Troubleshooting a full /boot partition on Ubuntu

A regular issue with systems running Ubuntu is that may fill up the /boot partition. After trying several options, we found a way to do this in three steps. And opposed to other solutions, there is no manual moving of files needed. The error: Unmet dependencies Typically you will discover if the unmet dependencies error shows up. For some reason, one package depends on the other. This typically happens over night, especially if you use a tool like unattended-upgrade for […]

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Understanding what runs on your Linux system (and why)

Linux processes and daemons Each Linux system has a bunch of processes running. Most of these processes might be familiar to you if you regularly use a command like ps or top to display them. Processes may look like just an item in a list. They are actually complicated pieces of code that are tamed by a memory manager. To truly understand how your system is running, knowledge of process (or memory) management is of great help. So let’s make […]

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Configure the time zone (TZ) on Linux systems

Linux Time Zone Configuration Having the right time set on a Linux system is important for the synchronization of data, forensics, and troubleshooting. Having the right time zone is the next step. We will have a look on how to check and configure the time zone on Linux systems. See current time zone Most new Linux distributions use systemd now. By using the timedatectl command we can quickly see the existing time information, including the time zone. timedatectl For Linux, there […]

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How to see the version of Oracle Linux

Determine Oracle Linux version Oracle Linux is based on Red Hat Enterprise Linux. At first, it may be confusing to determine what specific operating system is running. This is because both have the /etc/redhat-release file. If that file exists, use the cat command to display the contents. Next step is to determine if there is a /etc/oracle-release file as well. If so, then you can be sure that Oracle Linux is running. cat /etc/oracle-release Sample output might be: Oracle Linux Server release […]

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Linux Security Guide (extended version)

Linux Security Guide (extended version) With so many articles about Linux security on the internet, you may feel overwhelmed by how to properly secure your Linux systems. With this guide, we walk through different steps, tools, and resources. The main goal is to have you make an educated choice on what security defenses to implement on Linux. For this reason, this article won’t show any specific configuration values, as it would implicate a possible best value. Instead, related articles and […]

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Discover to which package a file belongs to

Related Packages and Files Sometimes you want to know the related package of a file, before installation, or when it is already there. This is of great help during system hardening or general system cleanups. In this article we have a look at several ways to determine the relationships between files and the package they belong to. We have gathered this information for multiple Linux distributions. CentOS, Fedora, RHEL Show files for RPM packages rpm -qlp /path/to/file.rpm Show files for packages on […]

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Examples for daily usage of the grep command

Using the Grep command by example The grep command is one of the oldest tools for Linux and other platforms. Actually, it is much older than Linux, as is written by Ken Thompson more than 40 years ago. The name grep stands for “globally regular expression print”. This name comes from its predecessor ed and the specific mode in which you would globally search, using a regular expression, and print the output. The related command was “g/re/p”. Enough history, it is […]

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How to solve an expired key (KEYEXPIRED) with apt

Updating expired keys on Debian and Ubuntu Software updates and package management is easy with systems based on Debian or Ubuntu. Just apt-get update (or apt update) and run an upgrade. But sometimes you may encounter the following situation: a KEYEXPIRED message. root# apt-get update && apt-get upgrade Get:1 http://security.ubuntu.com/ubuntu xenial-security InRelease [94.5 kB] Hit:2 http://nl.archive.ubuntu.com/ubuntu xenial InRelease Get:3 http://nl.archive.ubuntu.com/ubuntu xenial-updates InRelease [95.7 kB] Hit:4 http://nl.archive.ubuntu.com/ubuntu xenial-backports InRelease Hit:5 https://packages.cisofy.com/community/lynis/deb stable InRelease Get:6 http://nl.archive.ubuntu.com/ubuntu xenial-updates/main amd64 Packages [373 kB] Ign:7 […]

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