February 2025

The most important Linux commands that every user should know

Posted on February 20, 2025February 20, 2025 by soban

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:

pwd

pwd

ls – Lists the contents of a directory. You can use the -l option for a detailed view or -a to show hidden files:

ls -a

ls -a

cd – Changes the directory. For example, cd /home/user will move you to the /home/user directory:

cd ~

cd ~

mkdir – Creates a new directory:

mkdir projects

1	mkdir projects

rmdir – Removes an empty directory:

rmdir old_files

1	rmdir old_files

2. File Management

cp – Copies files or directories:

cp document.txt new_directory/

1	cp document.txt new_directory/

mv – Moves or renames files/directories:

mv file.txt /home/user/new_directory/

1	mv file.txt /home/user/new_directory/

rm – Removes files or directories. Use the -r option to remove a directory with its contents:

rm -r old_data

1	rm -r old_data

touch – Creates an empty file or updates the modification time of an existing file:

touch report.txt

1	touch report.txt

3. Process Management

ps – Displays currently running processes. Use the -aux option to see all processes:

ps -aux

ps -aux

top – Displays a dynamic list of processes in real time:

top

top

kill – Stops a process by its ID:

kill 1234

kill 1234

bg and fg – Manage background and foreground processes:

fg

4. User and Permission Management

sudo – Allows a command to be executed with administrator privileges:

sudo apt update

1	sudo apt update

chmod – Changes permissions for files/directories:

chmod 755 script.sh

1	chmod 755 script.sh

chown – Changes the owner of a file/directory:

chown admin:admin file.txt

1	chown admin:admin file.txt

useradd and userdel – Adds and removes users:

useradd janek

1	useradd janek

5. Networking and Communication

ping – Checks the connection with another host:

ping 192.168.1.1

1	ping 192.168.1.1

ifconfig – Displays information about network interfaces:

ifconfig

ifconfig

ssh – Connects remotely to another computer:

ssh user@192.168.1.2

1	ssh user@192.168.1.2

scp – Copies files over SSH:

scp file.txt user@host:/home/user/

1	scp file.txt user@host:/home/user/

6. Command Usage Examples

Below is an example of using several discussed commands:

chmod – Changes permissions for files/directories:

chmod 755 script.sh

1	chmod 755 script.sh

chown – Changes the owner of a file/directory:

chown admin:developers logs.txt

1	chown admin:developers logs.txt

useradd and userdel – Adds and removes users:

useradd janek

1	useradd janek

7. Disk and File System Management

df – Displays information about disk space availability:

df -h

df -h

du – Shows the size of files and directories:

du -sh documents

1	du -sh documents

mount – Mounts a file system:

mount /dev/sdb1 /mnt/external

1	mount /dev/sdb1 /mnt/external

umount – Unmounts a file system:

umount /mnt/external

1	umount /mnt/external

8. Searching for Files

find – Searches for files in the system:

Find files
Shell

find /home/user -name "*.txt"

1

find /home/user -name "*.txt"
locate – Quickly searches for files in the system:

Locate file
Shell

locate file.txt

1

locate file.txt
grep – Searches for patterns in files:

Search error in syslog
Shell

grep "error" /var/log/syslog

1

grep "error" /var/log/syslog
which – Finds the full path to an executable file:

Check Python location
Shell

which python

1

which python

9. Communicating with the System

echo – Displays text on the screen:

Hello World
Shell

echo "Hello, World!"

1

echo "Hello, World!"
cat – Displays the contents of a file:

Display file content
Shell

cat file.txt

1

cat file.txt
more – Displays the contents of a file page by page:

Display file by pages
Shell

more file.txt

1

more file.txt
less – Similar to more, but offers more navigation options:

Navigate file
Shell

less file.txt

1

less file.txt
man – Displays the user manual for a command:

Manual page for ls
Shell

man ls

1

man ls

10. Working with Archives

tar – Creates or extracts archives:

Creating an archive
Shell

tar -czvf projects.tar.gz projects/

1

tar -czvf projects.tar.gz projects/
zip – Creates a ZIP archive:

Creating a ZIP file
Shell

zip archive.zip file1.txt file2.txt

1

zip archive.zip file1.txt file2.txt
unzip – Extracts ZIP files:

