Author: rolfje

JSON alerts for Munin

2018-01-07 rolfje 1 Comment

Munin is a great and easy way to monitor your servers. The documentation for Munin is kind of all over the place, and sometimes not all that clear.

There is the recent “Munin Guide” which is quite informative and well laid out.
Sometimes additional info and background can be found on the old munin wiki.

Getting the standard mail alerts working on munin is simplest, but as soon as you want custom layouts or send alerts as a push message to a phone, it can take quite some work. Here’s what I figured out to get the Munin alert available to you as JSON inside your own Python script so you can do anything you want with it.

Read More “JSON alerts for Munin” »

Software

Fixing a Jenkins 1.5 Slave on Windows 2016

2018-01-01 rolfje No Comments

When you configure a Jenkins 1.5x slave on a Windows 2016 machine according to the instructions on wiki.jenkins-ci.org you will probably get a warning that the .Net 2.0 is not available. This is reported as issue 21484 and the fix is to upgrade, which sometimes can be a problem.

If you can’t upgrade to the latest version for whatever reason, you can easily fix the .Net problem by changing the jenkins-slave.exe.config file from:

&lt;configuration&gt;
  &lt;runtime&gt;
    &lt;generatePublisherEvidence enabled=&quot;false&quot;/&gt;
  &lt;/runtime&gt;
&lt;/configuration&gt;

To:

&lt;!-- see http://support.microsoft.com/kb/936707 --&gt;
&lt;configuration&gt;
  &lt;runtime&gt;
    &lt;generatePublisherEvidence enabled=&quot;false&quot;/&gt;
  &lt;/runtime&gt;
  &lt;startup&gt;
  	 &lt;supportedRuntime version=&quot;v2.0.50727&quot; /&gt;
     &lt;supportedRuntime version=&quot;v4.0&quot; /&gt;
  &lt;/startup&gt;
&lt;/configuration&gt;

Hope this works for you. Cheers!

Software

Mattermost Delete Channel “fixed”

2017-10-26 rolfje 41 Comments

Users of Mattermost have probably noticed the less-than-optimal interface design where de Delete option is right above the Leave option in the Channel menu. On a busy server, you can imagine having quite a few incidents where people accidentally completely delete a channel.

In the Open Source version of Mattermost, everybody van do anything, because there is no sensible security model with roles. Mattermost Inc. seems to think that the Open Source community is not entitled to roles, which I (and others with me) strongly disagree with.

Forking Mattermost, learning Golang and enabeling security, improving a few other issues for the open source community along the way is a plan. But there is a simpler workaround for people running Mattermost inside Nginx.

Software

Installing GPG keys for Debian Backports

2017-06-09 rolfje 6 Comments

For Let’s Encrypt to automatically renew certificates on your Raspberry Pi, you probably want to install certbot. The installation instructions of certbot tell you to make use of the Debian Backports packages. Following the instructions to install backports packages into apt-get on raspbian (which is a Debian Jessie), you will probably run into the following error:

$ sudo apt-get update
...
W: GPG error: http://ftp.debian.org jessie-backports InRelease:
   The following signatures couldn't be verified because the public
   key is not available: NO_PUBKEY 8B48AD6246925553 NO_PUBKEY
   7638D0442B90D010

Software

Make the ESP8266 talk 9600 baud

2017-01-022025-10-17 rolfje 3 Comments

The default serial speed on the ESP8266 WiFi chip is 115200 baud. If you connect this chip to an Arduino and want to use SoftSerial to talk to it, it will not work. The SoftSerial library is limited to 9600 baud because of hardware limitations of the Arduino. If you want to talk to the ESP8266 with an Arduino at lower speeds, you need to tell the ESP8266 to slow down.

Hardware, Software

Seeed ESP8266 WiFi Breakout Board Pinout

2017-01-01 rolfje No Comments

WiFi Serial Transceiver Module Breakout Board w& ESP8266 pinout

This is the pinout for the Seeed WiFi ESP8266 breakout board. Please be careful, it only accepts 3.3 Volt nominal input voltage and logic. Putting 5 Volts on any of the pins may permanently damage the chip.

The ESP8266 on this board is programmed to do serial communications at 115.2 kilobaud, and accepts AT commands.

Hardware

macOS Sierra SSH “Permission Denied”

2016-11-12 rolfje 1 Comment

If you used DSA keys to log in to your SSH server and have upgraded your client machine to macOS Sierra (or OSX Sierra if you like), you probably ran into this problem:

client$ ssh -p 8123 george@10.0.0.10 -i ~/.ssh/id_dsa 
Permission denied (publickey).

The answer to this problem is replacing the DSA key with an RSA key, but how do you do on the server when your only means for connecting is the OSX client machine you just upgraded? Here’s how:

Apple

Designing a Fox-hunt antenna

2016-06-19 rolfje No Comments

Many years ago, I used to do some radio fox hunting with cars. Usually these hunts are at night to make it more exciting, and can be great fun. As I got older I lost interest and moved on to other things. But last year, I decided to have a go at a popular balloon fox hunt on 144MHz. This is quite a large scale and professionally organized fox hunt by Dutch Radio Amateurs.

Hardware, Workshop

Measuring Coax Length and Loss

2015-11-01 rolfje 4 Comments

Ever wondered how well your 50Ω coaxial cable is working? If you have a reasonably fast oscilloscope, preferably up to 100MHz and a signal generator which can generate short bursts, you can measure not only the length of your cable, but also the return loss at a certain frequency. From that, we can learn the attenuation of the cable.

This blog post describes the classic time domain reflection measurement using the following setup:

Measuring TDR

Hardware

How to get your users to install JCE

2015-09-04 rolfje 3 Comments

In every Java project where I need to do strong cryptography, I run into these dreaded unreadable stacktraces which send you into the woods. After a long search I usually discover that the Unlimited Strength Java Cryptography Extensions are not installed. To prevent frustration of users of your software, you can simply add a bit of informative logging to help him/her solve it when the solution is known.

Uncategorized