System Administration on bytebang

Streaming wireless weatherstationdata via MQTT

Tue, 29 Dec 2020 09:43:56 +0100

The Problem

A lot of 433 MHz based weather stations are sending their data to their paired receiver. But how would you receive all the stations within your vincity and stream the data into the internet ?

The Solution

rtl_433 is a tool which takes samples from an attached RTL-SDR stick and decodes them. The name already suggests that it will operate in the 433 MHz frequency area where a lot of weatherstations are boradcasting their values.

Stream your web/surveillance cam to YouTube

Thu, 26 Nov 2020 12:01:10 +0100

The Problem

If you have a cool webcam which should be streamed to youtube then you have a lot of options how to reach this goal. This article shows how to stream a webcam (or any other cam which offers a RTSP Stream) directly to youtube.

The Solution

First: Enable streaming in youtube. This will take up to 24 hours ! After this period you will be able to send a network stream to youtube which boradcasts it for you. Youtube offers a lot of help to get you started.

Manage your passwords with pass

Wed, 14 Oct 2020 18:01:03 +0200

The Problem

Everybody knows that passwords should have a certain amount of characters, numbers and special signs in it - which makes them hard to remember.

If you have a lot of different accounts then it is a good idea to store your passwords somewhere. People are coming up with different solutions to this problem

Sticky note under the keyboard -> not a really good idea
Excel Files -> Also not good, because these can be scanned by the windows search routine
Password managers -> GOOD IDEA

Within the Windows world, I would recomment KeePass as password manager. It is secure, fast and easy to use … but what tool should the plain linux user use ?

Reverse backup your Linux machine with a Synology NAS

Fri, 11 Sep 2020 21:05:52 +0200

The Problem

I think we don’t need to discuss that backups are a very convenient mechanism to restore accidentally deleted files or to recover your business from a malware / hacking attack.

A lot of companies (and also unaware sysadmins) are doing their backups with some kind of “Use some local rsync / robocopy script to copy all data to another drive / location” strategy.

Is this bad ? -> No! … you have a backup if you need one.
Is it good ? -> Well … it depends of how you do your backup in detail.

Imagine the following situation: You have a PC which is backed up by the previous mentioned strategy. All your backups are running regularly and then suddenly a ransomware comes along which tries to encrypt all your data. You might end up with an fully encrypted machine and also an encrypted backup - which renders it completely useless.

Stream public IPTV channels with TvHeadend

Wed, 05 Aug 2020 15:22:31 +0200

The Problem

I love to watch IP TV channels - and so do all my other flat mates. If only one person is streaming at a time then everything is fine, if multiple persons want to watch the same channel at the same time then the internet connection can suffer a bit.

Since I have a working Setup with TvHeadend on a Synology I wanted to integrate public available IPTV Channels into this solution. So every client can connect once to my TvHeadend Box, and the box connects one to the requested server(s).

Delete all emails in mutt

Sat, 02 May 2020 10:56:10 +0200

The Problem

I am running several Linux servers and thereon are a few cron jobs. I like to configure these cornjobs to send me an email with the result as soon as they are finished. (Which can be done by prepending a MAILTO=“recipient@adress.tld“ in the crontab)

However, if there are jobs which are running frequently then you may get a lot of emails in your local inbox. Since i am using mutt (a local command line email client) for checking my mails.

Forward RDP Connections through a Linux firewall

Tue, 07 Apr 2020 09:59:19 +0200

The Problem

When it comes to online learning some companies have it easier than others.While some can do this via plain PowerPoint Karaoke, others have to provide a complete infrastructure with different servers, services, specialized/expensive software packages and so on. Usually this is done via a separated learning environment (like a training-room within the companies facilities)

But if the trainees can not come to the training-labs (eg. because of COVID-19 isolation) then you have to bring this environment to them. voice and slides (or the screen of the presenter) can easily be achieved via

Getting Mikrotik winbox fonts right when emulated in wine

Tue, 24 Mar 2020 11:34:37 +0100

The Problem

Mikrotik sells very powerful hardware for really low prices. In order to configure the hardware you can either use NetFig (the web based configuration utility) or you can run winbox.

