Code Snippets

RightScale RightScript To Update CentOS iptables Rules On RackSpace Node

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.

Technology Insights

Move Long Running Linux Process To Screen Session

Have a long running Linux process open in a SSH terminal window and need to shutdown your computer without killing it? I run into this on a regular basis and never spent the time looking into a solution but this past weekend I actually decided to look and came up with a cool solution called reptyr. The reptyr application allows you to open screen and migrate the process to the screen terminal and away from the terminal connection opened without screen. This allows you to detach from the window without killing the process. Below is a quick overview of installing reptyr and how to use it.

Technology Insights

Exclude Multiple Directories When Creating A tar Archive

Earlier when upgrading a WordPress site that is running on a CentOS Linux server I needed to quickly backup the entire site to then perform an upgrade of the core WordPress installation. There are multiple directories located beneath the primary site folder that I didn’t need to backup including some caching directories as well as a database backup directory since all of those directories are not required to restore the site in case of an issue during the WP upgrade. Use the information below to create a tar archive while excluding multiple sub directories.

Technology Insights

Find Out The Amount Of Time A Linux Process Has Been Running

I always forget the ps command arguments to see the length of time that a Linux process has been running so I am writing it out here in hopes of remembering it in the future without having to read the ps manpage. I also will know I can easily search this later to find the solution. Below I describe what command to use from a Linux terminal window to display the length of time a specific process or set of processes has been running.

Technology Errors

CentOS Linux Parted Error: Unable to open /dev/sdc – unrecognised disk label

While rebuilding a large RAID 5 logical drive I had to use parted instead of fdisk. It has been awhile since I had to build a logical drive that was over 2TB so it had been quite awhile since I have used parted which will perform the same basic functions as fdisk and more. Anyhow when first attempting to use parted to create a partition table on the logical volume sitting on top of an Adaptec RAID card with multiple 2TB drives configured as RAID 5 on CentOS Linux I ran into an error. The resolution is easy but needed to note for myself as much as anything else.