Computing

Computers and information management topics

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Category: Computing
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At installation Dovecot creates a self-signed certificate that will expire in one year. Often your server installation will be in place longer than this. So, one solution is to create a new certificate that expires in 5 years. To do so follow these instructions.

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Category: Computing
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Here's a few methods to determine useful information regarding install packages, files and applications on a Ubuntu Linux system.

List installed software: dpkg -l ... or ... dpkg --get-selections

Find the package(s) that include a specific file: dpkg -S <filename>
Example: dpkg -S top

List files installed from a package: dpkg -L <packagename>

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Category: Computing
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Most Adobe Flash applications that have a fullscreen mode will exit back to their original in-webpage state when the fullscreen window looses the focus (or is not the active window). This is fine on a single monitor setup but a real pain on a dual or multi-monitor system. Often the user would like to watch a Flash based movie on one monitor (e.g., Youtube) and continue working (e.g., browse the web) on another.

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Category: Computing
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If the network hardware or virtual environment (NIC) changes mac number Ubuntu will reserve the prevously used device name and assign the next higher device number to the "new" hardware.

For example, a machine with one NIC assigned eth0 changes the NIC hardware. On the next reboot, Ubuntu will reserve eth0 for the missing hardware and assign the new NIC as eth1.

To fix this and reset Ubuntu's memory so that the new hardware is assigned eth0, remove the file /etc/udev/rules.d/70-persistent-net.rules where the assignments are recorded.

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Category: Computing
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These are specified in RFC1597 and are as follows:

Reserved Private Network Allocations
Network Class  Netmask  Network Address 
A 255.0.0.0 10.0.0.0 - 10.255.255.255
B 255.255.0.0 172.16.0.0 - 172.31.255.255
C 255.255.255.0 192.168.0.0 - 192.168.255.255