Dariusz on Software Quality & Performance


Simple mailing list on Debian in 3 simple steps

Filed under: en — Tags: , — dariusz.cieslak @

E-mailFew days ago I launched simple low-traffic mailing list using naive /etc/aliases method, but got the following error:

<example1@onet.pl> (expanded from <example@myserver.com>): host
mx.poczta.onet.pl[] said: 554 5.7.1 <example1@onet.pl>:=
Recipient address rejected: Spf check: fail (in reply to RCPT TO command)

If you think for a moment the reason for error it's obvious. My server tried to forward e-mail using original From address.Onet.pl checked TXT record (using SPF standard) for my server domain myserver.com and noticed it's not allowed to send e-mails from me.

In order to make things work properly one have to rewrite envelope From field properly. Mailing list managers usually do that properly (/etc/aliases is not enough).



Automated RTP headers analysis

Filed under: en — Tags: , — dariusz.cieslak @

rtp1IPTV technology delivers video streams using fast, but not reliable protocols (UDP). Those connection-less protocols do not guarantee delivery nor retransmissions of missing packets. We have to accept low video quality for some networks or add another layer above basic protocol that allows to control completeness of delivery. For this purpose we use RTP (packet order, completeness) and RTCP (retransmission requests) protocols.

In this port I'm going to show how effectively use Linux command line tools to analyse client – server cooperation regarding retransmissions for complicated real-world example. Basic RTP metadata collected by tcpdump is used as an input.



Wavemon – monitor your WIFI connection quality

Filed under: en — Tags: — dariusz.cieslak @

The old truth that everyone who spends days on business trips: hotels generally sucks at local Internet delivery service. The least important service in hotel is pretty crucial if you depend on it to finish some work after business hours.

However, if you are on Linux/Ubuntu machine there's a nice tool that will allow you to evaluate WIFI signal quality. It's name is: wavemon. It's a console tool that shows current (and previous) signal strength.


Having real-time measurement you can decide what area of the hotel have the best signal strength.


"Keep It Simple, Stupid" by UK goverment

Filed under: en — Tags: — dariusz.cieslak @

I was searching for current UK VAT rates as my client operates on this marked and found the following official page that was a delight for my eyes:


Compare that with all that bloat you expect from your government and you know why some countries are much better for business than others.


Computers's helping hand

Filed under: en — Tags: — dariusz.cieslak @


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