Test TCP connection without telnet or nc

Sometimes you need to test if a network connection works without actually using the intended client program. Normally you would use a tool like telnet or nc to do this, e.g. $ telnet www.google.com 80 Trying 172.217.20.68… Connected to www.google.com. Escape character is ‘^]’. or $ nc -z -v -w5 www.google.com 80 Connection to www.google.com […]

Setting Ubuntu hostname as offered by DHCP server

A DHCP server might be setup in such a way that it offers a hostname to its clients. By default, the Ubuntu hostname is set during installation and it disregards the one in the DHCP lease, but we can change this behaviour. Create a file in the /etc/dhcp/dhclient-exit-hooks.d/ directory, for example /etc/dhcp/dhclient-exit-hooks.d/sethostname and give it […]

Android mobile network settings for Vodafone business in the Netherlands

The following settings are needed for using the Vodafone business mobile network in the Netherlands with an Android phone: Name Choose one yourself, e.g. Vodafone Business Android APN office.vodafone.nl Proxy not set Port not set Username vodafone Password vodafone Server not set MMSC http://mmsc.mms.vodafone.nl MMS proxy 192.168.251.150 MMS port 8799 MCC 204 MNC 04 Authentication […]

Using the pipe backend in PowerDNS

PowerDNS is a Domain Name System (DNS) server with a lot of different possible backends, such as MySQL, PostgreSQL, LDAP, BIND zone files and a Unix pipe backend. In this article we will look at the pipe backend which is passed the DNS request by PowerDNS through standard input (stdin) and must reply through standard […]

Ubuntu 12.04 network configuration

The network configuration of Ubuntu 12.04 has changed a bit, at least the server edition, haven’t checked the desktop version. The file /etc/network/interfaces contains a few directives that tell Ubuntu how to configure the network interfaces. There are basically two choices: dynamic configuration (through a DHCP client) or static configuration. DHCP is quite simple: auto […]

Programming the Arduino ethernet shield

The Arduino is an open-source electronics prototyping platform based on flexible, easy-to-use hardware and software. It features an IDE that allows you to program the Arduino using a standard USB cable. Several shields exist that extend the functionality of the standard Arduino platform. In the picture above the Arduino is shown on the left and […]

Enable SSL in Apache

To enable SSL in Apache, we need to perform some steps. We start by generating a key for our server: openssl genrsa -out server.key 4096 Then we generate a Certificate Signing Request (CSR) based on this key: openssl req -new -key server.key -out server.csr Make sure that you enter a valid value for Common Name […]

Configuring Postfix to use a smarthost

Some companies and ISP’s do not allow you to send mail from your machine directly, but force you to use their smarthost. In the Postfix SMTP server we can accomplish this by editing the file /etc/postfix/main.cf: relayhost = smarthost.example.org We also have to tell Postfix to which domains it may send mail. We do this […]

Installing Ganglia on CentOS

In this article we will install the Ganglia monitoring system on a set of machines running CentOS. There are two kinds of machines involved: The meta node: one machine that receives all measurements and presents it to a client through a website. The monitoring nodes: machines that run only the monitoring daemon and send the […]