STICKY: Useful Unix commands

For a long time I’ve maintained a memory aid in the form of a list of useful commands which can be used on the command line for Linux, OS X, BSD, Solaris, etc., so I thought I’d list them in a blog post in case they come in useful for others. Most of these will run on any Unix-type operating system, though I’ve usually indicated where a command is OS-specific. read more

COVID-19 update

CETRE SysAdmin Services continue to operate as normal during the Coronavirus pandemic and lockdown. Matt’s services are available for organisations feeling the strain during this difficult period, who are looking to keep their infrastructure up and running as efficiently as possible with minimal costs and resource usage. Matt’s services are also available for organisations taking advantage of this slower period to make improvements or launch projects requiring new infrastructure and devops engineering.

Script to detect MAC addresses of new devices connecting to local network

I wanted to get notified of any new machines connecting to my local network so that I could be reasonably sure there would be no unauthorised devices connecting wirelessly to use my network for unknown and potentially malicious purposes. I therefore wrote a simple script to detect new MAC addresses appearing on the network and notify me accordingly. The script requires nmap to be installed and should ideally be run from cron with the output going to a valid email account. The script can be obtained from my GitHub.

No Man’s Sky – musings and wallpapers

It’s unusual for me to take much interest in anything with so much hype, but I thought I must make an exception for No Man’s Sky, a game which brings together two things I’ve treasured during my life: firstly, the concept of space exploration in a computer game, as originally explored in the form of the glorious game Elite which I spent a great deal of time playing as a teenager; and secondly, graphics inspired by wonderful 70s sci-fi artwork such as that produced by Chris Foss, which I’ve enjoyed in books since my early childhood. I was so keen to play this game that I even went so far as to buy a new PS4 so I could play it. read more

Reclaiming storage space on two-node MongoDB replica sets

At mongodb.org they seem to assume we can create MongoDB replica sets using unlimited numbers of instances which have infinite amounts of storage. In practice, however, we often need to use replica sets with only two nodes (plus arbiter) which have limited storage. The problem then is that MongoDB has the tendency to use vast amounts of disk space without reclaiming the space from dropped data, so it consumes ever-increasing amounts of storage. It’s then hard to deal with this storage problem given the limited options available in a two-node replica set. read more