Howto articles

Last change: 2025-01-06

Nginx can be configured to rate limit HTTP requests based on the IP address of the client. Learn how to set it up and tune it to your needs.

Last change: 2025-01-08

Dig is one of the primary tools when it comes to DNS. Resolve names, perform queries, troubleshooting any issues related to DNS. It's always DNS!

Last change: 2025-01-06

Nginx can be configured to block all HTTP requests of clients that don't offer to do a compressed data transfer, saving bandwidth and energy.

Last change: 2025-01-06

Linux has multiple tools to process text files, including to search through files and filter out all unique words. Here is how to combine a few commands.

Last change: 2025-01-06

Looking for all DNS requests made on a Linux system? Tools like dnstop, firejail, and tcpdump can help to find what is being queried.

Last change: 2025-01-06

Cheat sheet for using the pacman package manager on Linux systems, including common tasks that are to be performed with pacman.

Last change: 2025-01-06

Linux hardening security guides collected in one area, covering systems like AlmaLinux, Arch, Debian, Fedora, Ubuntu, and others.

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Services that are controlled with systemd can be reloaded or restarted depending on their configuration. Use systemctl to perform the related restart tasks.

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Systemd units can be enabled or disabled based on multiple factors, such as meeting specific dependencies. Learn how to see if a systemd service is enabled.

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Systemd units can be configured to contain environment variables and passed along to the underlying application. Learn how to configure this unit setting.

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Everything related to hardware in one place. From the basics of querying hardware information, up to securing physical access and limiting hardware devices.

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This is the troubleshooting area for Linux software with focus on software issues, troubleshooting and resolving them.

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SSH logs authentication attempts, but where? Find your SSH log file with these tips, such as in /var/log/auth.log or in the systemd journal.

Last change: 2025-01-06

The apt package manager can be used to download a package file without actually installing it. See how the download subcommand is used to achieve this.

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A healthy service should not have configuration issues. Perform a configuration test of the SSH daemon (sshd) by first running it using the '-t' option.

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Learn how to see the dependencies of a package that is to be installed or already installed on the system using the apt package manager.

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Learn how to remove previously installed packages on a Linux system using the apt package manager, such as Debian and Ubuntu.

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Learn why and how packages may become unnecessary on Linux and how to remove them with the apt package manager on systems like Debian and Ubuntu.

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Got a busy Linux systems and wondering what the culprit is? Learn how to monitor them and focus on disk activity with tools like iotop, sar, vmstat, or iostat.

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The file command is a powerful tool for Linux users. Learn how to see the file type of normal and special files on a Linux system.

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File systems on Linux store a lot more than just the data itself. Learn how to see the size of a file on Linux systems using the ls or stat command.

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Learn how to sort the output of the ls command and list a directory contents by its modification time. Here is which options to use.

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Learn how to load and use your SSH key together with a SSH agent. This frequently asked question will explain the usage of ssh-add and ssh-agent.

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Collection of predefined hardening profiles for systemd that can be used to secure your applications. With detailed explanation of the unit settings.

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Systemd version 256 introduced the run0 command to run privileged commands. Learn how to get everything out of run0 tool and replace sudo.

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Linux has a wide range of tools to do data processing and text manipulation. Learn how to remove trailing whitespace from a file using the sed command.

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Learn how to insert a line of text at the beginning of a file using the sed command. Great to automate repeating tasks and do data processing.

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Frequently asked questions about data and text processing are covered in this section with focus on Linux tools and systems.

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The systemctl command can be used to show the memory usage of a service managed by systemd. Use the subcommand 'status' to find the details about a unit.

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Linux systems using systemd can use the systemctl command to show the all applied unit settings. This can be used on units like a service.

Last change: 2025-01-06

Systemd units have their own configuration file. The systemctl 'edit' command can be used to override settings of a systemd unit, including services.

Last change: 2025-01-07

Secure your nginx service by using security features provided by systemd. We have a look at the available options that systemd units can offer.

Last change: 2025-01-06

Control groups allocate resources to a set of processes. Learn how to find the control group (cgroup) of a process by using /proc, pidof, or ps.

