644 /etc/ssl/certs/revoke.crl
touch /root/.msmtprc
cat <<EOF> .msmtprc
defaults
account gmail
host $MAILPROV
port $MAILPORT
#proxy_host 127.0.0.1
#proxy_port 9001
from $MYEMAIL
timeout off 
protocol smtp
#auto_from [(on|off)]
#from envelope_from
#maildomain [domain]
auth on
user $USRMAIL
passwordeval "gpg -q --for-your-eyes-only --no-tty -d /root/msmtp-mail.gpg"
#passwordeval "gpg --quiet --for-your-eyes-only --no-tty --decrypt /root/msmtp-mail.gpg"
tls on
tls_starttls on
tls_trust_file /etc/ssl/certs/ca-certificates.crt
#tls_crl_file /etc/ssl/certs/revoke.crl
#tls_fingerprint [fingerprint]
#tls_key_file [file]
#tls_cert_file [file]
tls_certcheck on
tls_force_sslv3 on
tls_min_dh_prime_bits 512
#tls_priorities [priorities]
#dsn_notify (off|condition)
#dsn_return (off|amount)
#domain argument
#keepbcc off
logfile /var/log/mail.log
syslog on
account default : gmail
EOF
chmod 0400 /root/.msmtprc

   ## In testing .. auto command
# echo -e "1\n4096\n\ny\n$MYUSRMAIL\n$MYEMAIL\nmy key\nO\n$PWDMAIL\n$PWDMAIL\n" | gpg --full-generate-key 
##
gpg --full-generate-key
gpg --output revoke.asc --gen-revoke $MYEMAIL
echo -e "$PWDEMAIL\n" | gpg -e -o /root/msmtp-mail.gpg --recipient $MYEMAIL
echo "export GPG_TTY=\$(tty)" >> .baschrc    
chmod 400 msmtp-mail.gpg

echo "Hello there" | msmtp --debug $MYEMAIL
echo"######################
## MSMTP Configured ##
######################"
```

DONE!! ;)

Gmail and Exim4 As MTA With Implicit TLS

Why

Unless you're planning on setting up your own mail server, you'll need a way to send e-mails from your server. This will be important for system alerts/messages.

You can use any Gmail account. I recommend you create one specific for this server. That way if your server is compromised, the bad-actor won't have any passwords for your primary account. Granted, if you have 2FA/MFA enabled and you use an app password, there isn't much a bad-actor can do with just the app password, but why take the risk?

There are many guides on-line that cover how to configure Gmail as MTA using STARTTLS including a previous version of this guide. With STARTTLS, an initial unencrypted connection is made and then upgraded to an encrypted TLS or SSL connection. Instead, with the approach outlined below, an encrypted TLS connection is made from the start.

Also, as discussed in issue #29 and here, exim4 will fail for messages with long lines. We'll fix this in this section too.

Goals

• mail configured to send e-mails from your server using Gmail
• long line support for exim4

References

• Thanks to remyabel for figuring out how to get this to work with TLS as documented in issue #24 and pull request #26.
• https://wiki.debian.org/Exim
• https://wiki.debian.org/GmailAndExim4
• https://www.exim.org/exim-html-current/doc/html/spec_html/ch-encrypted_smtp_connections_using_tlsssl.html
• https://php.quicoto.com/setup-exim4-to-use-gmail-in-ubuntu/
• https://www.fastmail.com/help/technical/ssltlsstarttls.html
• exim4 fails for messages with long lines - issue #29 and https://blog.dhampir.no/content/exim4-line-length-in-debian-stretch-mail-delivery-failed-returning-message-to-sender

Steps

Install exim4. You will also need openssl and ca-certificates.

On Debian based systems:

sudo apt install exim4 openssl ca-certificates

Configure exim4:

For Debian based systems:

sudo dpkg-reconfigure exim4-config

You'll be prompted with some questions:

Prompt	Answer
General type of mail configuration	mail sent by smarthost; no local mail
System mail name	localhost
IP-addresses to listen on for incoming SMTP connections	127.0.0.1; ::1
Other destinations for which mail is accepted	(default)
Visible domain name for local users	localhost
IP address or host name of the outgoing smarthost	smtp.gmail.com::465
Keep number of DNS-queries minimal (Dial-on-Demand)?	No
Split configuration into small files?	No

Make a backup of /etc/exim4/passwd.client:

sudo cp --archive /etc/exim4/passwd.client /etc/exim4/passwd.client-COPY-$(date +"%Y%m%d%H%M%S")

Add a line like this to /etc/exim4/passwd.client

Notes:

• Replace yourAccount@gmail.com and yourPassword with your details. If you have 2FA/MFA enabled on your Gmail then you'll need to create and use an app password here.