Winbox runs fine under MS-Windows environments, and for Linux geeks as me it can also be run within the wine environment (which is … as the name says … not an emulator).

Depending on what wine packages you have installed on your machine, you will encounter an imperfection if you are using the Terminal within winbox: The font is a proportional font - which is impractical if you want to render ASCII art tables.

Mounting a dd image

Thu, 30 Jan 2020 21:19:03 +0100

The Problem

Recently I had to re-setup my laptop because of *reasons*. However, I am used to backup it regularly by creating a full-disk image with dd which is stored on a separate hard disk.

dd is a tool which allows you to create bit-wise copies of disks or partitions into files and vice versa. The first few hundred bytes of a full-disk image contain information about the partitions contained on the disk.

How to connect your Davis Vantage 2 to the Internet

Sat, 30 Nov 2019 14:03:54 +0100

The Problem

I want to connect a Davis Vintage 2 weatherstation to the internet. The problem is, that the software that is usually available is pretty pricy - so i went for my own solution.

→ Photo of the Davis Vantage Pro 2 (external image, amazon.com)

The Solution

I was already using the Meteohub software package. I put a lot of effort to create all the graphs that i wanted and so I wanted to stick with it - so I had to find a way to make this software thing that it somehow has a RS232 connection to the station.

Turn Mikrotik CAP interfaces on and off by script

Mon, 29 Apr 2019 16:04:17 +0200

The Problem

I am running a big Mikrotik based WiFi installation where the Guest-Wifi should not always be accessible. One way how to do this is, is to create sub interfaces and to turn them on and of at the controller as you need them.

In the image above, we see some of the interfaces which are managed by CAPsMAN. The gues wifi is bound to the interfaces ending with the suffix _gast

Painless VPN with sshuttle

Thu, 28 Feb 2019 06:23:04 +0100

The Problem

If you are in a not very trustworthy network environment (e.g. free internet at the airport) then you may consider to send all your traffic (encrypted) through a VPN to a trusted site.
This usually requires some kind of VPN solution - but setting up a complete VPN can be a time consuming task. Here is a short solution how to redirect all your traffic with one simple command.

Connect to HAMNET with OpenWRT and a VPN

Sat, 26 Jan 2019 10:43:49 +0100

The Problem

I am a fan of ham radio operators digital backbone - the HamNet.

I wanted to be able to use it from my ’normal’ WiFi, with every device in my network. One way would be to set up a user access with a transceiver (e.g. a Ubuquity Bullet M2 HP) which is able to connect to the network and a decent antenna - but mine is currently used in another project. So i had to find another way how to do it.

TFTP boot with OpenWRT and a Synology NAS as storage

Sat, 29 Dec 2018 20:58:57 +0100

The Problem

From time to time I have to troubleshoot computers for friends or customers. Therefore I am using a lot of different live systems which can be booted via USB or from a DVD drive. I do not want to burn a DVD for every new release, and I also think that it is unhandy to create a bootable USB stick with every software I need.

Life would be so much easier if I could just save the image of a DVD onto my NAS and then be able to boot it via the network.

Porting LuaRTOS to the TTGO LoRa32 Board

Sun, 14 Oct 2018 18:34:27 +0200

The Problem

I have bought two cheap ESP32 based IoT development boards for around 30$, because the specs looked interesting:

ESP32 based with 3D- wifi antenna
128x64 pixel OLED display
LoRa Modem

This hardware has the potential to be a very versatile IoT prototyping (and even production) platform, but there was one drawback: You have to program it in the Arduino IDE. This means: You can do almost anything with it, but whenever you want to change something in the software then you have to recompile and upload everything.

Get rid of selfsigned certificate warnings in Ubuntu

Fri, 14 Sep 2018 12:34:27 +0200

The Problem

If I do some tele-work then have to access my files via a WebDAV server. This approach works pretty well - but there is one thing that annoys me: Whenever I am connecting to the server then this message appears:

The cause of this is that the (web-)server which sends the data towards me uses a self-signed certificate to secure the https connection. Since I do not control this server I had to find another solution than populating a letsencrypt certificate on it.