Last change: 2025-01-06

Want to see the control group in the output of the ps command? Here is how to tune your command options to include that.

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Linux systems running systemd can use the timedatectl command to show time synchronization details. Learn how to use it, including its subcommands.

Last change: 2025-01-06

The agent forwarding feature in SSH allows using your local SSH agent to be reached through an existing SSH connection. Learn when and how to use it.

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The OpenSSH agent helps with authentication by making SSH keys available. Learn how to start the SSH agent when it is not running on your Linux system.

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The SSH agent is a helper utility to temporarily store private keys when using public key authentication. Learn more about how this helps during daily tasks.

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The SSH agent can be used to simplify authentication. As that is not always preferred behavior, we can disable the SSH agent when authenticating.

Last change: 2025-01-06

On Linux systems such as Arch Linux, pacman is the default package manager. Query the pacman package manager to show all installed packages.

Last change: 2025-01-06

Learn how to stop all processes of a single user using the killall command. To make this work, use the --user option and specify the username.

Last change: 2025-01-06

OpenSSH performs a host authenticity check when connecting to a system. Learn how to disable the check with the SSH option StrictHostKeyChecking.

Last change: 2025-01-06

Learn about SSH escape sequences and how they can help with terminating a SSH connection that does not respond to CTRL+C.

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While protecting SSH keys is typically advised, it is not always feasible in automated processes. Learn how to remove the password or passphrase from a SSH key.

Last change: 2025-01-06

The SSH agent can load stored SSH keys into memory for authentication purposes. Use the ss-add command to show the available SSH keys that are loaded.

Last change: 2025-01-06

Frequently asked questions about SSH, such as SSH keys, configuration, and usage.

Last change: 2025-01-06

A zombie process, or defunct process, has completed execution, but has still an entry in the process table. Learn more about a zombie process on Linux.

Last change: 2025-01-06

How to kill a zombie process on Linux if it no longer responds to kill -9? Learn about zombie processes, including a few last steps that you can try.

Last change: 2025-01-06

When running a Linux system, you may need to find the process ID (PID) and process name. On Linux we can do this with the help of the pgrep command.

Last change: 2025-01-06

Each process on Linux has its own number. Discover this number is called the process ID (PID). Learn how to find the PID for a running process by name.

Last change: 2025-01-06

Linux administrators can interact in multiple ways with running processes. Learn how to find and stop a running process on Linux by searching for its name.

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Frequently asked questions about running processes on a Linux systems, such as starting and stopping processes, query information, and monitoring them.

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Show IP address information on Linux with the help of the ip command. Learn which subcommands to use to query the relevant details.

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Show the IP address of your internet connection using the dig or the curl command. Learn which options can be used to find out this information.

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Find the active DNS server being used by reviewing the network configuration, including common commands to query this information.

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Use the find command to search for any files on Linux that are writable. To make this work, the -perm option of find can be used.

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The cheat sheet for the apt package manager to cover the most used options. Learn how to get more out of the apt command.

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Disks will eventually fill up. Learn how to quickly see the size of a directory or folder on Linux systems using the du command.

Last change: 2025-01-06

Files starting with a dot are usually hidden on Linux. Learn how to see any hidden files on the command line or in the terminal using the ls command.

Last change: 2025-01-06

Learn how to see files smaller or bigger than a specific defined size on Linux, using the du command. Or use the find command to achieve a similar result.

Last change: 2025-01-06

Linux filesystems typically store file modification timestamps. Learn how to find the last modification time of a file or subdirectory in a specified directory.

Last change: 2025-01-06

Linux file systems use inodes, unique references to link to a file or directory. Learn how to see inode usage on a Linux file system or mount point.

Last change: 2025-01-06

Learn how to see used and remaining disk space on Linux systems by gathering the statistics of file systems and mount points using the df command.

Last change: 2025-01-06

Symbolic links may point to a directory or a file. Learn how to use the find command to discover symbolic links that refer to a directory.