• Always check host smtp.gmail.com for the most up-to-date domains to list.

smtp.gmail.com:yourAccount@gmail.com:yourPassword
*.google.com:yourAccount@gmail.com:yourPassword

This file has your Gmail password so we need to lock it down:

sudo chown root:Debian-exim /etc/exim4/passwd.client
sudo chmod 640 /etc/exim4/passwd.client

The next step is to create an TLS certificate that exim4 will use to make the encrypted connection to smtp.gmail.com. You can use your own certificate, like one from Let's Encrypt, or create one yourself using openssl. We will use a script that comes with exim4 that calls openssl to make our certificate:

sudo bash /usr/share/doc/exim4-base/examples/exim-gencert

[*] Creating a self signed SSL certificate for Exim!
    This may be sufficient to establish encrypted connections but for
    secure identification you need to buy a real certificate!

    Please enter the hostname of your MTA at the Common Name (CN) prompt!

Generating a RSA private key
..........................................+++++
................................................+++++
writing new private key to '/etc/exim4/exim.key'
-----
You are about to be asked to enter information that will be incorporated
into your certificate request.
What you are about to enter is what is called a Distinguished Name or a DN.
There are quite a few fields but you can leave some blank
For some fields there will be a default value,
If you enter '.', the field will be left blank.
-----
Country Code (2 letters) [US]:[redacted]
State or Province Name (full name) []:[redacted]
Locality Name (eg, city) []:[redacted]
Organization Name (eg, company; recommended) []:[redacted]
Organizational Unit Name (eg, section) []:[redacted]
Server name (eg. ssl.domain.tld; required!!!) []:localhost
Email Address []:[redacted]
[*] Done generating self signed certificates for exim!
    Refer to the documentation and example configuration files
    over at /usr/share/doc/exim4-base/ for an idea on how to enable TLS
    support in your mail transfer agent.

Instruct exim4 to use TLS and port 465, and fix exim4's long lines issue, by creating the file /etc/exim4/exim4.conf.localmacros and adding:

MAIN_TLS_ENABLE = 1
REMOTE_SMTP_SMARTHOST_HOSTS_REQUIRE_TLS = *
TLS_ON_CONNECT_PORTS = 465
REQUIRE_PROTOCOL = smtps
IGNORE_SMTP_LINE_LENGTH_LIMIT = true

For the lazy:

cat << EOF | sudo tee /etc/exim4/exim4.conf.localmacros
MAIN_TLS_ENABLE = 1
REMOTE_SMTP_SMARTHOST_HOSTS_REQUIRE_TLS = *
TLS_ON_CONNECT_PORTS = 465
REQUIRE_PROTOCOL = smtps
IGNORE_SMTP_LINE_LENGTH_LIMIT = true
EOF

Make a backup of exim4's configuration file /etc/exim4/exim4.conf.template:

sudo cp --archive /etc/exim4/exim4.conf.template /etc/exim4/exim4.conf.template-COPY-$(date +"%Y%m%d%H%M%S")

Add the below to /etc/exim4/exim4.conf.template after the .ifdef REMOTE_SMTP_SMARTHOST_HOSTS_REQUIRE_TLS ... .endif block:

.ifdef REQUIRE_PROTOCOL
  protocol = REQUIRE_PROTOCOL
.endif

.ifdef REMOTE_SMTP_SMARTHOST_HOSTS_REQUIRE_TLS
  hosts_require_tls = REMOTE_SMTP_SMARTHOST_HOSTS_REQUIRE_TLS
.endif
.ifdef REQUIRE_PROTOCOL
    protocol = REQUIRE_PROTOCOL
.endif
.ifdef REMOTE_SMTP_HEADERS_REWRITE
  headers_rewrite = REMOTE_SMTP_HEADERS_REWRITE
.endif

For the lazy:

sudo sed -i -r -e '/^.ifdef REMOTE_SMTP_SMARTHOST_HOSTS_REQUIRE_TLS$/I { :a; n; /^.endif$/!ba; a\# added by '"$(whoami) on $(date +"%Y-%m-%d @ %H:%M:%S")"'\n.ifdef REQUIRE_PROTOCOL\n    protocol = REQUIRE_PROTOCOL\n.endif\n# end add' -e '}' /etc/exim4/exim4.conf.template

