The most important Linux commands that every user should know

The Linux system is a powerful tool that offers users tremendous flexibility and control over their working environment. However, to fully harness its potential, it is worth knowing the key commands that are essential for both beginners and advanced users. In this article, we will present and discuss the most important Linux commands that every user should know.

1. Basic Navigation Commands

  • pwd – Displays the current directory path you are in:
  • ls – Lists the contents of a directory. You can use the -l option for a detailed view or -a to show hidden files:
  • cd – Changes the directory. For example, cd /home/user will move you to the /home/user directory:
  • mkdir – Creates a new directory:
  • rmdir – Removes an empty directory:

2. File Management

  • cp – Copies files or directories:
  • mv – Moves or renames files/directories:
  • rm – Removes files or directories. Use the -r option to remove a directory with its contents:
  • touch – Creates an empty file or updates the modification time of an existing file:

3. Process Management

  • ps – Displays currently running processes. Use the -aux option to see all processes:
  • top – Displays a dynamic list of processes in real time:
  • kill – Stops a process by its ID:
  • bg and fg – Manage background and foreground processes:

4. User and Permission Management

  • sudo – Allows a command to be executed with administrator privileges:
  • chmod – Changes permissions for files/directories:
  • chown – Changes the owner of a file/directory:
  • useradd and userdel – Adds and removes users:

5. Networking and Communication

  • ping – Checks the connection with another host:
  • ifconfig – Displays information about network interfaces:
  • ssh – Connects remotely to another computer:
  • scp – Copies files over SSH:

6. Command Usage Examples

Below is an example of using several discussed commands:

  • chmod – Changes permissions for files/directories:
  • chown – Changes the owner of a file/directory:
  • useradd and userdel – Adds and removes users:

7. Disk and File System Management

  • df – Displays information about disk space availability:
  • du – Shows the size of files and directories:
  • mount – Mounts a file system:
  • umount – Unmounts a file system:

8. Searching for Files

  • find – Searches for files in the system:
  • locate – Quickly searches for files in the system:
  • grep – Searches for patterns in files:
  • which – Finds the full path to an executable file:

9. Communicating with the System

  • echo – Displays text on the screen:
  • cat – Displays the contents of a file:
  • more – Displays the contents of a file page by page:
  • less – Similar to more, but offers more navigation options:
  • man – Displays the user manual for a command:

10. Working with Archives

  • tar – Creates or extracts archives:
  • zip – Creates a ZIP archive:
  • unzip – Extracts ZIP files:
  • tar -xvzf – Extracts a TAR.GZ archive:
  • gzip – Compresses files in .gz format:
  • gunzip – Extracts .gz files:

11. System Monitoring

  • uptime – Displays the system uptime and load:
  • dmesg – Displays system messages related to boot and hardware:
  • iostat – Shows input/output system statistics:
  • free – Displays information about RAM:
  • netstat – Displays information about network connections:
  • ss – A modern version of netstat, used for monitoring network connections:

12. Working with System Logs

  • journalctl – Reviews system logs:
  • tail – Displays the last lines of a file:
  • logrotate – Automatically manages logs:

13. Advanced File Operations

  • ln – Creates a link to a file:
  • xargs – Passes arguments from input to other commands:
  • chmod – Changes permissions for files/directories:
  • chattr – Changes file attributes:

Linux offers a wide array of commands that allow for complete control over the computer. Key commands such as ls, cd, cp, and rm are used daily to navigate through the file system, manage files, and directories. To effectively master these commands, it’s best to start with those that are most useful in everyday work. For instance, commands for navigating directories and managing files are fundamental and require practice to become intuitive. Other commands, such as ps for monitoring processes, ping for testing network connections, or chmod for changing permissions, are also worth knowing to fully leverage the power of the Linux system.

To learn effectively, it’s advisable to start by experimenting with commands in practice. Creating files, directories, copying, and deleting data allows for familiarity with their operation. Over time, it’s worthwhile to start combining different commands to solve more advanced problems, such as monitoring processes, managing users, or working with system logs. One can also use documentation, such as man or websites, to delve into the details of each command and its options.

Remember, regular use of the terminal allows for learning habits that make handling the Linux system more natural. Frequent use of commands, solving problems, and experimenting with new commands is the best way to master the system and fully utilize it.

