Howto
Hardware
Everything related to hardware in one place. From the basics of querying hardware information, up to securing physical access and limiting hardware devices.
How to monitor disk activity (I/O) on Linux
Learn how to monitor a Linux system and focus on disk activity with tools like iotop, sar, vmstat, or iostat.
How to see the file type on Linux
Learn how to see the file type of normal and special files on a Linux system by using the file command.
How to see the size of a file
Learn how to see the size of a file on Linux systems using the ls or stat command.
How to display directory contents sorted by modification time
Learn how to sort the output of the ls command to list a directory contents by its modification time.
How to add a SSH key to the SSH agent
Learn how to load and use your SSH key together with a SSH agent.
Hardening profiles for systemd
Hardening profiles for systemd that can be used to secure your applications.
Run0 cheat sheet
Learn how to get everything out of the run0 tool to increase your privilege level.
How to remove trailing whitespace from a file
Learn how to remove trailing whitespace from a file using the sed command.
How to insert a line at the beginning of a file
Learn how to insert a line of text at the beginning of a file using the sed command.
Data processing: Frequently Asked Questions
Frequently asked questions about data and text processing.
How to see memory usage of a service with systemctl?
The systemctl command can be used to show the memory usage of a service managed by systemd.
How to see the active settings of a systemd unit
The systemctl command can be used to show the settings of a systemd unit, like a service.
How to override the settings of a systemd unit
The systemctl command can be used to override settings of a systemd unit, like a service.
Hardening nginx with systemd security features
Secure your nginx service by using security features provided by systemd.
How to see the cgroup of a process
Learn how to find the control group (cgroup) of a process by using /proc, pidof, or ps.
How to see cgroup in ps output
Want to see the control group in the output of the ps command? Here is how to tune your command options to include that.
How to see the time synchronization details with timedatectl
Show time synchronization details with the systemd timedatectl command and related subcommands.
What is SSH agent forwarding?
Learn more about the SSH agent forwarding feature and what problems it tries to resolve.
How to start the SSH agent?
When the SSH agent is not running, how can you start it? In this article we will have a look at the options.
What is the purpose of the SSH agent?
What is the purpose of the SSH agent and when to use it?
How to disable the usage of the SSH agent
Learn how to disable the usage of the SSH agent when authenticating.
How to show all installed packages with pacman
Query the pacman package manager on systems like Arch to show installed packages.
How to stop all processes of a single user
Learn how to stop all processes of a single user using the killall command.
How to disable the SSH host key check?
Learn how to disable the SSH check of host authenticity and key fingerprint with ssh option StrictHostKeyChecking.
How to terminate a SSH connection that does not respond to CTRL+C
Learn about SSH escape sequences and how they can help with terminating a SSH connection that does not respond to CTRL+C.
How to remove the passphrase from a SSH key
Remove the password or passphrase from a SSH key using the ssh-keygen command.
How to see the available SSH keys in the OpenSSH authentication agent
Show the available SSH keys that are loaded in the SSH authentication agent.
SSH: Frequently Asked Questions
Frequently asked questions about SSH, such as SSH keys, configuration, and usage.
What is a zombie process?
What is a zombie process on Linux and how to deal with it? In this article we will have a look at the details.
How to kill a zombie process
How to kill a zombie process if it does not respond to kill -9? Here are a few last steps that you can try.
How to show a running process name and its process ID (PID)
Find the process ID (PID) and process name on Linux with the help of the pgrep command.
How to find all process IDs by its process name
Discover the process ID (PID) on Linux for a running process by searching for its process name.
How to kill a running process by its name
Find and stop a running process on Linux by searching for its name using the killall or pkill command.
Processes: Frequently Asked Questions
Frequently asked questions about start and stop processes, discover information, and monitoring them.
How to see the the network IP address of your system
Show the IP address of your system with the help of the ip command.
How to see the IP address of your internet connection
Show the IP address of your internet connection using the dig command.
How to see which DNS server is used
Find the active DNS server being used by reviewing the network configuration, including common commands to query this information.
How to find writable files
Learn how to the use the find command to find any files that are writable.
Apt cheat sheet
The package manager apt gots much more options than one could think. In this cheat sheet they get uncovered.
How to see the size of a directory
Learn how to see the size of a directory or folder on Linux systems using the du command.
How to see hidden files
Learn how to see any hidden files on the command line or in the terminal using the ls command.
How to see files great than a specific size
Learn how to see files smaller or bigger than a specific defined size on Linux, using the du command.
How to find when the last modification happened in a directory
Learn how to find the last modification time of a file or subdirectory in a specified directory on Linux.
How to see inode usage
Learn how to see inode usage on a Linux file system or mount point.
How to see used and free disk space
Learn how to see used and disk space of file systems or mount point on Linux systems.
How to find symbolic links that point to a directory
Learn how to use the find command to discover symbolic links that refer to a directory.
How to compare two directories and find the differences
Learn how to compare two directories and see their differences or what files they are having in common.
Command-line
Tips and tricks for getting everything out of the Linux command-line or terminal.
How to see the number of open connections on Linux
Show the number of open connections using the ss command on Linux.
How to see when a process was started
Show process details to learn more about when a process was started using the ps tool.
How to see when the system was started (uptime)
When did a system start? Learn how to query the boot time (uptime) of a system using commands like uptime and ps.
System administration: Frequently Asked Questions
Frequently asked questions about system administration, system state, and how to perform common tasks.
How to see active connections and bandwidth usage on Linux
Show actual bandwidth usage and active connections using the iftop tool on Linux.
Show to clear the DNS cache with systemd
Learn how to inspect and clear the DNS cache when using the systemd resolver daemon.
