Adding a new post about Hardening Linux Systems and SSH

content/posts/hardening-linux/hardening-linux.md

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+---
+title: Hardening Linux - An Update to Securing SSH
+description: "A Guide to Making Linux a Little more secure"
+tags: ["Linux", "Ubuntu"]
+author: "ahmza"
+date: 2025-06-05T15:34:10+01:00
+draft: true
+weight:
+featureimage:
+lastmod:
+---
+
+---
+{{< alert icon="fire" >}}
+> - This Guide assumes a Linux -> Linux SSH Session
+> - Please take care with production systems
+> - I take no responsibility for misconfigured systems and lockouts
+> - Try in a VM first and thank me later :)
+> - My Commands will be for Ubuntu Server 24.04
+{{< /alert >}}
+
+---
+
+## Introduction
+This guide will go over the basic steps of hardening a Linux machine with a
+focus on remote access. The reason this is important is because when we begin to
+expose services to the internet and make them publicly accessible then that means
+anyone can probe around.
+
+There are better ways around this especially if you are the only user, or If
+your users dont mind taking an extra step before being able to access your
+resources. If you have not heard of _Overlay Networks_ before they're similar to
+VPNs however do not need any open ports as they use NAT Punching AKA Hole
+Punching.
+
+Check out my post on [Tailscale](https://blog.ahmza.com/posts/no-more-port-forwarding/)
+
+regardless, it's always a good idea to implement good security practice so
+follow along and get your remote systems secure !!
+
+## Initial Steps
+
+Before we get into the meat and potatos of this guide, it would be a good idea
+to go over the following steps, especially if you are configuring a new install.
+
+### Software Updates
+Software updates are key for security as they will often include security
+patches. Depending on your flavour of Linux this command will vary.
+
+```bash
+sudo apt update && sudo apt upgrade
+```
+{{< alert "bell" >}}
+If you do not expect to be logging into this remote machine very often it may be
+a good idea to [setup automatic updates](https://blog.ahmza.com/posts/setting-up-automatic-updates)
+however if you want more control then using [Ansible to update Remote Machines](https://blog.ahmza.com/posts/ansible-to-manage-remote-servers)
+would be a better option.
+{{< /alert >}}
+
+### User Accounts
+It's not a good idea to continue to use a root account after install, it's much
+more secure to setup another user account with sudo access. The reason is the
+root account has complete control over the system, where a user account is more
+restricted by default. As well as this logging is more granular with different
+user accounts.
+
+The following command will allow you to create a new user, it will also ask you
+some questions about user information however the only required fields are the
+username and password if you want one.
+
+```bash
+adduser username
+```
+
+now we can add our newly created user to the sudo group to give admin permissions
+
+``` bash
+usermod -aG sudo username
+```
+
+{{< alert "bell" >}}
+Remember to replace username with your desired username
+{{< /alert >}}
+
+you can now logout of root and log back in as your user. Further action on the
+server should now be executed from this user account.
+
+## Creating SSH Keys
+Now that you have your own user account, we can create an SSH key for it. An SSH
+Key is a Public and Private key pair which allow client and server to
+authenticate using Public Key cryptography. Public Key cryptography is much
+harder to crack compared to a password, as well as this we no longer need to
+send passwords across networks which can be at risk of interception.
+
+SSH can also be more convenient once you set up ssh-agent which will be covered
+later in the guide, with password authentication you need to enter a password
+everytime, however with ssh-agent you can enter your ssh-key password once and
+it remains unlocked for the remainder of the session.
+
+{{< alert "fire" >}}
+**IMPORTANT:** **NEVER** share your private ssh key ... it's private for a reason.
+{{< /alert >}}
+
+By running the following command you will create an ssh-key !!
+```bash
+ssh-keygen -t ed25519 -C NameYourKey
+```
+- `-t` - specifies the type of cryptographic algorithm we will use
+- `-C` - notice it's capital, A name for your ssh keys. I usually give them the
+hostname of the local machine
+
+## Conclusion
+