Find public IP address for OpenWRT via Script

Fri, 01 Jun 2018 23:23:33 +0200

The Problem

I was running a public server running behind my OpwnWRT firewall which was directly connected to the Internet via an LTE modem. The public IP Address of the OpenWRT Box was periodically announced via NOIP.com and so I was able to connect to it from wherever i wanted.

—–LTE—-> OpenWRT(Public IP: 123.45.12.34) —-> DMZ

Recently I switched my Internet provider and i got a new modem. This modem is now connected to the OpenWRT Box and acts as gateway to the Internet. It assigns a private IP Address to the WAN Port of the OpenWrt.

Find all manually installed packages within ubuntu

Tue, 20 Feb 2018 08:13:03 +0100

The Problem

If you plan to migrate your Ubuntu machine from one hardware to another then you can follow the following approach:

Perform a complete backup your home directory
Extract the list of manually installed packages
Set up a new vanilla Ubuntu on the same or another hardware
Restore the contents of your home directory
Re-install all missing packages

Now - where is the problem ? … If you don’t have a list of your previously installed packages, then it is not possible to use the new box as you have used the old ones - just because some of the programs that you are used to are missing.

How to migrate a vServer from netcup to another instance

Tue, 02 Jan 2018 14:24:14 +0100

The Problem

Well - I am a huge fan of visualization. This is the reason why several web presences (like simpledashboard.io and a few others) are running at virtual hosts at my favorite provider netcup.de

I like it to set up and customize my own web hosting solution - because then there are (except hardware limitations) nearly no other restrictions. But even with all this beauty, things tend to become complicated if your server reaches its limits - or just gets old. Then you have to upgrade to a new hosting plan with more powerful hardware.

Since I have not found any manuals how to do this I decided to write my own - here it is!

In the next few paragraphs, I will describe how I transferred my vServer from one hosting plan to another within 3 hours.

Recover your GPG profile from a GnuPG card

Wed, 13 Dec 2017 16:50:09 +0100

The Problem

Due to a crash I had to setup my computer from scratch. Usually this is with Linux not a big deal:

Do a plain setup of any linux favour you like
Install thunderbird and copy the old profille from backup into the new home
Install firefox and copy the old profille from backup into the new home
Install pass (a super cool passoword manager) and copy the password store from backup

… but wait - pass uses my GPG keys which are stored on my GnuPG card. How can i restore this to get pass working again to decrypt my credentials ?

Convert audio files with ffmpeg

Wed, 15 Nov 2017 09:55:13 +0100

The Problem

I have downloaded a youtube play list and wanted to listen to all the files on my mobile phone. Unfortunately my phone is not capable to play *.opus files. So i had to convert them.

The Solution

It is fairly easy to convert the files with ffmpeg.If you have only a few files then you can do this one by one at the commandline with the following statement:

$ ffmpeg -i myDownloadedFile.opus -f mp3 targetfilename.mp3

It converts the myDownloadedFile.opus into targetfilename.mp3.

Recover files from an encrypted home partition

Tue, 07 Nov 2017 17:08:03 +0100

The Problem

Assume that your computer does not want to start any more (e.g. because of a kernel panic during boot or a corrupted file system), and you want to make a last backup of your /home directory … well - this us usually not a big deal if your home directory is not encrypted.

BUT: If it is encrypted, then things tend to get complicated, because you can not easily access the files within the encrypted directory.

Enable https downloads with wget on OpenWRT

Sat, 14 Oct 2017 10:21:58 +0200

The Problem

I wanted to install a dns based adblocker on my OpenWRT 15.05.1 firewall. As I was trying to download the https://gist.github.com/teffalump/7227752#file-adblock-sh file my firewall denied to do so:

root@firewall:~# wget https://gist.github.com/teffalump/7227752#file-adblock-sh
Connecting to gist.github.com (192.30.253.118:443)
wget: can't execute 'openssl': No such file or directory
wget: error getting response: Connection reset by peer

The Solution

The problem there is, that wget wants to decrypt the https traffic, by utilizing the openssl command - which is simply not available. So the solution is to install the followng package: openssl-util

How to set up OpenWRT on a ALIX 2d13 board

Tue, 12 Sep 2017 23:07:14 +0200

The Problem

A friend gave me an old (but working) ALIX 2d13 board. Since my SOHO router was about to die (wifi keeps disconnecting and unstable throughput on the LTE band) I decided to give it a second life as router.