.ifdef REQUIRE_PROTOCOL
  protocol = REQUIRE_PROTOCOL
.endif

Add the below to /etc/exim4/exim4.conf.template inside the .ifdef MAIN_TLS_ENABLE block:

.ifdef MAIN_TLS_ENABLE
.ifdef TLS_ON_CONNECT_PORTS
    tls_on_connect_ports = TLS_ON_CONNECT_PORTS
.endif

For the lazy:

sudo sed -i -r -e "/\.ifdef MAIN_TLS_ENABLE/ a # added by $(whoami) on $(date +"%Y-%m-%d @ %H:%M:%S")\n.ifdef TLS_ON_CONNECT_PORTS\n    tls_on_connect_ports = TLS_ON_CONNECT_PORTS\n.endif\n# end add" /etc/exim4/exim4.conf.template

.ifdef TLS_ON_CONNECT_PORTS
  tls_on_connect_ports = TLS_ON_CONNECT_PORTS
.endif

Update exim4 configuration to use TLS and then restart the service:

sudo update-exim4.conf
sudo service exim4 restart

If you're using UFW, you'll need to allow outbound traffic on 465. To do this we'll create a custom UFW application profile and then enable it. Create the file /etc/ufw/applications.d/smtptls, add this, then run ufw allow out smtptls comment 'open TLS port 465 for use with SMPT to send e-mails':

For the lazy:

cat << EOF | sudo tee /etc/ufw/applications.d/smtptls
[SMTPTLS]
title=SMTP through TLS
description=This opens up the TLS port 465 for use with SMPT to send e-mails.
ports=465/tcp
EOF

sudo ufw allow out smtptls comment 'open TLS port 465 for use with SMPT to send e-mails'

[SMTPTLS]
title=SMTP through TLS
description=This opens up the TLS port 465 for use with SMPT to send e-mails.
ports=465/tcp

Add some mail aliases so we can send e-mails to local accounts by adding lines like this to /etc/aliases:

You'll need to add all the local accounts that exist on your server.

user1: user1@gmail.com
user2: user2@gmail.com
...

Test your setup:

echo "test" | mail -s "Test" email@gmail.com
sudo tail /var/log/exim4/mainlog

Separate iptables Log File

Why

There will come a time when you'll need to look through your iptables logs. Having all the iptables logs go to their own file will make it a lot easier to find what you're looking for.

References

• https://blog.shadypixel.com/log-iptables-messages-to-a-separate-file-with-rsyslog/
• https://gist.github.com/netson/c45b2dc4e835761fbccc
• https://www.rsyslog.com/doc/v8-stable/configuration/actions.html

Steps

The first step is by telling your firewall to prefix all log entries with some unique string. If you're using iptables directly, you would do something like --log-prefix "[IPTABLES] " for all the rules. We took care of this in step step 4 of installing psad.

After you've added a prefix to the firewall logs, we need to tell rsyslog to send those lines to its own file. Do this by creating the file /etc/rsyslog.d/10-iptables.conf and adding this:

:msg, contains, "[IPTABLES] " /var/log/iptables.log
& stop

If you're expecting a lot if data being logged by your firewall, prefix the filename with a - "to omit syncing the file after every logging". For example:

:msg, contains, "[IPTABLES] " -/var/log/iptables.log
& stop

Note: Remember to change the prefix to whatever you use.

For the lazy:

cat << EOF | sudo tee /etc/rsyslog.d/10-iptables.conf
:msg, contains, "[IPTABLES] " /var/log/iptables.log
& stop
EOF

:msg, contains, "[IPTABLES] " -/var/log/iptables.log
& stop

:msg, contains, "[IPTABLES] " /var/log/iptables.log
& stop

Since we're logging firewall messages to a different file, we need to tell psad where the new file is. Edit /etc/psad/psad.conf and set IPT_SYSLOG_FILE to the path of the log file. For example:

Note: Remember to change the prefix to whatever you use.

