RootUsers

How to check memory usage in Linux

In the Linux operating system it is important to have enough free physical memory (RAM) available for your processes which need to run. If this memory runs out, swap space will start to be used next, which will result in slower performance as I/O operations will need to be written to disk instead. If both main memory and swap become full your Linux system can completely freeze up.

By checking and monitoring the amount of memory in use and confirming there is enough free memory to service requests we can ensure that processes continue to run optimally.

How to enable the Telnet Client in Windows 10

Posted by Jarrod Farncomb on April 18, 2015 69 comments

By default the telnet client in Microsoft’s Windows operating systems is disabled, this is unfortunate as it is an extremely useful tool which can be used for testing TCP connectivity to external hosts on a specified port.

This is great when you’re trying to troubleshoot network connectivity problems, for example, say we have a web server which should be listening on port 80 to serve HTTP traffic but we are not able to load a web page, by using telnet to connect to the web server on port 80 we can verify the connectivity.

It may be that the connectivity is fine but there is a problem with the web server, or that the web server is stopped and the port is not listening at all, for instance. With telnet we can get a better understanding of what’s going on.

Free Virtualization Software for Windows

Posted by Jarrod Farncomb on April 15, 2015 3 comments

There is a lot of free virtualization software available for your to download and install, here we cover some of the best free options available for you to use in Windows.

These options can be installed within your existing Windows operating system installation, allowing you to run a virtual machine (VM) running an entirely separate operating system within. For example this will allow you to run multiple instances of Linux and Windows desktop clients or servers.

Best New Features in Windows 10 Preview

Posted by Jarrod Farncomb on April 8, 2015 No comments

When Microsoft first made the Windows 10 Technical Preview available I downloaded the free ISO straight away and booted it up into a virtual machine as soon as possible as I was excited to see what was new. My initial reaction at the time was “finally, something better than Windows 8” and I couldn’t wait to get the final version.

Windows 10 has since gone through many changes through the various new builds that have been released, so I have downloaded and started using the most recent build (10049) to review and share some of the best new features of Windows 10 that I have found so far.

Compiling NRPE and nagios-plugins for Solaris 11.2

Posted by Jarrod Farncomb on April 1, 2015 5 comments

I have some Solaris 11.2 storage servers which run a number of ZFS pools, I wanted to monitor these through NRPE via Nagios. To do this I needed to compile NRPE and nagios-plugins from source, this article covers how this was done.

Reverse DNS explained

Posted by Jarrod Farncomb on March 25, 2015 No comments

DNS is traditionally used to resolve a domain name to an IP address, this is known as forward resolution. Reverse DNS (rDNS) is the opposite of this whereby an IP address is resolved to a domain.

rDNS uses the arpa (address and routing parameter area) top level domain (TLD). The in-addr.arpa domain is used for IPv4 while ip6.arpa is used for IPv6 addresses.

This all sounds very backwards, let me explain…

How to use the hosts file to fake DNS

Posted by Jarrod Farncomb on March 18, 2015 3 comments

The hosts file is stored on a computer or device to provide local entries for DNS lookup. Normally when you try to resolve a hostname or domain, your computer will consult your specified DNS server to discover the IP address that it points to. This requires that there is an existing DNS server out there with the record that you require, with the hosts file you can fake DNS entries that will resolve only on the local machine.

Why would you want to do this? It’s great for testing or troubleshooting. You may want to use a specific hostname that no DNS exists for, though ideally you should create DNS records where possible as they can be centrally managed. It can help you get around DNS propagation issues, for example if a DNS record has been updated but had a TTL of 24 hours you may have to wait up to this long (assuming the cache cannot be cleared) before the record will resolve to the new IP address. By adding a temporary host file entry you can resolve to the new IP address straight away as the hosts file takes precedence over external DNS.

How to “ping” a port

Posted by Jarrod Farncomb on March 11, 2015 2 comments

Most of us would be familiar with the simple ICMP based ‘ping’ command which allows us to test for a basic response from some network connected device. While great for basic troubleshooting it does not allow us to confirm if the particular host at the other end is responding on TCP or UDP ports where the majority of services are likely to be provided.

Ping isn’t the be all and end all of network troubleshooting, if a firewall blocks inbound ICMP traffic then a ping will not succeed which can produce a false perception that the host is down as it is not responding to the ping, however other services could still be responding fine.

Alternatively while ping may come back fine with a response it doesn’t indicate if a web server is responding on port 80 for HTTP requests, the web server may have failed and no longer be responding.

So if ping is ICMP based, can we hit a TCP or UDP port for response instead? The answer is yes, let’s take a look.

How to fix template transfer in CloudStack

Posted by Jarrod Farncomb on March 4, 2015 No comments

While trying to transfer templates within Citrix CloudPlatform (Apache CloudStack) between different zones I received the below error:

sun.security.validator.ValidatorException: PKIX path building failed: sun.security.provider.certpath.SunCertPathBuilderException: unable to find valid certification path to requested target

This post covers how to fix this.

How to convert an OVA virtual machine to VHD

Posted by Jarrod Farncomb on February 25, 2015 19 comments

Today I received a virtual machine OVA file exported from VMware, I needed to import this into Apache CloudStack where XenServer was the hypervisor.

To do this I first needed to convert the OVA/OVF to VHD, this post covers how it’s done.

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