Category Archives: Linux

Virtualization hypervisor and containers all in one

I’m a big fan of virtualization, the ability to run multiple platforms and operating systems (called guests) in a single server (called host) is probably one of the best computing technologies of the past 10 years.

Personally, I have been using virtualization circa 2004. It all took off after 2006 when chip manufacturer’s started bundling virtualization technologies in their processors (Intel VT-x or AMD-v). The reason why “cloud” computing is so popular can also be attributed to virtualization.

In a container world…

However, in the past couple of years a new technology has been making making the rounds everywhere, the words “containers”, “docker”, “orchestration” is picking up steam in the past year. They say that containers are changing the landscape for system administrators and application developers.

Claims that containers can be built and deployed in seconds, share a common storage layer and allow you to resize the container in real-time when you need more performance or capacity are really exciting concepts and I think the time is now for me to jump in and learn a thing of two about this new technology when its hot a new. Continue reading

Plex mediaserver on FreeNAS allowing anyone to stream without login

I’ve been a user of Plex mediaserver for over two years, I set this up on a FreeNAS jail a long time ago and in the past few days I noticed something funny.

Out of nowhere there were two additional streams going on in my server onto the internet, I usually share my library with friends and family but what was curious about this traffic was that Plex was claiming that these two streams were “on my local network”
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cPanel DNSonly bind recursion

In case you may be running into issues with named/bind domain service on cPanel DNSonly not responding to DNS queries recursively, I have a fix for you.

In older versions of named/bind9 used by cPanel if you wanted to allow anyone (or if you wanted security you could have setup an ACL, let’s assume you want to allow all) you could simply edit the configuration file and change “recursion no;” to “recursion yes;” to allow anyone to make queries to your DNS server for those domains or records that are not kept in your local server (ie: resolve
Newer versions of BIND9/named changed their past behavior and now require a more specific configuration, just add these under “options” section

options {
allow-recursion { any; };
allow-query { any; };
allow-query-cache { any; };

I found a detailed explanation on why bind/named dns server changed its behavior, on the next page  a copy of the support bulletin from July 2007:

Overriding Google Compute Engine hostname from getting reset

On my last post, I explained how I am experimenting with Google Compute Engine (GCE) to host my backup DNS service and my post about configuring mailjet as an exim mail relay.

I have run into a few issues on Google Compute Engine, it looks like every time the instance gets a DHCP offer the hostname of the machine will get reset to the internal hostname, overriding whatever setting you may have set… this is bad news for a server that needs to respond to DNS settings.

After a few hours of digging and testing out different approaches, including trying to setup a DHCP hook to run the “hostname” linux command I came across documentation from Google talking about “custom metadata”.

How to setup Mailjet on exim for cPanel dnsonly on Google Cloud

I have been experimenting with Google Compute Engine (GCE) for the past few days. I wanted to migrate a slave DNS server to Google as an experiment and this blog post will talk about the shortcomings, my workarounds, configuration and tips to achieve the goal of having cPanel DNSonly installed and setup using Google’s infrastructure.

What is Google Compute Engine?

Google Compute Engine (or “GCE”) is Google’s answer to Amazon’s AWS, it basically offers you the ability to deploy Virtual Machines (VMs) at Google’s datacenters. In the most simplistics of setups you would use a single VM or “compute instance” and if you wanted to have a more complex setup you could deploy multiple instances in different geographic locations spread across different datacenters in the United States to achieve a more redundant setup or to provide you with better capacity for large traffic workflows.

It all depends on what your goals are, myself I am just starting out with a simple requirement. I would like to use a single compute instance running CentOS linux that runs cPanel DNSonly (proprietary control panel/dns clustering solution for cPanel servers).

The goal is not to host websites or any critical services on this instance, but rather only keep a copy of my DNS zones. If my experiment fails or my instance goes down or gets destroyed there won’t be any losses or damages for this experiment as my primary server is still running on Proxmox PVE.

The limitations of GCE… What I learned so far

GCE instances run behind Google’s firewalls and depending on the datacenter you decide to host your instance your VM will have an internal IP within that datacenters network scope/range (for example: us-central1 datacenter zone has a range for all VMs).

This means that assigning a IPv4 public static IP, which is needed to allow anyone to query the DNS server we’ll be hosting inside this instance will actually have to forward packets to the instances internal network. Not really a big deal unless your application can’t be behind a NAT firewall like it is the case here.

For our intensive use and purposes it is fine. One important issue that I found is that doing any kind of e-mail server related activities on GCE is prohibited (source). You won’t be able to use SMTP (Simple Mail Transfer Protocol) port 25, 465 or 587 to send or receive email.

Now for a DNS server that will not be a mailserver this is not a blocker, but it is really a pain in the ass. Why? because monitoring scripts running on the server need to email the administrator to notify me of issues or errors so they can be investigated.

Continued on the next page.

Building a low power Sandy Bridge ESXi + ZFS Storage Array

I have finals this week, so I will update this post as I have more time. In the meantime, I am working to get vmware ESXi (free version of vmware Virtualization server hypervisor) onto a custom whitebox build to replace my aging Intel Core 2 Quad Q9450 server that uses around 125 Watts while idle. Continue reading

Find disk by id in Linux

You may be wondering why linux is not pointing to a standard /dev/sdX for your SATA hard drives. When you come across a reference to a hard-drive in the ID form like this:


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SecureCRT mapping “Page Up” and “Page Down” for Nano/SSH

If you use a windows ssh terminal client, or even macosx’s, the functionality of your page up and page down key may not behave like you want it to. For example, in SecureCRT using pageup will actually page up your scroll buffer, and pagedown will scroll down your page buffer.

You’ll need to remap your keys to send the correct signal to your terminal. Change it from the default system function to “send string” and the following strings:

PageUp = 33[5~
PageDown = 33[6~

33 is a shortcut for the ESCAPE key (esc) since in some programs you can’t type in the actualy escape key.

Here are some other codes as well in case you need to remap keys.

Pause = 32
Macro = 03 # Break (Shift-Pause)
Home = 33[1~
Insert = 33[2~
Remove = 33[3~ # Delete
End = 33[4~

In SecureCRT the area to remap your keys is Tools -> Keymap Editor.

This is especially handy if you use command line IRC clients such as Irssi or BitchX.

Add additional IP’s on different subnets using same Ethernet card on PVE

To do this, we need to add a custom route to the server, we need to add the network and netmask addresses, to test and see if it works:

route add -net netmask dev vmbr0

if it works, add the following to your /etc/network/interfaces file

iface vmbr0 inet static

bridge_fd 0
up route add -net netmask dev vmbr0
down route del -net netmask dev vmbr0

did not work? Remove route with:

route del -net netmask dev vmbr0

Finding segfault core dumps

Find core dumps

find . -type f -regex “.*/core.[0-9][0-9][0-9][0-9]$”

The regex in the above command matches the file name “core.xxxx” where “xxxx” is exactly four numbers 0-9. If the results look correct, we can delete all those dump files with the following command.

Find + Delete all core dumps found

find . -type f -regex “.*/core.[0-9][0-9][0-9][0-9]$” -exec rm {} ;

The one downfall of this method is that it’s slower, since regular expressions take time to process. But this is a small price to pay for getting rid of these files in large numbers safely. If you see any errors with the above code or have any experiences to share please leave a comment below.