For the lazy:

sudo sed -i -r -e "s/^(IPT_SYSLOG_FILE\s+)([^;]+)(;)$/# \1\2\3       # commented by $(whoami) on $(date +"%Y-%m-%d @ %H:%M:%S")\n\1\/var\/log\/iptables.log\3       # added by $(whoami) on $(date +"%Y-%m-%d @ %H:%M:%S")/" /etc/psad/psad.conf 

IPT_SYSLOG_FILE /var/log/iptables.log;

Restart psad and rsyslog to activate the changes (or reboot):

sudo psad -R
sudo psad --sig-update
sudo psad -H
sudo service rsyslog restart

The last thing we have to do is tell logrotate to rotate the new log file so it doesn't get to big and fill up our disk. Create the file /etc/logrotate.d/iptables and add this:

For the lazy:

cat << EOF | sudo tee /etc/logrotate.d/iptables
/var/log/iptables.log
{
    rotate 7
    daily
    missingok
    notifempty
    delaycompress
    compress
    postrotate
        invoke-rc.d rsyslog rotate > /dev/null
    endscript
}
EOF

/var/log/iptables.log
{
    rotate 7
    daily
    missingok
    notifempty
    delaycompress
    compress
    postrotate
        invoke-rc.d rsyslog rotate > /dev/null
    endscript
}

(Table of Contents)

Left Over

Contacting Me

For any questions, comments, concerns, feedback, or issues, submit a new issue.

(Table of Contents)

Helpful Links

• https://github.com/pratiktri/server_init_harden - Bash script that automates few of the tasks that you need to perform on a new Linux server to give it basic amount security.

(Table of Contents)

Acknowledgments

• https://www.reddit.com/r/linuxquestions/comments/aopzl7/new_guide_created_by_me_how_to_secure_a_linux/
• https://www.reddit.com/r/selfhosted/comments/aoxd4l/new_guide_created_by_me_how_to_secure_a_linux/
• https://news.ycombinator.com/item?id=19177435#19178618
• https://www.reddit.com/r/linuxadmin/comments/arx7xo/howtosecurealinuxserver_an_evolving_howto_guide/
• https://www.reddit.com/r/linux/comments/arx7st/howtosecurealinuxserver_an_evolving_howto_guide/

 

Download Details: 
Author: imthenachoman
Source Code: https://github.com/imthenachoman/How-To-Secure-A-Linux-Server 
License: CC-BY-SA-4.0 License
#linux #security 

I Wish I Had Read These 29 Things Before I Started Programming

Programming is not an easy career. With many people graduating each year from top computer science programs in the country, it’s one of the most competitive careers anyone can embark on. At the same time, a programming career is exciting. With the advancement of technology, every day, there are innovations in the industry. Programming becomes a passionate endeavor for those who love it.

When I started as a programmer years ago, I wish someone sat me down and told me everything on this list. This list can save any new programmer a lot of headaches and energy. This list can be the one you refer to as your programming career progresses. Even if some of these points might not be relevant for you right now, one day you will see the wisdom in them.

As a programmer, you are at the cusp of greatness.

You just have to venture on with a little bit of knowledge about your path.

1. You Don’t Need a Degree to Program, but You Do Need the Knowledge

I worked with many programmers who didn’t graduate with a computer science master’s degree or an undergraduate degree in computer science. Programming is one of the few careers you can have that doesn’t depend on a degree. However, programming is a knowledge-intensive career. You have to read those ten essential books if you’re going to start a career in programming. These ten books will cover the essential concepts of computer science as well as how to work on project teams. Setting a firm foundation for your technical skills, with a solid understanding of the basic concepts, on top of writing functional code, will enable you to ace technical interviews and communicate with your co-workers.

2. Programming Takes Creativity on Top of Problem-Solving Skills

Most people have the preconception that programming is all about analytical and problem-solving skills. That is partially true. Programming also involves a lot of creativity. Often, there are many ways to write a given piece of code. The creativity comes when you devise ways to code most simply and effectively.

3. You Can’t Learn Everything There Is to Learn. The Trick Is to Learn a Few Things Very Well

There are hundreds of programming languages out there. There are areas of programming that pave the way for particular career paths: web developer, front-end developer, back-end developer, software engineer, database developer, etc. Decide what kind of developer you want to be, then learn all the technologies and skillsets needed for that particular position.

4. You Don’t Need to Be a Robot. It’s Better If You Are Human

Remember you are a human first and a programmer second. It’s easy to get lost in your code when you first start to program. There are days when I don’t leave my computer until I’ve completed all the milestones of my project. But you are a human being; you need to laugh, cry, de-stress and talk to people. By managing your life to maximize fun and excitement outside of work, you will bring more creativity into your work as a programmer.

5. Programming Is All About Applying Knowledge. It’s Not About Memorization

Unlike research, where you are inventing and creating new areas of knowledge, programming is all about applying existing knowledge. Books, research papers, online articles, and learning videos become resources that you will use often. There’s no need to memorize anything. You can always reach for a resource to find the answer. Memorization comes automatically and naturally as you work on more projects.