Linux is indeed a powerful tool that provides great control over the system… but remember, don’t experiment on production! After all, experimenting on a production server is a bit like playing Russian roulette — only with bigger consequences. If you want to feel like a true Linux wizard, always test your commands in a development environment. Only then will you be able to learn from mistakes instead of searching for the cause of several gigabytes of data disappearance. And if you don’t know what you’re doing, simply summon your trusty weapon: man!

Enhancing Virtual Machine Management with QEMU Guest Agent on Proxmox


Ever wondered how to streamline the management and monitoring of virtual machines in your Proxmox environment? QEMU Guest Agent is a game-changer, offering tools that significantly enhance the way you interact with virtual systems. Let’s dive into how this tool can transform your setup.

What Makes QEMU Guest Agent Indispensable?

  • Time Synchronization: Keeping time consistent across your virtual machines and the host can be tricky, but QEMU Guest Agent automates this, ensuring that time-sensitive operations run smoothly.
  • Power Management: Imagine being able to shut down or reboot your virtual machines right from the Proxmox panel — no need to log in to each VM. It’s not only convenient but also a time saver.
  • System Monitoring: Get detailed insights into file systems, network activities, and other operational parameters directly from your host. This level of monitoring allows for timely diagnostics and adjustments.
  • Disk Management: Handling disk operations without having to intervene directly on the VM makes backing up and restoring data more straightforward than ever.

Setting Up QEMU Guest Agent on Your Proxmox Server

Getting started with QEMU Guest Agent involves a few simple steps:

  • Enable the Agent: Log in to your Proxmox panel, go to the ‘Options’ section of your desired VM, and make sure the ‘QEMU Guest Agent’ option is checked.

Next up, installing it on an Ubuntu VM:

To check whether the qeumu-guest-agent that can make the change is working properly:

The QEMU Guest Agent doesn’t just make life easier by automating the mundane tasks — it also enhances the security and efficiency of your virtual environment. Whether you’re managing a single VM or a whole fleet, it’s an invaluable addition to your toolkit.

Automatic deletion of files on QNAP drive via SSHFS


Automation of Disk Space Management in a Linux Environment

In today’s digital world, where data is being accumulated in ever-increasing amounts, managing disk space has become a key aspect of maintaining operational efficiency in systems. In this article, I will present a script that automates the process of managing space on a remote disk mounted via SSHFS, particularly useful for system administrators who regularly deal with filling storage media.

Prerequisites

Before starting, ensure that SSHFS and all necessary packages enabling its proper operation are installed on your system. SSHFS allows remote file systems to be mounted via SSH, which is crucial for our script’s operation. To install SSHFS and the necessary tools, including a package that enables password forwarding (sshpass), use the following command:

Bash Script for Disk Space Management

Our Bash script focuses on monitoring and maintaining a defined percentage of free disk space on a remote disk mounted via SSHFS. Here are the script’s main functions:

Goal Definition:

TARGET_USAGE=70 – the percentage of disk space we want to maintain as occupied. The script will work to keep at least 30% of the disk space free.

Mount Point and Paths:

MOUNT_POINT=”/mnt/qnapskorupki” – the local directory where the remote disk is mounted. TARGET_DIRS=”$MOUNT_POINT/up*.soban.pl” – the directories where the script will look for files to delete if needed.

Function check_qnap: This function checks whether the disk is mounted and whether the mount directory is not empty. If there are issues, the script attempts to unmount and remount the disk using sshfs with a password forwarded through sshpass.

File Deletion: The script monitors disk usage and, if TARGET_USAGE is exceeded, it finds and deletes the oldest files in specified directories until the target level of free space is achieved.

Example Script Execution:

script starts working and gradually deletes files

The script will run until it reaches 70% usage as planned:

Script runs until reaching 70%

Downloading the script and adding it to crontab

Of course, the script should be adjusted to meet your specific needs. However, if you want to download it and add it to crontab, follow these steps:

If you want to automate the file removal process, for example, at the end of the day, add the following entry to crontab:

In this case, the script will run every day at 11:55 PM:

Make sure to use the correct path to the script.

Security and Optimization

The script uses a password directly in the command line, which can pose a security risk. In practical applications, it is recommended to use more advanced authentication methods, such as SSH keys, which are more secure and do not require a plaintext password in the script. However, in the case of QNAP, we used a password when writing this script.

Conclusion

The presented script is an example of how daily administrative tasks, such as disk space management, can be automated, thus increasing efficiency and reliability. Its implementation in real IT environments can significantly streamline data management processes, especially in situations where quick response to changes in disk usage is critical.