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Learn how to compare two directories on a Linux systems and see their differences between both or what files they are having in common.

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Tips and tricks for getting everything out of the Linux command-line or terminal. Learn about commands and how to combine them in a smart way.

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Linux has in-depth details, including about network connections. Show the number of open connections using the ss command on Linux.

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Linux has in-depth process information. Learn more about processes, such as when a process was started, using the ps tool.

Last change: 2025-01-06

There are multiple ways to see when a Linux system was started, such as using the uptime command, but also with commands like ps.

Last change: 2025-01-06

Frequently asked questions about system administration on Linux, the system state, how to perform common tasks, and troubleshooting issues.

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Show the bandwidth usage and active connections by using the iftop tool on Linux. Learn how to use the tool to quickly find out this information.

Last change: 2025-01-06

Linux with systemd might doing DNS resolving using its resolver daemon. Learn how to inspect and clear the DNS cache when using the systemd resolver daemon.

Last change: 2025-01-06

Show counters related to the TCP connections by using the nstat command. This small utility will quickly retrieve the related statistics and display them.

Last change: 2025-01-06

Show CPU details such as architecture, vendor, caches, virtualization options, and even known CPU vulnerabilities such as Meltdown and Spectre.

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Articles and tools to troubleshoot Linux system performance issues. Learn more about the available tools and good one-liners.

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Memory pages might need to be swapped to disk if the physical memory is full. Troubleshoot Linux system performance issues with focus on swap memory.

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Get more information out of the tcpdump tool using this cheat sheet. Find everything that is going on the network and your Linux systems.

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Learn how to find the Linux distribution and version of a system. Use the right tool or file to find the relevant details.

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Everything related to managing Linux systems, from discovering what Linux distribution is running, up to full configuration and automation.

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Want to see all hardware details of a system? Then dmidecode is your friend, helping to decode all information from the SMBIOS specification.

Last change: 2025-01-06

Linux systems have a wide range of supporting utilities available. Show memory information such as memory type, the number of banks in use, and speed.

Last change: 2025-01-06

Need to delete the contents of a sensitive file on Linux? Instead of just deleting it with rm, have a look at some other options for a more secure deletion.

Last change: 2025-01-06

Linux may store the initial creation of a file. Learn how to use the stat command to find this initial creation time of a file, also known as its birth time.

Last change: 2025-01-06

All Linux cheat sheets to simplify your system administration and Linux security efforts. Something missing? Let it know.

Last change: 2025-01-06

Become a master in archiving and compressing files using the tar tool with this cheat sheet, filled with examples and commonly used options.

Last change: 2025-01-06

Frequently asked questions about the Linux kernel and kernel security.

Last change: 2025-01-06

Want to see or configure every piece of information about networking, including routing on Linux? Forget tools like netstat and learn using the ip command.

Last change: 2025-01-06

Show the network link details using the ip command to find out if a network has errors or dropped packets on a Linux system.

Last change: 2025-01-06

Use the network routing table to discover the default gateway on a Linux system. Here is how to use the ip command to achieve this

Last change: 2025-01-06

TCP or UDP ports can already be in use when starting up a service. Find out which process opened an UDP or TCP port on Linux by using the ss command.

Last change: 2025-01-06

Get information about open files on Linux using the lsof command. This cheat sheet covers many common uses for using lsof and how to use it.

Last change: 2025-01-06

Show which UDP/TCP ports are opened on a Linux system, including the related process. Use the ss tool to see more details about these sockets.

Last change: 2025-01-06

If you want to learn more about network connections on Linux, then ss is the tool to get the job done. Learn how to use it with this cheat sheet.

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Frequently asked questions about networking, such as DNS, IP configuration, TCP/UDP details, and more.

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Learn how to query the Time To Live (TTL) for a DNS record by using the dig tool on a Linux systems, including any relevant options.

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Query the package manager to show installed packages on Ubuntu systems including version details. This can be done with the dpkg command and --list option.

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Frequently asked questions about software and in particular the package manager. Learn how to install packages, query package versions, and more.