How to show network TCP statistics and counters
Show counters related to the TCP connections by using the nstat command. This small utility will quickly retrieve the related statistics and display them.
How to see CPU details
Show CPU details such as architecture, vendor, caches, virtualization options, and even known CPU vulnerabilities such as Meltdown and Spectre.
System performance
Articles and tools to troubleshoot Linux system performance issues.
Swap memory information
Articles and tools to troubleshoot Linux system performance issues with focus on swap memory and its usage.
Tcpdump cheat sheet
Get more information out of the tcpdump tool using this cheat sheet. Find everything that is going on the network and your Linux systems.
Methods to find the Linux distribution and version
Learn how to find the Linux distribution and version of a system. Use the right tool or file to find the relevant details.
System administration
Everything related to managing Linux systems, from discovering what Linux distribution is running, up to full configuration and automation.
Dmidecode cheat sheet
Want to see all hardware details of a system? Then dmidecode is your friend, helping to decode all information from the SMBIOS specification.
How to see memory information such as type and speed
Show memory information and details such as the number of banks in use, the memory type and speed.
How to securely delete a file and its contents
Need to delete the contents of a sensitive file? Instead of just deleting it with rm, look at this option first.
How to see the creation date of a file
Learn how to use the stat command to find the initial creation time of a file, also known as its birth time.
Cheat sheets
All cheat sheets to simplify your system administration and Linux security activities. Something missing? Let it know.
Tar cheat sheet
Become a master in archiving and compressing files using the tar tool with this cheat sheet.
Kernel: Frequently Asked Questions
Frequently asked questions about the Linux kernel and kernel security.
Ip cheat sheet
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.
How to see errors and dropped packets on a network interface on Linux
Show the network link details using the ip command to find out if a network has errors or dropped packets on a Linux system.
How to see the default gateway on Linux
Show the network routing table to discover the default gateway used on a Linux system.
How to see which process is using a port
Show which process is already opened an UDP or TCP port on Linux by using the ss command.
Lsof cheat sheet
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.
How to see open ports on Linux
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.
Ss cheat sheet
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.
Networking: Frequently Asked Questions
Frequently asked questions about networking, such as DNS, IP configuration, TCP/UDP details, and more.
How to see the TTL value of a DNS record
Learn how to query the Time To Live (TTL) for a DNS record by using the dig tool.
How to show all installed packages on Ubuntu
Query the package manager to show installed packages on Ubuntu systems including version details.
Package manager: Frequently Asked Questions
Frequently asked questions about software, such as package manager, package versions, and how to configure them.
List installed packages on a Linux system
Learn how to show all installed packages on Linux systems including AlmaLinux, Debian, OpenSUSE, and Ubuntu.
Package manager
Everything related to package managers like apt, dnf, yum, and zypper. Learn how to use the tools to install and configure packages.
Software
Everything related to software, including package managers, building software packages, and more.
How to list all USB devices
Retrieve device information from USB hubs and devices using the lsusb command.
How to see the available hard disks
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.
How to see hard disk specifications and details
Show more detailed information about the available hard disks in the system. Specifications like speed, serial number, firmware, and other details.
How to see BIOS details
Show bios details from within a Linux system. Learn how to query these details and where to find more information.
Hardware: Frequently Asked Questions
Frequently asked questions about hardware information such as bios, USB devices, memory, and other details.
Du cheat sheet
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.
Systemd
Everything related to systemd in one place. From the basics like the different units tips, up to advanced troubleshooting.
How to find the biggest directories on disk
Find the biggest directories and files on disk by using the du command.
How to see all masked units with systemctl
Want to find all masked unit files? In this article we show how to do this with systemctl and query those units.
How to see the last X lines with journalctl
Limit the output from journalctl by defining the number of lines you want to see.
How to disable a systemd unit with systemctl
Want to disable a service or specific systemd unit? Use systemctl to configure units and disable it on boot or completely.
How to start and enable a unit with systemctl
Combine the start and enable command when using systemctl to get a unit like a service started at boot and right away.
How to show failed units with systemctl
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.
Systemd: Frequently Asked Questions
Frequently asked questions about systemd, systemctl, and journalctl. Learn by pratical examples how to use these tools.
File systems: Frequently Asked Questions
Frequently asked questions about file systems, file permissions, directories and files.
Find cheat sheet
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.
Systemd cheat sheet
Increase your system administration skills with this systemd cheat sheet, including how to configure and monitor systemd units.
Test web server caching with curl
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.
Systemctl cheat sheet
Learn how to get every piece of information from systemd units, such as services and timers, including its configuration and status.
Journalctl cheat sheet
Learn how to get every piece of information from systemd journals with the journalctl command. This cheat sheet will help you with the task.
Adding the Expires header to improve caching static content in nginx
Want to improve caching on your nginx web server? Learn how to set the Expires header and enhance your nginx configuration.
Curl cheat sheet
One of the best HTTP clients is the open source tool curl. With ongoing development and new updates, it is worth getting everything out of this powerful tool!
Nginx security hardening guide
Learn how to secure your nginx configuration with this hardening guide. It includes examples and tips to implement security measures step by step.
Strip one or more characters from a variable or output
Want to delete one or more characters from a variable or piped output? There are multiple ways to achieve this using standard system utilities.
AWK cheat sheet
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
How to see all virtual hosts in nginx
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.
How to log only some requests to a log file in nginx
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!
How to find the OpenSSH version
Searching for the installed version of OpenSSH? Here are some commands to discover what software you are running.
Linux tools to bulk rename files
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.
How to test if an account has a password set?
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.
How to test if a website supports Brotli or Gzip compression
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.
Strace cheat sheet
The strace utility is diverse and helpful in performance tuning, troubleshooting, and monitoring process activity. Get the most out of this powerful tool!