6. You Will Deal With Imposter Syndrome Every Day

Programming is the one career all the “smart” people seem to gravitate towards. Unless you are a genius, you will, like I do, experience imposter syndrome every day. When you experience it every day, you tend to figure out a way to deal with it. For me, I’ve always used it as motivation to learn new things. I’ve learned to put it into perspective and just be content at improving a little bit each day.

7. You Have to Have a Life Outside of Being a Programmer. Otherwise, You’ll Just Be Addicted to Programming

There will be times when you are a hermit at home. However, to be a happy programmer, you have to proactively seek a life outside your computer screen. Often the success of your career depends on the people you meet. Networking is essential when you are a programmer. Having a personality outside of being a programmer is essential to keep yourself from being addicted to programming. When you can enjoy your passions without being compelled to do it, your best work comes out.

8. You’ll Learn Programming Faster If You Pair Program With Someone

At the beginning of your career, you’ll be tempted to close your door to the world and read those ten books on programming to build your computer science foundations. Guess what? You learn much faster if you find a buddy. I’ve gone through programming books in half the time working on a project with a buddy. When you pair program with someone, all your programming “warts” come out. Your code will be critiqued. You will learn to write efficient code because someone else is watching. You will want to find out the best way to do things because your buddy is learning too. When you work as a programmer, someone’s always reviewing your code. You are never programming alone. It’s time to get used to that.

9. You Don’t Need to Be Good at Math and Science

In the technology industry, you will meet all kinds of superstar programmers who found the logical thinking aspect of programming appealing after a lifetime of liberal arts education. There are plenty of painters and writers who make a living programming while pursuing art on the side. All you need to be a good programmer is persistence. Programming is hard work. But once you have that, anyone can go through programming books and pick up the basics. There are plenty of people who pick up math after working in the industry for a while. Eventually, these people can even understand complex algorithms and implement them without any kind of formal math education.

10. You Need to Be an All-Star “Learner”

A programmer is a master learner. You might not start out being a master learner. But you will get there. Sometimes your workplace will ask you to pick up three programming languages in six months. That’s the state of technology innovation. As programmers, we learn every day. Learning is like breathing. If you are uncomfortable with learning every day, you will be forced to get used to that.

11. You Will Obsess About Finishing Your Projects

Coding addiction is a real thing. At some point in your programming career, you will experience all-night programming marathons. You won’t want to go to sleep until you’ve finished your milestones. You’ll forget to eat, drink, or even get up from your desk because your brain is processing so much information. That is okay. Once you are done, take a walk outside. Go on vacation.

12. You Will Spend All Day Looking for One Tiny Bug

Most of the time, on programming projects, many pieces are interdependent on one another. Often, you will find that you cannot move on unless you’ve fixed one tiny bug that’s been lurking in your system. As a programmer, you will stress about the entire project unless you find this bug. You will sit at your computer all day looking for it. You will dream about the code at night until you find it.

13. You Will Spend Most of Your Time Googling for Answers That No One Can Answer for You

If you program in a popular language, you’ll be able to find the answers to most of the problems you encounter online. However, there are exceptions. Sometimes, no one has encountered the problems you bumped into. In this case, referring to programming books and asking around on programming boards often will point you in the right direction.

14. You Will Read a Design Pattern Book

It doesn’t matter if you graduated from the best computer science program in the country. There comes a time in every programmer’s career that you will sit down and read Head First Design Patterns from cover to cover. It’s probably one of the most read books for a new programmer. So, what are you waiting for? Pick it up and read it from cover to cover.

15. You Will Learn to Obsess About the Exact Spelling

At some point in every programmer’s career, you will have written enough code in your favorite language to want to do things your way. This includes the exact spelling of naming conventions that you give to your variables, your classes, and even the tables in your databases. You will scrutinize this to no end. The last thing you want is some bug that crept up because you misspelled a name. Remember, it’s okay to obsess about things if you have a good reason for it. When you don’t have a good reason for it, it’s just repetitive behavior.

16. You Will Give Up

How many times have I given up? I can’t even count. Sometimes you just bump into problems you can’t solve. Sometimes it gets so difficult that you just want to quit. Sometimes work environments make you want to quit. Your passions depend on your persistence. This is when you are tested. Are you here to stay or are you going to go? I always came back. Sometimes, after a few years of not programming a single line, I always came back as a new person ready to tackle a project. This is when you know you love your work. It’s when it becomes a home, a springboard for your adventures.