I wanted to have the following features as my old router:

LAN connection
Internetconnection via LTE
Wifi connection

The Solution

After a short internet research it was clear that the board itself is not the newest any more and it also does not have LTE or WIFI by default. So searched around a little and I found that I have an old broadcom wifi card with a bcm94318 chipset from an old laptop and an unbranded ZTE MF831 LTE Stick which can be used as LTE modem.

How to make static webpage snapshots with wget

Wed, 19 Apr 2017 22:23:54 +0200

The Problem

For some reasons I needed an offline copy of a certain homepage. Well, everybody knows that your browser can save a single page with a few mouse clicks - but what if you wanted to have a copy of the whole homepage ?

The Solution

I don’t know how the wayback machine (internet archive) does it but I came up with the following solution:

wget is a very powerful tool, which enables you to download arbitrary files from the internet. Beside that is has also the capability to download web pages recursively.

How to install node-red in Ubuntu

Mon, 20 Feb 2017 22:38:05 +0100

The Problem

I have an old laptop which runs Ubuntu 16.04, and I want to install node-red.

The Solution

This time the solution is really simple:

$ sudo apt-get install nodejs-legacy
$ sudo apt-get install npm
$ sudo npm install -g --unsafe-perm node-red

The first command instructs the operating system to install node-js (which is the base for node-red).

The second one installs a packagemanager for node-js (which does the same as apt-get, yast, yum, … for Linux, but for node-js)

Uninstall dpkg packages in Ubuntu

Sat, 21 Jan 2017 20:30:29 +0100

The Problem

I am running a Ubuntu box, and from time to tome I install trusted *.deb packages from the Internet. Since Ubunu is a Debian derivate this works without any problem.

Have you ever tried to uninstall these packages via the software center ? … Well: It turned out that this is sometimes not possible through the software center. This article shows you how to do this via commandline.

How to replace a failed disk of a degraded linux software raid

Fri, 30 Dec 2016 15:00:55 +0100

The Problem

One of my customers is running a 24/7 server with a mdadm based software raid that mirrors all operations between two disks (a so called RAID 1 configuration). Unfortunately one of the disks started to fail.

While the system was still running on the other (still working) disk I needed to replace the failing disk with a new one. Here is how you do it under Ubuntu and mdadm.

Renewal of a letsencrypt certificate for lighttpd

Tue, 20 Sep 2016 13:54:01 +0200

The problem

You have detected that your letsencrypt certificate expired, and now you want to renew it. This article shows how to do this on a machine called “support” which runs on Ubuntu 16.04 and lighttpd as webserver.

The Solution

The solution is simple. Just follow the steps below.

1.) Stop lighttpd

The first thing you have to do is to stop lighttpd (or any other service which binds to your webservers port 80).

How a keysigning party builds a web of trust

Tue, 17 May 2016 12:30:11 +0200

The Problem

Last month I attended a key-signing party at the Linuxtage in Graz. While I was pretty aware that key-signing is a great tool to prove your own identity against unknown third parties, I was not prepared what comes after the party. Here is a short write up, of what to expect from such an event and what has to be done after it. I try to keep it in a simple language, without too many technical details to give everybody the chance to understand what this is all about.

How to rename an application within IIS7

Tue, 09 Feb 2016 19:16:47 +0100

The problem

Our customer runs a reverse proxy server that connects to an in-house helpdesk system. This setup suddenly stopped working after an upgrade of th helpdesk system to a new version. It turned out that the problem is that the webapplication has changed its name and was therefore not reachable for the reverse proxy any more.

The upgrade of the web application changed the name /helpdesk to /Helpdesk (notice the upper case letter H).

