apt – install the package that contains a specific file

Sometimes a command that you execute complains about a dependency being missing on the system. From the file name in the error message it is often not possible to know exactly which package needs to be installed to resolve the … Continue reading

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Understand the basics of rrdtool to create a simple graph

rrdtool is a powerful tool to store time series data and create graphs. It is very easy to create your first simple graph. This how-to will show the quickest way to generating your first graphs while explaining the options used. rrdtool is used in … Continue reading

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Increase the size of a LUKS encrypted partition

Even encrypted discs or partitions sometimes need to have their size increased. A LUKS encrypted volume consists of different layers which all need to be resized. To resize an encrypted volume, multiple steps have to be performed to use the additional … Continue reading

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Update to PHP 5.6 on CentOS 6 using remi repository

With CentOS being a conservative distribution, security patches are still applied to CentOS 6, but no new versions are available. When running some websites – like Virtualmin – on CentOS 6, the old PHP version 5.3.3 can cause problems. Updating to a newer … Continue reading

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Permanently reject a specific email sender address using postfix

Postfix generally accepts all sender addresses. It might be needed in some rare cases to reject one sender addresses for some reason. With postfix, there is the possibility to use the “check_sender_access” to set individual actions per sender address. For the … Continue reading

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Certificate Transparency and unauthorized certificates

I own a domain which was bought a few months back which is managed by CloudFlare’s service in DNS-only mode. As I intended to only use CloudFlare’s DNS service, I disabled every option except the DNS related features. You can imagin the surprise to see certificates issued for my domain without my knowledge. Continue reading

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How to get scrollbar arrows in Linux Mint 17

Linux Mint is missing the scrollbar arrow buttons at the end of the scrollbars. There are situations in which those buttons can be very useful. This how-to will explain how to get them back. Sadly I could not find any … Continue reading

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Verifying SSH configuration with a scan

Managing a number of Linux servers and keeping them secure can be a challenge. Certain tools can make the life of an admin a lot easier. To ensure an ssh daemon complies with a desired security configuration the admin can use a scanner … Continue reading

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Debug SSH Connection issue in key exchange

Securing a server means hardening the SSH server settings, but doing so can also cause issues with ssh clients. Finding the cipher or algorithm causing a failled connection can be tricky. Depending on the client used, the error message might be very … Continue reading

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Automount a luks encrypted volume on system start

Linux supports encrypted volumes with luks. When a luks encrypted volume is set up during installation to be booted from, the volume is already configured and set up. When an encrypted volume is set up afterwards, the volume remains locked until … Continue reading

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