17. You Will Restart

If you believe in higher powers, you will be able to relate to this. Each time, when I see people come back to programming, it’s never about the money. It’s always for the love of programming. When you see someone who enjoys programming like you used to, you are envious. You can’t let it go. Then, suddenly, you are back pursuing a project. You know in your core that you live and breathe code. This is when you know that you are a true programmer.

18. You Will Go Back to Some Form of School to Learn the “Correct” Way of Doing Things

Even the best programmers graduating from elite computer science master’s programs will continue their education at work. In fact, on the job training is one of the best perks of working for large technology companies. Companies will send you on “expensive” courses and seminars to train you in the latest technologies they want you to use. If by chance, you’re still not learning enough at work, you will reach out to the many online coding academies and youtube videos to sharpen your skillsets.

19. You Will Be Hired by Someone You Don’t Want to Work For

Even if you are a mediocre programmer, there will come a time when certain companies will need your skills. When they are interviewing you, try to remember that you are interviewing them too. Depending on the company’s culture, you might find yourself wanting to say “no” to a cushy package. As a programmer, you will work long hours. It’s almost critical to find a company culture that you can fit into. Happiness leads to better work. If your skills are in demand, other companies will knock on your door. Please do not settle unless it’s necessary.

20. You Will Flunk a Technical Interview

Technical interviews are no joke. Senior programmers often make up technical interview questions for fun. Often, these questions are extra difficult for a reason. If you flunk the technical interview, it’s not the end of the world. It certainly does not say anything about your programming abilities. It only tests your knowledge base. Try to look on the bright side. If your people skills shine, managers will remember you. If they like you and you are not a fit for this role, they might still call you for another position.

21. You Will Be Told That You Are Great

At times in your career, you will feel like you are a star. Managers who depend on you to complete their projects will tell you how great you are to motivate you. You will feel like you are on top of the world. Remember that they are appealing to your ego. Stay grounded. There are always new technologies to learn. There are always new programmers who are better than you.

22. You Will Be Told That You Don’t Know Anything

At times in your career, you will feel like you don’t know anything. Someone who is frustrated with the project will make it a point to tell you that you don’t know anything. Perhaps they do this to put you in your place. But, since you are reading this, you will take it in stride. Because you probably know a lot more than you think you do. Each day that passes, you will learn a little more than the day before. After a year, people will look up to you. Keep at it. After some time, you may even gain the respect of the person who told you that you don’t know anything.

23. You Will Want to Compete With Other Programmers Who You Admire

One of the most awesome aspects of programming is competition. I love programming with people who I admire. When you can write code that a programmer you admire deems worthy, you will feel like you just won the lottery. Competition in programming is always in good fun. It’s not about who’s the best. It’s more about learning from each other.

24. You Will Not Understand a Word That Your Coworkers Just Said

In the beginning, this may happen once a week or once a month. At your new programming job, you will not understand what your coworker just said. This could be for two reasons. For the life of you, you just can’t get your head around their accent. In this case, ask another coworker to translate. There’s no shame in not being able to understand someone’s speech. Chances are, it took other coworkers years to get used to the accent too. The other reason is that what your coworker just said went completely over your head. That is also okay. After all, your coworker is the expert. Ask your coworker to explain it all in picture form. You’re going to want to pull up a chair for this. Chances are, it might take a while.

25. You Will Feel Shame Looking at the Spaghetti Code You Wrote Last Year

This happens all the time. I was criticized for my Perl code when I started. It was well-documented code that’s designed well, too. But I wrote it in a language that was difficult to read. So, I wrote the spaghetti code. But, each year, no matter how hard I try, I still find some spaghetti code that I whipped up quickly to get a job done. That’s what programmers do. We fix things and we patch things up. There’s no shame in that. When you realize that it’s you who wrote it, just step back and fix it if you can.

26. You Will Take Shelter in Your Database Projects When You Are Too Sick to Look at Another Line of Code

This happens when you’re on a nice programming trek up the mountain. It’s been two months. You need a break. But you love the momentum so you keep going. Then you realize that SQL is fun. You can’t figure out why you can’t look at another line of code. But somehow, putting data into the database and getting it out is now a joyful event. You revel in the simplicity of a completely logical language.

27. You Will Both Love and Hate Hackathons

Hackathons are common these days. Programmers get into teams and compete with each other. In the process, it’s intense learning in a few hours. You will love the hackathons for the camaraderie. You will hate it for the carpal tunnel syndrome that you developed while typing at top speed. You will also hate it for the crowded rooms that you work in and the sensory overstimulation that you receive during the event.

