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Tag: ubuntu

June 24, 2024June 24, 2024

Service check / Port check in LibreNMS

LibreNMS offers a way to check for services and/or ports. In this example, we will check for HTTPS/SSL. First we need to enable services. Make sure the value for show_services is “1”. If not, change it to “1”. We then need to install the nagios-plugins. Let’s add a dummy device. In this case, we will…

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May 18, 2024May 18, 2024

CrowdStrike: Update to supported kernel to remove RFM status in Ubuntu

To get the full benefits of the falcon-sensor on Ubuntu, you need to use a supported kernel, or your system will be in “RFM”. To remove the RFM status we will need to update to a kernel supported by your version of falcon-sensor. First verify your RFM status. You should see the following in the…

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November 20, 2023November 20, 2023

Create a shared SFTP chroot directory for multiple users

These are instructions to create a shared directory amongst two or more users. This will only allow those users access to SFTP, but not the shell. They will also be “jailed” to the directory of your choosing. These examples were done using Ubuntu 22.04 and assume that you are root or using sudo. You are…

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November 17, 2023May 30, 2024

Add Duo Two-Factor auth to SSH in Ubuntu

Duo offers a relatively simple way to add support Duo two-factor auth to SSH sessions in multiple Linux Distributions. Here are my steps for Ubuntu Server. Create /etc/apt/sources.list.d/duosecurity.list with the following contents: Create a user that corresponds to your username in Duo. Add your user to sudo group (Ubuntu) or wheel group (RedHat) Install the…

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October 16, 2023November 15, 2023

LibreNMS – Notes On Upgrading from Ubuntu 20.04 to 22.04

These are the steps that need to be done when doing an in-place Ubuntu upgrade on a LibreNMS system using do-release-upgrade. Running daily.sh in /opt/librenms should give you most of the errors you need to fix that we will go through in this guide. Most commands here will assume you are running as root or…

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June 22, 2023July 9, 2023

Allow SSH connections only from certain addresses using hosts.deny/hosts.allow

This is the method that can be used to allow SSH connections from certain IP networks. An example use for this is allowing SSH from certain public IP networks, as well as from my Tailscale network. If possible, it is probably better to use iptables/nftables/ufw or the firewall feature of your hosting provider if they…

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June 9, 2023July 20, 2023

Rate limit connections in Linux

Use the following iptables command to rate limit connections per IP. This is useful for preventing a DDoS attack on DNS servers. However, for DDoS protection for your DNS servers, you should be hosting DNS with the big cloud providers like Cloudflare, or running dnsdist in front of your authoritive servers.

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Disclaimer

These posts are notes for me. These are not guides and you should not use these instructions as step-by-step instructions without knowing what they do.

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