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Showing posts from March, 2014

Amazon EC2 experiences

Recently I was reading about Arscoins and the usage they made of the free Amazon EC micro instances. Intrigues I decided to take a look. Amazon have a free tier of services. Minimal devices with enough hours to run all month. I chose an Ubuntu Linux instance and after running through a simple sign up had an instance ready to go. Using shared keys I could ssh to it (the only way to go) and I had set firewall rules so that only a couple of static addresses could get to it. Amazing! It was all up and going in about 15 minutes. Only a barebones server of course but enough for testing and the obligatory oooh from my co-workers. The instance is free for 12 months and I've set alarms so that in the case of exceeding usage I will be notified of any billing. They also offer Windows servers too and a variety of different operating systems. For the minimal amount of time involved it was a great experience. I strongly recommend treating the instance like a server and keeping it updated and s

Hubsan X4 H107C 2.4GHz Quad Copter Adventures

Recently I acquired from eBay one of these: It's a little tiny quadcopter! I first became interested, not so much in RC, but in quads after watching the TEDTalk by  Raffaello D'Andrea  - The astounding athletic power of quadcopters . I found this amazing and further found it amazing watching this from TEDTalks by  Andreas Raptopoulos : No roads? There's a drone for that . These devices are pretty awesome and could revolutionise the way we do so many things - from deliveries to rescue, precision work in the air, even video recording at the Winter Olympics! Given the X4's small size I've been constantly surprised by it's speed and stability - even under fairly strong wind conditions. Throughout our house we have ducted air and when the A/C is up high the breeze is really quite strong. The X4 handles it quite well - I never use more that 60% of power to push against the air currents and can keep it fairly steady. Comparatively my much larger RC helicopters s

Using Nagios and SNMP to monitor network devices

Usage: check_snmp  -H <ip_address> -o <OID> [-w warn_range] [-c crit_range] [-C community] [-s string] [-r regex] [-R regexi] [-t timeout] [-e retries] [-l label] [-u units] [-p port-number] [-d delimiter] [-D output-delimiter] [-m miblist] [-P snmp version] [-L seclevel] [-U secname] [-a authproto] [-A authpasswd] [-x privproto] [-X privpasswd] Note: the -c and -w (critical and warning ranges respectively) reflect ranges differently depending on if you want a critical to be low (under 10 for example) or high (over 90). In the former case, say the Signal Level of a microwave device you are monitoring is critical when under 10% and warning under 20% then the format of the -w and -c would be:             -w 25: -c 10: If on the other hand you are looking at Signal to Noise ratio where warning is 50 dB and critical is 75 dB then the command would be:             -w :50 -c :75 If you have say a table where numbers translate to other things,

How to fix Nagios3 external commands error

After installing nagios3 and trying to send it a command to reschedule a check or do some other external activity you may get the following error: Error: Could not stat() command file '/var/lib/nagios3/rw/nagios.cmd'! The external command file may be missing, Nagios may not be running, and/or Nagios may not be checking external commands. An error occurred while attempting to commit your command for processing. In order to fix it, do the following actions: Check that /etc/nagios3/nagios.cfg has: check_external_commands=1 Also check that command_check_interval=15s is uncommented and command_check_interval=-1 is commented like this: command_check_interval=15s #command_check_interval=-1 Check the path for command_file is OK. It usually looks like this: command_file=/var/lib/nagios3/rw/nagios.cmd Make sure that the user www-data is part of the nagios group - this is located in /etc/group Check permissions on the command file that we looked at above: # ls -l