28. You Will Think You Don’t Understand a Word of English While Reading Research Papers

Do you speak English? Well, most people will say yes. But, I guarantee you that you will read some research paper over and over again and realize that it’s way over your head. For me, most of the research papers on algorithms seemed like a giant forest before I learned the foundations of college math. Then, suddenly, it all seemed to make sense.

29. You Will Buy Headphones

At some point in your career, you will realize that any kind of noise impedes your senses when you’re intensely focused on your code. Having good headphones that will cancel out external noise will allow you to work in crowded rooms with focus. At some point, you will also find that music helps you to code. I found out early in my coding career that the rhythm in music helps me code fluidly. Even now, I reach for some music when I need to be productive.

You may also like: 7 Skills of Highly Effective Programmer for Developers.

In hindsight, I’m actually really happy that I was so naive in the beginning. Knowing so little back then gave me the motivation to think critically about everything I learned later on.

Now I get to spend time helping other people achieve their goals through code. What could be better than that? Share what you think.

Happy coding !

#Programming #Coding #Learn To Code #Development #Education

How to start an electric scooter facility/fleet in a university campus/IT park

Are you leading an organization that has a large campus, e.g., a large university? You are probably thinking of introducing an electric scooter/bicycle fleet on the campus, and why wouldn’t you?

Introducing micro-mobility in your campus with the help of such a fleet would help the people on the campus significantly. People would save money since they don’t need to use a car for a short distance. Your campus will see a drastic reduction in congestion, moreover, its carbon footprint will reduce.

Micro-mobility is relatively new though and you would need help. You would need to select an appropriate fleet of vehicles. The people on your campus would need to find electric scooters or electric bikes for commuting, and you need to provide a solution for this.

To be more specific, you need a short-term electric bike rental app. With such an app, you will be able to easily offer micro-mobility to the people on the campus. We at Devathon have built Autorent exactly for this.

What does Autorent do and how can it help you? How does it enable you to introduce micro-mobility on your campus? We explain these in this article, however, we will touch upon a few basics first.

Micro-mobility: What it is

You are probably thinking about micro-mobility relatively recently, aren’t you? A few relevant insights about it could help you to better appreciate its importance.

Micro-mobility is a new trend in transportation, and it uses vehicles that are considerably smaller than cars. Electric scooters (e-scooters) and electric bikes (e-bikes) are the most popular forms of micro-mobility, however, there are also e-unicycles and e-skateboards.

You might have already seen e-scooters, which are kick scooters that come with a motor. Thanks to its motor, an e-scooter can achieve a speed of up to 20 km/h. On the other hand, e-bikes are popular in China and Japan, and they come with a motor, and you can reach a speed of 40 km/h.

You obviously can’t use these vehicles for very long commutes, however, what if you need to travel a short distance? Even if you have a reasonable public transport facility in the city, it might not cover the route you need to take. Take the example of a large university campus. Such a campus is often at a considerable distance from the central business district of the city where it’s located. While public transport facilities may serve the central business district, they wouldn’t serve this large campus. Currently, many people drive their cars even for short distances.

As you know, that brings its own set of challenges. Vehicular traffic adds significantly to pollution, moreover, finding a parking spot can be hard in crowded urban districts.

Well, you can reduce your carbon footprint if you use an electric car. However, electric cars are still new, and many countries are still building the necessary infrastructure for them. Your large campus might not have the necessary infrastructure for them either. Presently, electric cars don’t represent a viable option in most geographies.

As a result, you need to buy and maintain a car even if your commute is short. In addition to dealing with parking problems, you need to spend significantly on your car.

All of these factors have combined to make people sit up and think seriously about cars. Many people are now seriously considering whether a car is really the best option even if they have to commute only a short distance.

This is where micro-mobility enters the picture. When you commute a short distance regularly, e-scooters or e-bikes are viable options. You limit your carbon footprints and you cut costs!

Businesses have seen this shift in thinking, and e-scooter companies like Lime and Bird have entered this field in a big way. They let you rent e-scooters by the minute. On the other hand, start-ups like Jump and Lyft have entered the e-bike market.

Think of your campus now! The people there might need to travel short distances within the campus, and e-scooters can really help them.

How micro-mobility can benefit you

What advantages can you get from micro-mobility? Let’s take a deeper look into this question.

