Sysadmin

GitLab : fix "cgroups: cgroup mountpoint does not exist: unknown"

GitLab Sysadmin Docker

If you use GitLab pipelines to build Docker image, you may encounter the error "cgroups: cgroup mountpoint does not exist: unknown". Here is how to fix...

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Benchmark Linux systems with sysbench

Linux Sysadmin

In this blog post, I will show how to use sysbench to test the CPU, memory and storage performance of a Linux system. I also had the chance to access some diverse hardware (laptop, desktop, servers). So I'll also give some results for you to compare with.

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Build a kernel, initramfs and Busybox to create your own micro-Linux

Linux Sysadmin

A regular Linux user will probably never have to compile it's own Linux kernel. But doing so is actually a great way to discover the features and working of the Linux kernel. So in this blog post we will guide you to compile a small kernel, create a minimal root filesystem that fits into memory, and finally create a micro-Linux system based on Busybox...

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Network boot for UEFI devices with iPXE

Sysadmin Linux

In a previous blog post, we have seen how PXE network boot works, and how to implement PXE boot for devices with a (classical) BIOS. For this purpose, we used SYSLINUX/PXELINUX. However, SYSLINUX/PXELINUX is usually not working well with modern UEFI devices. Hence in this blog post, we will show how to use iPXE to implement network boot for UEFI devices.

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Understand and implement PXE network boot

Linux Sysadmin

PXE is a powerful system that allows to boot a system from the network. The applications are numerous : install a system from the network, create diskless or kiosk systems. But the system is pretty complex! In this blog post we will explain how network booting works, and show an example to allow interactive installation of Ubuntu 22.04 server from the network...

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Create a handler for opening special URLs like 'ssh://'

Linux Sysadmin

Sometimes when using a web application you may encounter a special URL that does not start with http or https, like ssh://192.168.0.123 for example. On a mobile device, your phone will usually open the appropriate application to handle this URL. Here is how to achieve the same on a Linux computer.

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Velociraptor : hunt malwares as a pack

Forensics Sysadmin Linux

Velociraptor is a digital forensic and incident response tool that allows to collect information on multiple endpoints at once, and easily analyze the collected data using Notebooks and a query language (called Velociraptor Query Language, VQL), which is very similar to SQL. This makes Velociraptor a valuable tool for threat hunting over a large network.

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Explore the SAM hive with Regedit (and Sysinternals)

Windows Sysadmin Forensics

The Windows Registry is a kind of database that stores a lot of important configuration parameters for Windows and installed applications. The specific of this database is that the data is actually stored in different files called hives. One of these is the SAM (Security Account Manager) hive, which stores, among others, user passwords. Let's explore this hive a little..

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Install Sysinternals

Windows Sysadmin Forensics

Sysinternals is a collection of powerful utilities for Windows. They can be used by system administrators to perform local or remote system administration, and also by analysts to perform some forensics tasks. The tools were originally developed by Mark Russinovich, and are now maintained by Microsoft. Here is how to install them...

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Install a recent kernel on Ubuntu

Sysadmin Linux

Even if you are regularly updating your Ubuntu system, you may be running a relatively old version of the kernel. At the time of writing (28 August 2023), Ubuntu 22.04 ships with a kernel numbered 5.15.0, which was release on 31 October 2021. This is more than 2 years ago...

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How to detect filtered (and opened) outgoing ports on a network?

Sysadmin Offensive Security

Sometimes you want to access services running on unusual ports, like a SSH server running on port 2222 for example. If connection fails, how can we detect the outgoing ports that are filtered or open on the network?

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Filter USB devices with udev (and some PHP code)

Sysadmin PHP

USB devices can be a liability : they can be used to exfiltrate data from a computer or server, to plug a hardware keylogger, or to plant a malware. Hence on a managed computer, USB devices should be filtered and whitelisted. In this blog post we show how this can be achieved thanks to udev, and some PHP code.

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