Teach apt-get not to use IPv6 addresses

Create a file in /etc/apt/apt.conf.d/ starting with 90 or higher.
Example /etc/apt/apt.conf.d/90ipv6only

Put inside the following:

Acquire::ForceIPv4 "true"; 

and the do apt-get update.

This works on Debian Jessie/Devuan Jessie.

Java 1.7.x on Debian Squeeze manual install

Recently Oracle made changes in java package license and it will be no longer shipped with Debian. Debian people said that this prevents even updates for old packages to be released. For more information read here: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=649594

Here is solution how to install newer java packages manually on Debian Squeeze.

Download the package and unpack it in /usr/lib/jvm/

# zcat jdk-7u71-linux-i586.tar.gz|tar xvf -
# mv jdk1.7.0_71 /usr/lib/jvm/java-1.7
# chown -R root:root /usr/lib/jvm/java-1.7/*

Now use update-alternatives script to add it to /etc/alternatives

# update-alternatives --install "/usr/bin/java" "java" "/usr/lib/jvm/java-1.7/bin/java" 1
# update-alternatives --install "/usr/bin/javaws" "javaws" "/usr/lib/jvm/java-1.7/bin/javaws" 1
# update-alternatives --install "/usr/bin/javac" "javac" "/usr/lib/jvm/java-1.7/bin/javac" 1

Now set the new java binaries as default (choose the one with the right path):

# update-alternatives --config java
# update-alternatives --config javac
# update-alternatives --config javaws

Roundcube missing contacts after changing IP address of the server.

If you have working installation of Roundcube and for some reason change your IP address the result is missing address book entries of all users.

If in the configuration file config/main.inc.php the line:
$rcmail_config['default_host'] = '10.10.200.1';
is changed to some other IP address (for instance 192.168.10.1) the result is missing address book entries.

In fact entries are not missing but Rouncube shows only enties for the users with current 'default_host' IP address. This means that you have two entries for each users with different 'default_host' field. How to fix it?

First delete all newly created entries with the new default_host:
old: 10.10.200.1, new: 192.168.10.1.

# mysql -u roundcubeuser -proundcubepass
mysql> use roundcube
mysql> delete from users where mail_host='192.168.10.1';
Query OK, 60 rows affected (0.07 sec)

Now change all remained entries with the new default_host:

mysql> update users set mail_host='192.168.10.1' where mail_host='10.10.200.1';
Query OK, 105 rows affected (0.08 sec)
Rows matched: 105  Changed: 105  Warnings: 0

Now you have your addressbook back.