How to impersonate another Linux user using SUDO
sudo -i -u mary You need to use the -i (login) option. Reference https://www.howtogeek.com/447906/how-to-control-sudo-access-on-linux
Security
How to deal with ACMEv1 is deprecated and you can no longer get certificates from this endpoint. Please use the ACMEv2 endpoint
Whilst trying to renew a Let’s Encrypt certificate on an older CentOS server, you might experience the following: Cert is due for renewal, auto-renewing… Starting
How to never get phished
There are technical ways to look at any website and email to determine what the actual links are. Phishers are sophisticated criminals and try to
How to install chkrootkit on CentOS 7
chkrootkit is a tool that’s used to determine if a Unix server has been compromised. You can’t do yum install chkrootkit on CentOS so follow
Fail2ban Postfix SASL Troubleshooting
Background On some Virtualmin server you may find that Fail2ban is logging events, but soon realize that due to the amount of “already banned” messages
iptables cheat sheet
What is iptables? iptables is a powerful firewall utility for Linux that is often included with the operating system. Behind the scenes many firewalls also
How to check and remove IPs from fail2ban
Background Fail2ban is a really powerful utility and can help you out of a bind. The problem is the syntax – it’s changed and when
How to use sudo and su to elevate yourself to root and then to another user
At times on a Linux server you want to switch to another user. One example could be one a shared server whereby you need to
How to generate RSA public and private key pair in PKCS #8 format
This article explains how to create RSA public and private key pairs in PKCS#8 format. This might be required if an upstream supplier asks
Fail2Ban ssh-ddos Issue with New Install of Virtualmin and Ubuntu 18.04
Background On a newly installed Virtualmin server you might see events complaining about a missing config file for filter.d/sshd-ddos as per below: Jul 13 19:57:35