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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.

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

Posted on January 24, 2025January 24, 2025 by soban

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.

#!/bin/bash

# Define the minimum battery level before shutdown
MIN_BATTERY_LEVEL=20

# Get the current battery level
current_level=$(cat /sys/class/power_supply/BAT0/capacity)

# Check if the current battery level is less than or equal to the minimum level
if [[ "$current_level" -le "$MIN_BATTERY_LEVEL" ]]; then
  echo "Battery level is $current_level%, which is below the threshold of $MIN_BATTERY_LEVEL%. Shutting down..."
  # Shutdown command
  /sbin/shutdown -h now
else
  echo "Battery level is $current_level%, no need to shut down."
fi

#!/bin/bash

# Define the minimum battery level before shutdown

MIN_BATTERY_LEVEL=20

# Get the current battery level

current_level=$(cat /sys/class/power_supply/BAT0/capacity)

# Check if the current battery level is less than or equal to the minimum level

if [[ "$current_level" -le "$MIN_BATTERY_LEVEL" ]]; then

echo "Battery level is $current_level%, which is below the threshold of $MIN_BATTERY_LEVEL%. Shutting down..."

# Shutdown command

/sbin/shutdown -h now

else

echo "Battery level is $current_level%, no need to shut down."

Also you can download script:

wget https://soban.pl/bash/check_battery.sh

1	wget https://soban.pl/bash/check_battery.sh

Don’t forget to grant permissions to run it:

chmod +x check_battery.sh

1	chmod +x check_battery.sh

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.

crontab -e

# Add the following line to crontab to run the script every 10 minutes
*/10 * * * * /root/check_battery.sh > /dev/null 2>&1

crontab -e

# Add the following line to crontab to run the script every 10 minutes

*/10 * * * * /root/check_battery.sh > /dev/null 2>&1

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

Posted on November 13, 2024November 13, 2024 by soban

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.

lsblk

lsblk

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

NAME                      MAJ:MIN RM  SIZE RO TYPE MOUNTPOINT
loop0                       7:0    0 55.7M  1 loop /snap/core18/2829
sda                         8:0    0   42G  0 disk
├─sda1                      8:1    0  512M  0 part /boot/efi
├─sda2                      8:2    0    1G  0 part /boot
└─sda3                      8:3    0 40.5G  0 part
  └─ubuntu--vg-ubuntu--lv 253:0    0 78.5G  0 lvm  /
sdb                         8:16   0  350G  0 disk
└─sdb1                      8:17   0   60G  0 part
  └─ubuntu--vg-ubuntu--lv 253:0    0 78.5G  0 lvm  /
sr0                        11:0    1 1024M  0 rom

NAME MAJ:MIN RM SIZE RO TYPE MOUNTPOINT

loop0 7:0 0 55.7M 1 loop /snap/core18/2829

sda 8:0 0 42G 0 disk

├─sda1 8:1 0 512M 0 part /boot/efi

├─sda2 8:2 0 1G 0 part /boot

└─sda3 8:3 0 40.5G 0 part

└─ubuntu--vg-ubuntu--lv 253:0 0 78.5G 0 lvm /

sdb 8:16 0 350G 0 disk

└─sdb1 8:17 0 60G 0 part

└─ubuntu--vg-ubuntu--lv 253:0 0 78.5G 0 lvm /

sr0 11:0 1 1024M 0 rom

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.

lvcreate -L 20G -s -n my_snapshot /dev/ubuntu-vg/ubuntu-lv

1	lvcreate -L 20G -s -n my_snapshot /dev/ubuntu-vg/ubuntu-lv

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.

fdisk /dev/sdb

1	fdisk /dev/sdb

Saving Changes

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

Command (m for help): w

1	Command (m for help): w

Executing pvscan

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

pvscan

pvscan

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.

lvextend -l +100%FREE /dev/ubuntu-vg/ubuntu-lv -r

1	lvextend -l +100%FREE /dev/ubuntu-vg/ubuntu-lv -r

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

Posted on November 13, 2024November 13, 2024 by soban

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

pvecm delnode up-page-02
Node/IP: up-page-02 is not a known host of the cluster.

1 2	pvecm delnode up-page-02 Node/IP: up-page-02 is not a known host of the cluster.

and:

pct restore 107 vzdump-lxc-107-2024_11_12-03_00_01.tar.zst --storage local
CT 107 already exists on node 'up-page-02'

1 2	pct restore 107 vzdump-lxc-107-2024_11_12-03_00_01.tar.zst --storage local CT 107 already exists on node 'up-page-02'

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

pvecm nodes

1	pvecm nodes

Expected output:

Membership information
----------------------
    Nodeid      Votes Name
         1          1 node-up-page-01
         2          1 node-up-page-04 (local)

Membership information

----------------------

Nodeid Votes Name

1 1 node-up-page-01

2 1 node-up-page-04 (local)

Then check the detailed cluster information with the following command:

pvecm status

1	pvecm status

Expected output:

Cluster information
-------------------
Name:             soban-proxmox
Config Version:   4
Transport:        knet
Secure auth:      on

