Perl: Sort Hash Values by Key with a Hash Slice

In Perl, hash (associative array) sorting is a common and easy practice. Sorting values by key is easy. And so is sorting by value. But how do you sort the values of a hash by key? One answer is to use a hash slice. Continue reading

Simple Nextcloud Installation on Raspberry Pi

This article was revised and updated on 27th May 2017.

The Raspberry Pi’s low power consumption makes it well suited to the role of always-on web server. This post describes how to install Nextcloud onto the Pi.  Nextcloud is an open source software package providing remote file sharing services, similar to Dropbox. But with Nextcloud, you retain ownership, security and control of the shared data. Nextcloud works well on a Pi 2 and Pi 3 but will run very slowly on a Pi 1.

The below procedure describes how to install Nextcloud version 12.0.0, the latest stable version at the time of writing (27th May 2017), but it should work for later/future versions too.
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ESXi Embedded Host Client

The ESXi embedded host client is a web application served direct from an ESXi server that allows basic management of virtual infrastructure. It is somewhat similar in appearance to Vsphere, though the feature set at the moment is less rich. Vmware has released it as a “fling“, which can be easily added to an existing ESXi server as follows. NB it is recommended to try this in a lab environment rather than a production machine. Continue reading

Linux Capabilities and Ping

If you are running a recent version of Linux (time of writing May 2016), you might encountered this error with ping:

$ ping somehost
ping: icmp open socket: Operation not permitted

It happens because the ping binary is no longer installed with setuid root rights. It doesn’t have the required priveliges to open the socket, and fails. The quick fix is to type: Continue reading

Protect Your Web Server With Ipset

The Linux packet filter provides an easy way to protect against unwanted network intrusions. Often referred to simply as “iptables“, it is a basic firewall built into the Linux kernel. Iptables is most useful, perhaps, on those servers most susceptible to attack, such as LAMP systems, content management servers and blogging platforms, especially where they are Internet facing.

Ipset is a fairly recent addition to Linux, having been introduced into kernel version 2.6.32. This means it is supported in Debian 7 and 8, as well as Red Hat 6 onwards. In short, ipset allows a large number of IP addresses to be blocked in an efficient way, as demonstrated below. Continue reading

Linux Device Change Breaks Encrypted Swap

Linux disk partition names such as /dev/sda1, /dev/sda2 are not as fixed as they once were. From time to time they can change. Perhaps due to a hardware change or kernel upgrade, or sometimes for no apparent reason. If and when this happens on your system, things can break. In this case, an encrypted swap partition had been configured as “/dev/sda6”, and failed to activate following a change in the the /dev/sdXX partition names. This article describes the symptoms and a fix.

The article also discusses a bug affecting Ubuntu 14.04 based distributions, which can make it more difficult to recover an encrypted swap configuration broken by a device name change. Continue reading

Debian 7 to Debian 8 Migration Gotchas

Debian 8 (jessie) was released in April 2015, ten months ago at the time of writing. Some sites will have upgraded by now, and others might be considering the move. This article provides a list of issues encountered after upgrading several servers from Debian 7 (wheezy) to Debian 8. These are system administration issues in the most part, though some might also be of interest to application support staff. Continue reading

How to Rename the Default Raspberry Pi User

The Raspberry Pi comes with a default user called “pi”, whose initial password is also set to a well known default. While this makes it easy to use the system, it is not very secure. Anyone with physical access to your Pi could login with these widely known credentials. Furthermore, if you have enabled the SSH server, users on the local network could do the same.

Even if you have changed the “pi” user password, just having a user name that is universally known is still a security risk. The following article explains how to safely rename the “pi” user to something more secure. Continue reading

List Virtual Machines on ESXi

ESXi is popular hypervisor product from VMware. It comes with several management GUIs including Vsphere and VCenter. Command line tools are also bundled, though they are used more rarely. This article describes a short script to list all virtual machines on the system.

The script is below. It is intended to run under the Busybox shell, the default environment when you ssh directly into the system hosting ESXi. Continue reading

Some Raspberry Pi 2 Benchmarks

This article presents a few informal benchmarks comparing the Raspberry Pi to the Raspberry Pi 2. The original Pi has a single core ARM v6 processor. The Pi 2 is quad core, ARM v7, and clocked faster than the Pi 1. But is it really six times as fast, as the makers claim ? Short answer: yes it is. And then some. Continue reading