Extracting a ZIP file
Shell

unzip archive.zip

1

unzip archive.zip
tar -xvzf – Extracts a TAR.GZ archive:

Extracting a TAR.GZ archive
Shell

tar -xvzf archive.tar.gz

1

tar -xvzf archive.tar.gz
gzip – Compresses files in .gz format:

Compressing a .gz file
Shell

gzip file.txt

1

gzip file.txt
gunzip – Extracts .gz files:

Extracting a .gz file
Shell

gunzip file.txt.gz

1

gunzip file.txt.gz

11. System Monitoring

uptime – Displays the system uptime and load:

Checking system uptime
Shell

uptime

1

uptime
dmesg – Displays system messages related to boot and hardware:

Checking system errors
Shell

dmesg | grep error

1

dmesg | grep error
iostat – Shows input/output system statistics:

Monitoring I/O statistics
Shell

iostat

1

iostat
free – Displays information about RAM:

Checking RAM
Shell

free -h

1

free -h
netstat – Displays information about network connections:

Monitoring network connections
Shell

netstat -tuln

1

netstat -tuln
ss – A modern version of netstat, used for monitoring network connections:

Monitoring network connections (modern version)
Shell

ss -tuln

1

ss -tuln

12. Working with System Logs

journalctl – Reviews system logs:

Reviewing system logs
Shell

journalctl -u apache2

1

journalctl -u apache2
tail – Displays the last lines of a file:

Tracking system logs
Shell

tail -f /var/log/syslog

1

tail -f /var/log/syslog
logrotate – Automatically manages logs:

Log rotation
Shell

logrotate /etc/logrotate.conf

1

logrotate /etc/logrotate.conf

13. Advanced File Operations

ln – Creates a link to a file:

Creating a symbolic link
Shell

ln -s /path/to/file.txt /path/to/link.txt

1

ln -s /path/to/file.txt /path/to/link.txt
xargs – Passes arguments from input to other commands:

Processing files
Shell

find . -name "*.txt" | xargs cat

1

find . -name "*.txt" | xargs cat
chmod – Changes permissions for files/directories:

Changing permissions
Shell

chmod 755 file.txt

1

chmod 755 file.txt
chattr – Changes file attributes:

Changing file attributes
Shell

chattr +i file.txt

1

chattr +i file.txt

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

Posted on February 11, 2025February 11, 2025 by soban

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:

sudo apt-get install qemu-guest-agent
sudo systemctl start qemu-guest-agent
sudo systemctl enable qemu-guest-agent

sudo apt-get install qemu-guest-agent

sudo systemctl start qemu-guest-agent

sudo systemctl enable qemu-guest-agent

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

systemctl status qemu-guest-agent

1	systemctl status qemu-guest-agent

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

Posted on February 7, 2025February 11, 2025 by soban

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:

apt-get update
apt-get install sshfs fuse sshpass -y

1 2	apt-get update apt-get install sshfs fuse sshpass -y

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.

#!/bin/bash

TARGET_USAGE=70
MOUNT_POINT="/mnt/qnapskorupki"
TARGET_DIRS="$MOUNT_POINT/up*.soban.pl"

# Function to check and mount SSHFS
function check_qnap {
    local remote_path="/share/MD0_DATA/backup_proxmox/"
    local user_remote="remote_user"
    local remote_host="192.168.1.XX"
    local port=22
    local password='XXXXXXXXXXXXXXXXXXXXXXX'

    # Check if the mounting directory exists and is empty
    if [ ! -d "$MOUNT_POINT" ] || [ -z "$(ls -A $MOUNT_POINT)" ]; then
        echo "Problem: The directory $MOUNT_POINT is missing or empty. Attempting to remount..."

