Earlier when installing snort on a CentOS Linux server I ran into a configure error. The error related to the fact that libdnet was not located on the server and while it was installed I did not have the libdnet-devel package installed. Below is the sample output from the configure error, an expandable complete output of the configure error, and the yum command to install libdnet-devel to move past this error when installing snort.
Earlier while analyzing a Linux server it was pointed out to me that the Apache logs were filling up with constant connections requesting domains that were not configured on the server. To me it looked as if a load balancer somewhere was misconfigured and sending traffic to our IP address by mistake but I needed to open a ticket with the colocation provider to have them look into the issue further since the network in this case is not something I have any control over. Below is a quick Linux command that will output a list of IP addresses making port 80 connections to your server.
The below code snippet was used to add SSH users to RackSpace cloud CentOS Linux nodes being used as application servers and managed via RightScale. The SSH users were required during a testing phase so they could look through logs and make modifications to specific configuration files, etc. There are three things that have to happen to create the SSH user, allow them to login, and provide them the necessary rights on the server to accomplish their tasks which include adding the user, modifying the sshd config to allow password logins, and update the sudoers file to enable sudo access for wheel group users.
Recently I was working on a project that was using RightScale to manage RackSpace cloud nodes. One of the requirements of the project was to have application nodes scale automatically thus they were required to automatically install software, configure settings, and start services automatically on the RackSpace CentOS nodes being used. Most everything was fairly straight forward however some of the services we were using would not start properly and initially because of the lack of logging from the services we were unable to figure out what the problem was. Below I describe the problem in more detail along with the solution which involved updating a configuration file on the CentOS Linux servers and then restarting the services.
Recently while working on some node or instance automation using RightScale I needed to have some extra iptables rules created automatically when a new node booted. Initially I was just trying to do this via iptables commands which I note below but it would never work. After digging through the logs I realized that the iptables commands created by RightScale for the ServerTemplate I was using flushed iptables at the very end of the boot process and thus wiped out the iptables entries created by the RightScript I had created. To accomplish permanent iptables entries for a RackSpace node via RightScale you need to output the iptables command to a file in the location where the boot process picks them up after flushing the current ruleset. Below I describe my first attempt followed by the correct way to have iptables entries picked up by RightScale.