How to automatically turn off your laptop when battery status is displayed in Linux


Automatically Shutting Down Your Laptop at Low Battery Levels

Maintaining long battery life and protecting data are crucial for laptop users. In this article, we’ll show you how to create a simple Bash script that automatically shuts down your laptop when the battery level falls below 20%. Additionally, you’ll learn how to set up a crontab to run the script every 10 minutes, ensuring continuous monitoring.

Creating a Bash Script

The Bash script we have prepared will check the current battery level and compare it to a set minimum threshold. If the battery level drops below this threshold, the script initiates a system shutdown, helping to protect your data and hardware.

Also you can download script:

Don’t forget to grant permissions to run it:

Crontab Configuration

Crontab is a tool that allows you to schedule tasks in the Linux system. With it, we can set up regular battery checks.

Summary

With this setup, you can rest assured about the condition of your laptop even during intensive use. Automatic shutdown at low battery levels not only protects the equipment but also helps maintain a longer battery life.

Expanding Storage Space in Linux: Step-by-Step Guide using LVM and fdisk

Expanding disk space in Linux virtual machines is a key aspect of server system management. In this article, we show how to effectively increase disk space using LVM and fdisk tools, based on real system data.

Preliminary Preparations

Before making changes to partitions and volumes, it is important to check the current state of the disks in the system. We will use the lsblk command to identify available disks and partitions.

Here is an example of the lsblk command output on a machine:

Creating Snapshots

Before making changes to disk configurations, it is advisable to create a snapshot of the LVM volumes to ensure data can be restored in case of unexpected issues.

Modifying Partitions

Next, we proceed to modify the partitions using fdisk. We remove the existing partition and then create a new one that utilizes the entire available space on disk sdb.

Saving Changes

After properly configuring the partitions, we use the w command in fdisk to save the changes and update the partition table.

Executing pvscan

After modifying the partitions, we execute the pvscan command so the system can update information about available physical volumes.

Configuring LVM

After saving changes to the partition table, we need to update the LVM configuration to include the new disk space. We use the lvextend command with automatic file system resizing.

Summary

Expanding disk space on a Linux virtual machine enhances performance and the availability of storage space. Thanks to the steps described, managing disk space in systems using LVM becomes simpler and more efficient.

Troubleshooting Proxmox clusters and restoring the LXC container

Managing Proxmox clusters can sometimes present technical difficulties, such as inconsistencies in cluster configuration or issues with restoring LXC containers. Finding and resolving these issues is crucial for maintaining the stability and performance of the virtualization environment. In this article, I present a detailed guide on how to diagnose and resolve an issue with an unreachable node and how to successfully restore an LXC container.

Before you begin any actions, make sure you have a current backup of the system.

Diagnosing the State of the Proxmox Cluster

and:

To understand the state of the cluster, execute the following command on the node-up-page-04 node:

Expected output:

Then check the detailed cluster information with the following command:

Expected output:

Removing the Container Configuration File and Cleaning Data

I discovered that the configuration file for container 107 still exists on the cluster’s file system at the path:

Output:

To remove this file and any remaining data associated with the detached node, execute:

Restoring the Container

After removing the configuration file, I restored the LXC container on the node-up-page-04 node using the command:

Output:

The restoration process was successful, and the container was ready for use. This case illustrates the importance of thorough diagnostics and configuration file management in Proxmox when working with clusters. Regular reviews of configurations are advisable to avoid inconsistencies and operational issues in the future.

Resolving performance_schema Issues in MySQL


During daily work with MySQL databases, specific challenges such as missing tables or errors related to the unrecognized database performance_schema can arise. These problems can significantly affect the performance and stability of database systems, and their diagnosis and resolution can often be complicated and time-consuming. To facilitate this task, I have created this guide, which is the result of my experiences and proven practices. I provide a comprehensive approach to identifying and fixing issues related to performance_schema. It’s quite simple to import the schema from a newly built database.

Of course, it’s best to perform a backup of the database before the entire operation.