Last change: 2025-01-06

Learn how to show installed packages on Linux systems. This overview covers common package managers including those for AlmaLinux, Debian, openSUSE, and Ubuntu.

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Everything related to package managers like apt, dnf, yum, and zypper. Learn how to use the tools to install and configure packages.

Last change: 2025-01-06

Everything related to software, including package managers, building software packages, and more.

Last change: 2025-01-06

Retrieve device information from USB hubs and devices on Linux using the lsusb command. Learn how to use the command and its output.

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Show the available hard disks in a system by using the right Linux tool. There are multiple options to pick, so let's have a look.

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Show more detailed information about the available hard disks in the system. Specifications like speed, serial number, firmware, and other details.

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The BIOS details can be displayed from within Linux itself. Learn how to query these details and where to find more information.

Last change: 2025-01-06

Frequently asked questions about hardware information on Linux systems, such as BIOS details, hard disks, USB devices, memory, and other details.

Last change: 2025-01-06

Get more out of the du utility with this cheat sheet. Use it as a reference to find often-used options or those that come handy in time.

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Systemd is a system and service manager for Linux systems. This section covers the basics like the different units tips up to advanced troubleshooting.

Last change: 2025-01-06

Find the biggest directories and files on disk by using the du command. The output can be sorted using numeric values to find the biggest entries.

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Want to find all masked unit files on a Linux system running systemd? In this article we show how to do this with systemctl and query those units.

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Limit the output from journalctl by defining the number of lines you want to see by using the '-n' option, optionally with the service itself.

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Want to disable a service or specific systemd unit? Use the systemctl command to configure units and disable it on boot or completely.

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Systemd can start and enable a unit, such as a service at the same time. Learn how to use systemctl more efficiently to achieve this this action.

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Want to check the system for failed systemd units? In this article we show how to do this with systemctl and query the units with a failure state.

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Frequently asked questions about systemd, systemctl, and journalctl. Learn by practical examples how to use these tools.

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Frequently asked questions about file systems, file permissions, directories and files.

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The find utility is probably the best tool to find files on your system, but it has some learning curve. We help you to achieve that with this cheat sheet.

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Increase your system administration skills with this systemd cheat sheet, including how to configure and monitor systemd units.

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Want to test your web server and see if static files are properly cached? Curl can help and with some scripting even automate the task for you.

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Learn how to get every piece of information from systemd units, such as services and timers, including its configuration and status.

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Learn how to get every piece of information from systemd journals with the journalctl command. This cheat sheet will help you with the task.

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Want to improve caching on your nginx web server? Learn how to set the Expires header and enhance your nginx configuration.

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This curl cheat sheet contains commands and examples of common tasks that can be performed with curl. Covering a wide range of curl options, tricks, and tips.

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Learn how to secure your nginx configuration with this hardening guide. It includes examples and tips to implement security measures step by step.

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Want to delete one or more characters from a variable or piped output? There are multiple ways to achieve this using standard system utilities.

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When it comes to a powerful tools on Linux, AWK is definitely one to know. This cheat sheet explains the basics and shows many useful one-liners

Last change: 2025-01-06

Want to see all configured virtual hosts on a server running nginx? Here is a method to achieve this quickly by using a default configuration option.

Last change: 2025-01-06

Nginx is flexible when it comes to what should be logged in the access.log. With the combination of a map and if-statement, this can be achieved very easily!

Last change: 2025-01-06

Searching for the installed version of OpenSSH? Here are some commands to discover what software you are running, including the related packages.

Last change: 2025-01-06

Want to rename files in bulk, but looking for a good tool that can be used on Linux? This article has your covered, with several options.

Last change: 2025-01-06

Want to determine if a Linux account has a password set or its related properties? Here are few methods to check this and the steps to perform.

Last change: 2025-01-06

Optimizing a web server and its content can be done using brotli and gzip compression. This article shows a few ways to test your website.

Last change: 2025-01-06

The strace utility is diverse and helpful in performance tuning, troubleshooting, and monitoring process activity. Get the most out of this powerful tool!