Faq
What is the difference between /dev/random and /dev/urandom?
Learn the difference between the Linux kernel random sources /dev/random and /dev/urandom and when to use which one.
How to clear systemd journal logs by time
Learn how to use the journalctl command to query the disk usage of the journal logs and how to clean or trim them by number, size, or age.
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 schedule a periodic task with systemd
Schedule a repeating task via systemd by using a timer. Learn how to configure and use it.
How to check if systemd is being used or active
Learn how to quickly confirm that systemd is being used as your system and service manager.
How to add a SSH key to the SSH agent
Learn how to load and use your SSH key together with a SSH agent.
How to see all enabled services with systemctl
The systemctl command can be used to show all service units and filter those that are enabled.
What does systemctl daemon-reload do?
When making changes to systemd unit files, you may need to use systemctl daemon-reload. This article explains what happens next.
How to check if 'systemctl daemon-reload' is needed
When systemd units are changed, a 'systemctl daemon-reload' might be needed. Need to know if this is the case? Let's test for that.
How to see which syscalls are part of a systemd syscall filter set
Learn how to see what syscalls are part of a particular syscall filter set in systemd.
What is the difference between systemctl disable and systemctl mask?
Want to disable a service, but wondering the difference between systemctl disable and systemctl mask? This article shows the differences between the two.
How to use systemctl edit to change a service?
Learn how to edit an existing systemd service unit with the systemctl edit command.
How to see only running services with systemctl
The systemctl command can be used to filter its output and only show all running services.
How to disable the background color of run0
Learn how to disable the change of the background color when using run0.
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.
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.
How to show the systemd machine ID
Find the machine ID that was generated by systemd.
How to see the dependencies of a systemd unit
The systemctl command has the list-dependencies option to show dependencies between units. But there are more options to query a little bit more information.
How to see the available systemd unit types
The systemctl command can be used to show all available systemd unit types.
How to see all active systemd units of one type
The systemctl command can be used to show all active systemd units of one particular type with the --type option.
How to limit the disk usage of the systemd journal
Learn how to define the maximum size that the systemd journal daemon may use for storing journals.
How to see the size of the systemd journal
Use the journalctl command to show the size of the systemd journal logs. In this article we look how journalctl vacuuming works.
How to see kernel messages with journalctl
Learn how to show all kernel events by using journalctl and filter out the kernel entries in the journal.
What is a systemd unit?
Learn more about systemd units and what they do.
How to see only recent journal entries
Learn how to filter journal entries by specifying a date or time interval.
How to see new log entries automatically with journalctl
Learn how to continuously show new log entries with journalctl like the tail -f command.
How to see logging for a specific unit or service
Limit the number of log entries from the systemd journal by filtering journalctl output by unit.
How to reload the systemd configuration
How can systemd be instructed to reload its configuration?
What is systemd?
Learn what systemd is and the main components of this system and service manager.
What is a masked systemd unit?
What does it mean when a systemd unit is masked? Learn about this state.
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.
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.
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.
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.
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.
What is a tainted kernel
Learn what it means when the Linux kernel is marked as tainted, including finding the cause.
How to find the specific cause of a tainted kernel
Learn what it means when the Linux kernel is marked as tainted and in particular the underlying cause.
Kernel: Frequently Asked Questions
Frequently asked questions about the Linux kernel and kernel security.
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.
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.
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.
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.
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.