        # Unmount if anything is currently mounted
        if mountpoint -q $MOUNT_POINT; then
            echo "Unmounting $MOUNT_POINT..."
            fusermount -u $MOUNT_POINT
            sleep 5
        fi

        # Remount
        echo "Mounting SSHFS: $user_remote@$remote_host:$remote_path to $MOUNT_POINT..."
        echo $password | sshfs $user_remote@$remote_host:$remote_path $MOUNT_POINT -o password_stdin

        # Check if the mounting was successful
        if mountpoint -q $MOUNT_POINT; then
            echo "QNAP successfully mounted."
        else
            echo "Error: Failed to mount $remote_host:$remote_path to $MOUNT_POINT."
            exit 1
        fi
    fi
}

# Check and mount the disk
check_qnap

# Begin deleting files
current_usage=$(df --output=pcent "$MOUNT_POINT" | tail -n 1 | tr -d '%')
echo "Current usage: $current_usage%"
target_free_space=$((100 - $TARGET_USAGE))

# Continue deleting files until the required free space is achieved
while [[ $current_usage -gt $TARGET_USAGE ]]; do
    # Find the oldest file in the target directories
    oldest_file=$(find $TARGET_DIRS -type f -printf '%T+ %p\n' | sort | head -n 1 | cut -d' ' -f2)

    if [ -z "$oldest_file" ]; then
        echo "No files to delete."
        break
    fi

    # Delete the oldest file
    echo "Deleting file $oldest_file..."
    rm -f "$oldest_file"

    # Check usage again
    current_usage=$(df --output=pcent "$MOUNT_POINT" | tail -n 1 | tr -d '%')
    echo "New usage after deletion: $current_usage%"
done

echo "Target disk usage achieved."

#!/bin/bash

TARGET_USAGE=70

MOUNT_POINT="/mnt/qnapskorupki"

TARGET_DIRS="$MOUNT_POINT/up*.soban.pl"

# Function to check and mount SSHFS

function check_qnap {

local remote_path="/share/MD0_DATA/backup_proxmox/"

local user_remote="remote_user"

local remote_host="192.168.1.XX"

local port=22

local password='XXXXXXXXXXXXXXXXXXXXXXX'

# Check if the mounting directory exists and is empty

if [ ! -d "$MOUNT_POINT" ] || [ -z "$(ls -A $MOUNT_POINT)" ]; then

echo "Problem: The directory $MOUNT_POINT is missing or empty. Attempting to remount..."

# Unmount if anything is currently mounted

if mountpoint -q $MOUNT_POINT; then

echo "Unmounting $MOUNT_POINT..."

fusermount -u $MOUNT_POINT

sleep 5

# Remount

echo "Mounting SSHFS: $user_remote@$remote_host:$remote_path to $MOUNT_POINT..."

echo $password | sshfs $user_remote@$remote_host:$remote_path $MOUNT_POINT -o password_stdin

# Check if the mounting was successful

if mountpoint -q $MOUNT_POINT; then

echo "QNAP successfully mounted."

else

echo "Error: Failed to mount $remote_host:$remote_path to $MOUNT_POINT."

exit 1

}

# Check and mount the disk

check_qnap

# Begin deleting files

current_usage=$(df --output=pcent "$MOUNT_POINT" | tail -n 1 | tr -d '%')

echo "Current usage: $current_usage%"

target_free_space=$((100 - $TARGET_USAGE))

# Continue deleting files until the required free space is achieved

while [[ $current_usage -gt $TARGET_USAGE ]]; do

# Find the oldest file in the target directories

oldest_file=$(find $TARGET_DIRS -type f -printf '%T+ %p\n' | sort | head -n 1 | cut -d' ' -f2)

if [ -z "$oldest_file" ]; then

echo "No files to delete."

break

# Delete the oldest file

echo "Deleting file $oldest_file..."

rm -f "$oldest_file"

# Check usage again

current_usage=$(df --output=pcent "$MOUNT_POINT" | tail -n 1 | tr -d '%')

echo "New usage after deletion: $current_usage%"

done

echo "Target disk usage achieved."

Example Script Execution:

script starts working and gradually deletes files

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

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:

wget soban.pl/bash/remove_old_files.sh
chmod +x remove_old_files.sh

1 2	wget soban.pl/bash/remove_old_files.sh chmod +x remove_old_files.sh

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

crontab -e

1	crontab -e

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

45 23 * * * /root/scripts/remove_old_files.sh > /dev/null 2>&1

1	45 23 * * * /root/scripts/remove_old_files.sh > /dev/null 2>&1

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.