Micro-mobility can offer several advantages to the people on your campus, e.g.:

• Affordability: Shared e-scooters are cheaper than other mass transportation options. Remember that the people on your campus will use them on a shared basis, and they will pay for their short commutes only. Well, depending on your operating model, you might even let them use shared e-scooters or e-bikes for free!
• Convenience: Users don’t need to worry about finding parking spots for shared e-scooters since these are small. They can easily travel from point A to point B on your campus with the help of these e-scooters.
• Environmentally sustainable: Shared e-scooters reduce the carbon footprint, moreover, they decongest the roads. Statistics from the pilot programs in cities like Portland and Denver showimpressive gains around this key aspect.
• Safety: This one’s obvious, isn’t it? When people on your campus use small e-scooters or e-bikes instead of cars, the problem of overspeeding will disappear. you will see fewer accidents.

#android app #autorent #ios app #mobile app development #app like bird #app like bounce #app like lime #autorent #bird scooter business model #bird scooter rental #bird scooter rental cost #bird scooter rental price #clone app like bird #clone app like bounce #clone app like lime #electric rental scooters #electric scooter company #electric scooter rental business #how do you start a moped #how to start a moped #how to start a scooter rental business #how to start an electric company #how to start electric scooterrental business #lime scooter business model #scooter franchise #scooter rental business #scooter rental business for sale #scooter rental business insurance #scooters franchise cost #white label app like bird #white label app like bounce #white label app like lime

Coding 101: Programming Language Building Blocks

This article will introduce the concepts and topics common to all programming languages, that beginners and experts must know!

Do you want to learn a programming language for the first time?

Do you want to improve as a Programmer?

Well, then you’re in the right place to start. Learn any programming language without difficulty by learning the concepts and topics common to all programming languages.

Let me start by answering the following questions:

• Why learn Programming?
• What is Programming?
• How to Learn a Programming Language?

Why learn Programming❔

Programming develops creative thinking

Programmers solve a problem by breaking it down into workable pieces to understand it better. When you start learning to program, you develop the habit of working your way out in a very structured format. You analyze the problem and start thinking logically and this gives rise to more creative solutions you’ve ever given.

Whether you want to uncover the secrets of the universe, or you just want to pursue a career in the 21st century, basic computer programming is an essential skill to learn.

_– _Stephen Hawking

Everybody in this country should learn how to program a computer… because it teaches you how to think.

_- _Steve Jobs

Programming Provides Life-Changing Experiences

Programming always provides you with a new challenge to take risks every time and that teaches you to take risks in your personal life too. The world is filled up with websites, apps, software and when you build these yourself you’ll feel more confident. When a programmer solves a problem that no one has ever solved before it becomes a life-changing experience for them.

What is Programming🤔?

A program is a set of instructions to perform a task on a computer.

Programming is the process of designing and building an executable computer program to accomplish a specific task.

Well, according to me programming is like raising a baby. We provide knowledge (data) to help understand a baby what’s happening around. We teach a baby to be disciplined (and much more) by making rules.

Similarly, a computer is like a baby. We set rules and provide data to the computer through executable programs with the help of a Programming Language.

(Photo by Clément H on Unsplash)

That’s it👍. If you can understand this basic concept of programming, you’re good to go. Pick up a programming language and start learning. Read the following section to get an idea of where to start.

My recommendation is to choose Python Programming Language as a start, because it’s beginner-friendly.

#programming #programming-tips #programming-language #programming-top-story #computer-science #data-structures-and-algorithms #tips-for-programmers #coding

Programming In Acceleration: Levelling Up Programming Skills

Some require and some are not. But acceleration programs might require you to build one. I’ll tell you how I made a computer program for the competition.

1-Researched the source codes and pasted it on my VS code

Written on the internet “blockchain-based ticket codes” and found the Ethereum source codes in Github. Then, I’ve just copied and pasted on my VS code by naming with .sol extension. Then, I’ve got my hands on the code itself and started to correct the mistakes that the editor has shown so far. Managed to reduce 189 errors to 58 within two hours. The rest was handled by my teammate when I sent the code I’ve edited. He just fixed the codes in three more hours and my mistake was not to increase the gas price. We increased the gas price on the remix and everything worked. And he just tested the software on scalability and security. It was the perfect garment for us that everything worked except the indentation errors.

What should’ve been done by us

Found all the codes including testing, copied them, and pasted them to our text editor for further analysis. Still, we had the prototype and we could write all the test codes, migrations, etc. if needed. Even more, we should’ve researched the codes to our project before using one of the examples.

#acceleration-program #program-analysis #programming #startup #acceleration #data analysis