• Stay away from suspicious access with fail2ban

    A number of suspicious access to Linux servers happens on the Internet every day. Fail2ban is software to protect Linux servers from brute-force attacks. Installation on Ubuntu Linux server: $ sudo apt update $ sudo apt install fail2ban Configuration of Fail2ban: Configuration files are located in directory /etc/fail2ban. An example checks the status & unban […]

  • 550 5.7.511 Access denied, banned sender

    Before the Christmas holiday, some of our clients using Linode cloud servers reported that emails cannot be delivered to some domains hosted at Microsoft Office 365 from their Postfix SMTP server. We checked that all of them are still in good reputation and not listed in other email block lists, but only Microsoft Office 365 […]

  • How to setup a email relay with the Postfix SMTP server ?

    Email relay is an email server which forwards incoming SMTP emails to an another SMTP server. Postfix can be setuped as an email relay. First, you should ensure which domaisn are being forwarded (eg. domain-A-to-be-relayed.com and domain-B-to-be-relayed.net), and hostname of destination SMTP server which you expects emails for these domains forwarding to. (eg. destination_host of […]

  • How to manage KVM Virtual Machine

    How to manage KVM Virtual Machine

    virsh is the administration tool of KVM virtual machine, for examples, starting up or shutting down VM operation, control and modify the virtual machine, etc. virsh can be used as an interactive command shell or direct execution with its sub-commands. List KVM Virtual Machine and their names ‘virsh list’ lists the running KVM virtual machine. […]

  • How to build KVM virtual machine on Ubuntu 16.04

    How to build KVM virtual machine on Ubuntu 16.04

    KVM (Kernel-based Virtual Machine) is the virtualization solution supported on Ubuntu and other Linux distributions, it is added to mainstream Linux Kernel from version 2.6.20. QEmu is the complete KVM emulator.  Many cloud servers are running as virtual machines, its advantage is rapid deployment. A number of machines can be added in a short time […]