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…
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…
Network Policy Server (NPS) Notes
Audit policy CLI commands to set the success or failure to enable (Enable – enables logging). Get the current settings of the audit policy.
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…
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…
Useful Tools
Link Compilation Linux Useful Commands Linux Tool Alternatives
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…
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.
Enable older SSH key exchange methods
Insert the following in /etc/ssh/ssh_config. It will enable most algorithms that older devices may need. When connecting via SSH to older systems who do not support newer ciphers, you will sometimes get the following error: To permanently enable support for this cipher, you need to add the following line to either/etc/ssh/ssh_config to enable it for…
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.