Quorum information
------------------
Date:             Wed Nov 13 10:40:12 2024
Quorum provider:  corosync_votequorum
Nodes:            2
Node ID:          0x00000002
Ring ID:          1.e6
Quorate:          Yes

Votequorum information
----------------------
Expected votes:   2
Highest expected: 2
Total votes:      2
Quorum:           2
Flags:            Quorate

Membership information
----------------------
    Nodeid      Votes Name
0x00000001          1 <masked IP>
0x00000002          1 <masked IP> (local)

Cluster information

-------------------

Name: soban-proxmox

Config Version: 4

Transport: knet

Secure auth: on

Quorum information

------------------

Date: Wed Nov 13 10:40:12 2024

Quorum provider: corosync_votequorum

Nodes: 2

Node ID: 0x00000002

Ring ID: 1.e6

Quorate: Yes

Votequorum information

----------------------

Expected votes: 2

Highest expected: 2

Total votes: 2

Quorum: 2

Flags: Quorate

Membership information

----------------------

Nodeid Votes Name

0x00000001 1 <masked IP>

0x00000002 1 <masked IP> (local)

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:

ls -ltr /etc/pve/nodes/node-up-page-02/lxc/107.conf

1	ls -ltr /etc/pve/nodes/node-up-page-02/lxc/107.conf

Output:

-rw-r----- 1 root www-data 235 Nov 12 21:35 /etc/pve/nodes/node-up-page-02/lxc/107.conf

1	-rw-r----- 1 root www-data 235 Nov 12 21:35 /etc/pve/nodes/node-up-page-02/lxc/107.conf

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

rm -rf /etc/pve/nodes/node-up-page-02/

1	rm -rf /etc/pve/nodes/node-up-page-02/

Restoring the Container

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

pct restore 107 /root/vzdump-lxc-107-2024_11_12-03_00_01.tar.zst --storage local

1	pct restore 107 /root/vzdump-lxc-107-2024_11_12-03_00_01.tar.zst --storage local

Output:

recovering backed-up configuration from '/root/vzdump-lxc-107-2024_11_12-03_00_01.tar.zst'
Formatting '/var/lib/vz/images/107/vm-107-disk-0.raw', fmt=raw size=59055800320 preallocation=off
Creating filesystem with 14417920 4k blocks and 3604480 inodes
Filesystem UUID: 8b707e55-5e14-4b20-8585-6cb09e0fa520
Superblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 4096000, 7962624, 11239424
restoring '/root/vzdump-lxc-107-2024_11_12-03_00_01.tar.zst' now..
extracting archive '/root/vzdump-lxc-107-2024_11_12-03_00_01.tar.zst'

recovering backed-up configuration from '/root/vzdump-lxc-107-2024_11_12-03_00_01.tar.zst'

Formatting '/var/lib/vz/images/107/vm-107-disk-0.raw', fmt=raw size=59055800320 preallocation=off

Creating filesystem with 14417920 4k blocks and 3604480 inodes

Filesystem UUID: 8b707e55-5e14-4b20-8585-6cb09e0fa520

Superblock backups stored on blocks: 32768, 98304, 163840, 229376, 294912, 819200, 884736, 1605632, 2654208, 4096000, 7962624, 11239424

restoring '/root/vzdump-lxc-107-2024_11_12-03_00_01.tar.zst' now..

extracting archive '/root/vzdump-lxc-107-2024_11_12-03_00_01.tar.zst'

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

Posted on November 7, 2024November 7, 2024 by soban

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:

SHOW VARIABLES LIKE 'default_storage_engine';
ERROR 1146 (42S02): Table 'performance_schema.session_variables' doesn't exist
USE performance_schema;
ERROR 1049 (42000): Unknown database 'performance_schema';

SHOW VARIABLES LIKE 'default_storage_engine';

ERROR 1146 (42S02): Table 'performance_schema.session_variables' doesn't exist

USE performance_schema;

ERROR 1049 (42000): Unknown database 'performance_schema';

Creating New Performance Schema in MySQL

Create a new performance schema from the MySQL command line:

CREATE DATABASE performance_schema;
shutdown;
\q

CREATE DATABASE performance_schema;

shutdown;

Server Operations to Establish New MySQL Environment

Return to the system to configure a clean MySQL environment:

systemctl stop mysql.service
mkdir /var/lib/mysql_new
mysqld --initialize --user=mysql --basedir=/usr --datadir=/var/lib/mysql_new
chown -R mysql:mysql /var/lib/mysql_new
cd /var/lib/mysql_new

systemctl stop mysql.service

mkdir /var/lib/mysql_new

mysqld --initialize --user=mysql --basedir=/usr --datadir=/var/lib/mysql_new

chown -R mysql:mysql /var/lib/mysql_new

cd /var/lib/mysql_new

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

sudo -u mysql mysqld_safe --datadir=/var/lib/mysql_new --skip-grant-tables --skip-networking

1	sudo -u mysql mysqld_safe --datadir=/var/lib/mysql_new --skip-grant-tables --skip-networking