Initial Diagnosis in MySQL

Start by identifying the problem in the MySQL shell:

Creating New Performance Schema in MySQL

Create a new performance schema from the MySQL command line:

Server Operations to Establish New MySQL Environment

Return to the system to configure a clean MySQL environment:

Then, start MySQL in safe mode to configure it – without external network interruptions:

Configuration and Verification in MySQL

Return to the MySQL command line to verify the configuration and configure the new database:

As you can see, here performance_schema is working correctly.
Update the root password in the MySQL environment to secure the new installation:

Restart MySQL in safe mode to ensure all configurations are applied:

Configure MySQL Server to Run New Database

After securing the new MySQL configuration, update the server configuration to use the new data directory:

Restart the MySQL service to load the my.cnf file during mysql startup:

Export and Restore Performance Schema in MySQL

With the new configuration, export performance_schema using MySQL commands and prepare for its restoration:

It’s necessary to shut down MySQL:

Restore the original MySQL data directory on the server, restart the MySQL service, and import the exported schema:

Make sure the default storage engine is running, e.g:

Don’t forget to remove the trash:

If you’ve reached this point, remember to delete the database backup – as long as everything is working. You did make one, right? 🙂

Setting Up Kerberos and CIFS Resource Mounting on Linux Systems

Ensure the following packages are installed to handle Kerberos authentication and mounting CIFS filesystems:

Kerberos Ticket Initialization

Initialize the Kerberos ticket with the following command:

To verify the ticket’s validity and see details, use:

Manual Resource Mounting

To manually mount a CIFS resource, use the command below. Replace yourserver/yourresource and /your/mountpoint with the appropriate server address and local mount point:

Auto-mounting via fstab

For persistent configuration that survives reboots, add the following entry to your /etc/fstab:

Summary

These settings are crucial for ensuring secure and reliable access to network resources using Kerberos on Linux systems. Always ensure your Kerberos tickets are valid and renew them as necessary. For any issues related to mounting or authentication, refer to the system logs or consult your system administrator.

How to prevent hibernation and sleep on debian and proxmox laptops when the lid is closed

Virtualization servers based on Debian family systems, such as Proxmox, are often used in test environments where continuous availability is crucial. Sometimes these servers are installed on laptops, which serve as low-budget or portable solutions. However, the standard power management settings in laptops can lead to undesirable behaviors, such as sleeping or hibernating when the lid is closed. Below, I describe how to change these settings in an operating system based on Debian to ensure uninterrupted server operation.

Step 1: Accessing the Configuration File

Open the terminal and enter the following command to edit the /etc/systemd/logind.conf file using a text editor (e.g., nano):

Step 2: Modifying logind Settings

Find the line containing HandleLidSwitch and change its value to ignore. If the line is commented out (preceded by a # symbol), remove the #. You can also add this line to the end of the file if it does not exist.

Step 3: Applying and Restarting the Service

After making the changes and saving the file, you need to restart the systemd-logind service for the changes to take effect. Use the following command in the terminal:

With these changes, closing the laptop lid will no longer initiate hibernation or sleep, which is especially important when using Debian-based servers, including Proxmox, as server solutions.

Extending SWAP space on Proxmox using lvreduce

Introduction

Managing SWAP memory is a key element in administering Linux operating systems, especially in virtualization environments like Proxmox. SWAP acts as “virtual memory” that can be used when the system’s physical RAM is full. In this article, we will show how to increase SWAP space on a Proxmox server, using the lvresize tool to free up disk space that can then be allocated to SWAP.

Problem Overview

A user wants to increase SWAP space from 8 GB to 16 GB, but encounters the problem of lacking available space in the LVM volume group, which is required to increase SWAP.

Step 1: Checking Available Space

The command vgs displays the volume groups along with their sizes and available space.

Step 2: Reducing the Volume

Suppose there is a root volume of 457.26 GB, which can be reduced to free up an additional 8 GB for SWAP. Before reducing the volume, it is necessary to reduce the file system on this volume.

However, in the case of the XFS file system, reduction must occur offline or from a live CD.

Step 3: Using lvreduce

This command reduces the root volume by 8 GB, which is confirmed by a message about the volume size change.

Step 4: Deactivating SWAP

Before starting changes in SWAP size, SWAP must first be turned off using the above command.

Step 5: Expanding SWAP

The above commands first increase the SWAP space, then format it and reactivate it.

Finally, we verify the active SWAP areas using the above command to ensure everything is configured correctly.

This process shows how you can flexibly manage disk space on Proxmox servers, adjusting the size of SWAP depending on needs. Using lvreduce requires caution, as any operation on partitions and volumes carries the risk of data loss, therefore it is always recommended to make backups before proceeding with changes.