OpenLDAP authentication for vTiger 6.0

Fri, 05 Feb 2016 22:44:41 +0100

The Problem

vTiger is a wonderful open source CRM system which has a very friendly license and offers a lot of features. It comes with a ton of preconfigured settings, but unfortunately a LDAP authentification is not in the box. If you crawl the internet then you will find answers on stackoverflow or this excellent article how to setup AD-auth for vTiger but these answers are tailored towards a Microsoft Active Directory structure. Since the Microsoft Active Directory is technically related to OpenLDAP we can use this approach to access our own LDAP directory. Lets go …

How to create a RAM disk

Sun, 03 Jan 2016 21:24:05 +0100

The Problem

Sometimes data has to be written and read ultimately fast. The random access memory is one of the fastest memories within a computer - it is not big, but fast. A cheap and handy solution is to create a tmpfs filesystem with a command like #mount -t tmpfs -o size=20% none /tmp/ramdisk - but this has a major drawback: As soon as the RAM get full data is beeing swapped out to the disk - which may be counterproductive.

Download multiple files with similar names within bash

Tue, 15 Dec 2015 21:20:54 +0100

The Problem

Assume you have a web server with interesting *.pdf files on it and all files are stored in the same directory. If you want to download them you would have to fire up firefox (or whatever browser you are using) and enter the URL for the document once.

http://my.server.tld/some/directory/Document_01.pdf
http://my.server.tld/some/directory/Document_02.pdf
http://my.server.tld/some/directory/Document_03.pdf
…

This is annoying and time consuming. Fortunately there is a tool called wget that can be used together with bash to automate this task:

Auto reconnect on dropped VPN connection

Sat, 21 Nov 2015 21:03:26 +0100

The Problem

One of my customers runs an external server which is connected to the main network via a simple PPTP connection. This works fine but from time to time the firewall decides to drop the connection (for whatever reason). From this moment on, the external server can not access the resources within the internal network any more. Until now we had to restart the connection by hand, but this is not very comfortable.

IPTV with a Synology DS713+

Mon, 19 Oct 2015 16:31:01 +0200

The Problem

Recently i purchased an Amazon FireTv Stick - which is a great device for video streaming. But I wanted more than this stick offers out-of-the-box: I wanted to be able to stream DVB-T and DVB-S (digital terrestrial and digital satellite) signals through my IP network. Somewhere in the internet I stumbled across a few articles which components are needed for this purpose, but in the end I had no idea if and how it would work. I wanted the setup to look like this:

Lexmark CX410 scan to network (on a SME Server)

Wed, 12 Aug 2015 21:09:43 +0200

The Problem

My local glider club bought a new scanner / printer combination from Lexmark. The CX410de is a good office device which is able to print and also to scan documents. While printing was no problem at all, the scann-to-network function bugged me (and my colleague) a lot. Scans to a normal windows box worked like a charm (exactly as described in the manual) but scans to a share on our SME server (which is basically a Linux box that emulates a Windows domain controller and some shares) failed constantly (“Verbindung konnte nicht hergestellt werden. Kontaktieren Sie Ihren Administrator” - which translates to “Network connection could not be established. Contact your administrator”).

Bypass restrictive firewalls with a SSH tunnel

Mon, 06 Jul 2015 19:46:48 +0200

The Problem

Free wireless LAN is offered in every bigger building or company. The problem with these wireless LANs is that the internet can be they can be (and often is) somehow restricted. Sites could be blocked, services can be disabled and traffic can be sniffed easily with a simple off-the-shelf firewall. Fortunately there is a simple solution to this problem: Encrypt your traffic, route it to a secure destination and surf the web from there on.

Autostart a program on the Raspberry Pi

Tue, 23 Jun 2015 11:42:32 +0200

The Problem

When you run a server then the server process has to be started. If you are installing a webserver like apache2 or lighttpd via the package manager then an autostart script will be installed as well. This is not the case if you want to run your self-compiled server like the dump1090 ADS-B receiver. In this case you have to provide the start (and also probably a stop-) script by yourself.

The Solution

The solution is simple. In the first step you have to provide a small script which starts and stops your server. In the second step you have to register it against the operating system. The exact procedure is described below.