Configuration and Verification in MySQL

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

mysql -u root
SHOW DATABASES;
USE performance_schema;
SHOW TABLES;

mysql -u root

SHOW DATABASES;

USE performance_schema;

SHOW TABLES;

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

USE mysql;
UPDATE user SET authentication_string=PASSWORD('NewSecurePassword');
FLUSH PRIVILEGES;
shutdown;
\q

USE mysql;

UPDATE user SET authentication_string=PASSWORD('NewSecurePassword');

FLUSH PRIVILEGES;

shutdown;

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

sudo -u mysql mysqld_safe --datadir=/var/lib/mysql_new --skip-networking

1	sudo -u mysql mysqld_safe --datadir=/var/lib/mysql_new --skip-networking

Configure MySQL Server to Run New Database

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

vi /etc/mysql/my.cnf
# Change datadir to:
datadir=/var/lib/mysql_new

vi /etc/mysql/my.cnf

# Change datadir to:

datadir=/var/lib/mysql_new

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

systemctl start mysql.service

1	systemctl start mysql.service

Export and Restore Performance Schema in MySQL

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

mysqldump -u root -p --no-data --skip-lock-tables performance_schema > /root/performance_schema.sql

1	mysqldump -u root -p --no-data --skip-lock-tables performance_schema > /root/performance_schema.sql

It’s necessary to shut down MySQL:

shutdown;
\q

1 2	shutdown; \q

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

vi /etc/mysql/my.cnf
# Change datadir back to:
datadir=/var/lib/mysql_old
systemctl start mysql.service
mysql -u root -p performance_schema < /root/performance_schema.sql
systemctl restart mysql.service

vi /etc/mysql/my.cnf

# Change datadir back to:

datadir=/var/lib/mysql_old

systemctl start mysql.service

mysql -u root -p performance_schema < /root/performance_schema.sql

systemctl restart mysql.service

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

SHOW VARIABLES LIKE 'default_storage_engine';
+------------------------+--------+
| Variable_name          | Value  |
+------------------------+--------+
| default_storage_engine | InnoDB |
+------------------------+--------+
1 row in set (0.00 sec)

SHOW VARIABLES LIKE 'default_storage_engine';

+------------------------+--------+

| Variable_name | Value |

+------------------------+--------+

| default_storage_engine | InnoDB |

+------------------------+--------+

1 row in set (0.00 sec)

Don’t forget to remove the trash:

rm -rf /var/lib/mysql_new/ /root/performance_schema.sql

1	rm -rf /var/lib/mysql_new/ /root/performance_schema.sql

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

Posted on May 31, 2024June 5, 2024 by soban

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

apt install krb5-user cifs-utils keyutils

1	apt install krb5-user cifs-utils keyutils

Kerberos Ticket Initialization

Initialize the Kerberos ticket with the following command:

kinit yourname@yourdomain.com

1	kinit yourname@yourdomain.com

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

klist

klist

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:

mount -t cifs //yourserver/yourshare /yourmountpoint -o sec=krb5,cruid=0,uid=0,gid=0,vers=3.1.1,noperm,dir_mode=0777,file_mode=0777,iocharset=utf8

1	mount -t cifs //yourserver/yourshare /yourmountpoint -o sec=krb5,cruid=0,uid=0,gid=0,vers=3.1.1,noperm,dir_mode=0777,file_mode=0777,iocharset=utf8

Auto-mounting via fstab

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

//yourserver/yourshare /yourmountpoint cifs sec=krb5,cruid=0,uid=0,gid=0,vers=3.1.1,noperm,dir_mode=0777,file_mode=0777,iocharset=utf8,_netdev,x-systemd.automount,x-systemd.requires=network-online.target 0 0

1	//yourserver/yourshare /yourmountpoint cifs sec=krb5,cruid=0,uid=0,gid=0,vers=3.1.1,noperm,dir_mode=0777,file_mode=0777,iocharset=utf8,_netdev,x-systemd.automount,x-systemd.requires=network-online.target 0 0

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

Posted on April 19, 2024April 19, 2024 by soban

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):

nano /etc/systemd/logind.conf

1	nano /etc/systemd/logind.conf

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.

HandleLidSwitch=ignore

1	HandleLidSwitch=ignore

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:

systemctl restart systemd-logind

1	systemctl restart systemd-logind

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

Posted on April 18, 2024 by soban

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

vgs

vgs

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.

resize2fs /dev/pve/root 449.26G

1	resize2fs /dev/pve/root 449.26G

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

Step 3: Using lvreduce

lvreduce -L -8G /dev/pve/root

1	lvreduce -L -8G /dev/pve/root

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

Step 4: Deactivating SWAP

swapoff -a

1	swapoff -a

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

Step 5: Expanding SWAP

lvresize -L +8G /dev/pve/swap
mkswap /dev/pve/swap
swapon /dev/pve/swap

lvresize -L +8G /dev/pve/swap

mkswap /dev/pve/swap

swapon /dev/pve/swap

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

swapon --show

1	swapon --show

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.