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Category: Linux

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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October 16, 2023October 16, 2023

Expand Logical volume in Linux LVM

LVM makes it easy to resize volumes in Linux. This can be done without unmounting drives orrequiring a restart. First determine the free space of the group volume. First determine the partition where your OS is installed. Expand the partition. Here we will assume that the partition is sda3. You can view the volume grow…

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June 25, 2023July 16, 2023

Useful Tools

Link Compilation Linux Useful Commands Linux Tool Alternatives

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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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March 23, 2023July 1, 2024

Enable older SSH key exchange methods

Insert the following in /etc/ssh/ssh_config to apply it system wide or ~/.ssh/config for just your user. It will enable most algorithms that older devices may need. You might get the following error when accessing old SSH servers on Fedora or other RedHat based distributions with weaker keys. To allow these weaker keys, update the crypto…

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March 15, 2023March 15, 2023

Yarn Repository Expire Key Error

When using yarn through the apt repo, the key might expire, giving you the following error when updating apt. Issue the following command to update the key and then update the repository.

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November 9, 2022November 9, 2022

Create a .pfx/.p12 Certificate File Using OpenSSL

Source: https://www.ssl.com/how-to/create-a-pfx-p12-certificate-file-using-openssl/ The PKCS#12 or PFX format is a binary format for storing the server certificate, any intermediatecertificates, and the private key into a single encryptable file. PFX files are usually found with theextensions .pfx and .p12. PFX files are typically used on Windows and macOS machines to import andexport certificates and private keys. Requirements…

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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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