Linux KVM hypervisor a beginners guide

 Linux KVM. KVM is a virtualization technology for Linux that allows you to create and run virtual machines (VMs) on a Linux host.

Before we begin, make sure that you have a Linux machine with KVM installed. You can install KVM on Ubuntu or Debian with the following command:

sudo apt-get install qemu-kvm libvirt-bin bridge-utils virt-manager

For Red Hat-based systems, you can use the following command:

sudo yum install qemu-kvm libvirt bridge-utils virt-manager

Once you have KVM installed, you can start creating VMs.

Creating a Virtual Machine

You can create a VM using the virt-install command. Here is an example command:

sudo virt-install \

--name my-vm \

--ram 2048 \

--vcpus 2 \

--disk path=/var/lib/libvirt/images/my-vm.qcow2,size=10 \

--os-type linux \

--os-variant ubuntu20.04 \

--network bridge=virbr0 \

--graphics none \

--console pty,target_type=serial \

--location 'http://archive.ubuntu.com/ubuntu/dists/focal/main/installer-amd64/'

This command creates a VM named my-vm with 2 vCPUs and 2GB of RAM. The VM has a 10GB disk and uses the Ubuntu 20.04 operating system. The VM is connected to a virtual bridge named virbr0 and has no graphics output. The console output is redirected to a serial port. Finally, the VM is installed from an Ubuntu 20.04 installation ISO available at the given URL.

You can adjust the parameters of this command to suit your needs. For example, you can change the name of the VM, the amount of RAM and vCPUs, the disk size and location, and the network settings.

Starting and Stopping a Virtual Machine

To start a VM, use the virsh start command followed by the name of the VM:

sudo virsh start my-vm

To stop a VM, use the virsh shutdown command followed by the name of the VM:

sudo virsh shutdown my-vm

Listing Virtual Machines

To list all the VMs on your system, use the virsh list command:

sudo virsh list --all

This command lists all the running and stopped VMs on your system.

Managing Virtual Machines with Virt-Manager

Virt-Manager is a graphical user interface for managing virtual machines. To start Virt-Manager, type the following command in a terminal:

virt-manager

This command opens the Virt-Manager window, where you can view and manage your VMs.

To create a new VM using Virt-Manager, click the Create a new virtual machine button in the toolbar. This opens a wizard that guides you through the process of creating a new VM.

Conclusion

In this tutorial, we have covered the basics of creating, starting, and stopping virtual machines using KVM on Linux. We have also covered some of the CLI commands and configuration examples for managing virtual machines. With this knowledge, you can start using KVM to create and manage virtual machines on your Linux host.

How to remove (^M) characters from a file in Linux

The control characters "^M" in a text file are actually the line endings used by Windows/DOS operating systems. These characters can cause issues when you try to use the file in Linux. Fortunately, it is easy to remove them using the tr command

tr -d '\r' < original_file.txt > new_file.txt

That's it! This is a quick and simple way to remove the control characters "^M" from a text file in Linux.

Using the find -exec Command Option

 The -exec option allows you to execute a command on each file or directory that matches the search criteria specified with the find command.

Here are some examples of using the -exec option with the find command:

1. Delete all files with a certain extension:

You can use the -exec option with the rm command to delete all files with a certain extension. For example, to delete all files with the extension .log in the current directory and its subdirectories, use the following command:

find . -name "*.log" -type f -exec rm {} \;

2. Change the ownership of files:

You can use the -exec option with the chown command to change the ownership of files. For example, to change the ownership of all files with the extension .txt to the user john in the current directory and its subdirectories, use the following command:

find . -name "*.txt" -type f -exec chown john {} \;

3. Compress all files in a directory:

You can use the -exec option with the gzip command to compress all files in a directory. For example, to compress all files in the current directory and its subdirectories, use the following command:

find . -type f -exec gzip {} \;

4. Copy files to another directory:

You can use the -exec option with the cp command to copy files to another directory. For example, to copy all files with the extension .txt to the directory /home/user/documents, use the following command:

find . -name "*.txt" -type f -exec cp {} /home/user/documents \;

5. Rename files with a certain pattern:

You can use the -exec option with the mv command to rename files with a certain pattern. For example, to rename all files with the extension .txt to have the extension .doc in the current directory and its subdirectories, use the following command:

find . -name "*.txt" -type f -exec mv {} {}.doc \;

These are just a few examples of the many ways you can use the -exec option with the find command to execute commands on files or directories that match your search criteria.

Practical examples of Linux Find command

The find command in Linux is a powerful utility used to search for files and directories in a given directory hierarchy. It is a command-line tool that offers many options to filter and refine the search results.

Here's a step-by-step guide on how to use the find command with examples for various switches:

1. Basic usage

The basic usage of the find command is as follows:

find /path/to/search -name "filename"

This command searches for files with the given name in the specified path.

Example: To find all files named example.txt in the current directory and its subdirectories, use the following command:

find . -name "example.txt"

2. Search by file type

You can use the -type option to search for files of a specific type.

Example: To find all directories in the current directory and its subdirectories, use the following command:

find . -type d

To find all files in the current directory and its subdirectories, use the following command:

find . -type f

3. Search by file size

You can use the -size option to search for files of a specific size. The size can be specified in bytes, kilobytes, megabytes, or gigabytes.

Example: To find all files in the current directory and its subdirectories that are larger than 1 MB, use the following command:

find . -size +1M

4. Search by modification time

You can use the -mtime option to search for files based on their modification time. The time can be specified in days.

Example: To find all files in the current directory and its subdirectories that have been modified within the last 7 days, use the following command:

find . -mtime -7

5. Search by user or group

You can use the -user and -group options to search for files owned by a specific user or group.

Example: To find all files in the current directory and its subdirectories that are owned by the user john, use the following command:

find . -user john

To find all files in the current directory and its subdirectories that are owned by the group developers, use the following command:

find . -group developers

6. Search by permissions:

You can use the -perm option to search for files based on their permissions.

Example: To find all files in the current directory and its subdirectories that have read and write permissions for the owner and read permissions for others, use the following command:

find . -perm 644

7. Search by name with wildcard:

You can use the * and ? characters as wildcards to search for files with a pattern in their name.

Example: To find all files in the current directory and its subdirectories that have the word example in their name, use the following command:

find . -name "*example*"

8. Search by exclusion:

You can use the ! character to exclude files or directories from the search results.

Example: To find all files in the current directory and its subdirectories that are not named example.txt, use the following command:

find . ! -name "example.txt"

These are just a few examples of the many options available with the find command in Linux. By combining these options, you can perform complex searches to locate the files or directories you need.

Understanding the Linux dd Command

The dd command stands for "data duplicator" and is used for copying and converting data. The command operates at the block level, meaning that it copies data block by block, rather than file by file. This allows you to copy or manipulate data at a low level, which can be useful in certain situations.

Syntax

The basic syntax of the dd command is as follows:

dd if=input-file of=output-file [options]

Here, "if" stands for "input file," and "of" stands for "output file." You can specify any file as the input or output file, including disks and partitions.

Common Uses

1. Creating a Bootable USB Drive

One of the most common uses of the dd command is to create a bootable USB drive. To do this, you'll need an ISO file of the operating system you want to install, as well as a USB drive with enough space to hold the ISO file. Here's the command to create a bootable USB drive using dd:

dd if=/path/to/iso_file.iso of=/dev/sdb bs=4M status=progress && sync

Here, /path/to/iso_file.iso is the path to the ISO file you want to copy, and /dev/sdb is the path to the USB drive you want to copy it to. Note that you should replace /dev/sdb with the path to your own USB drive.

2. Cloning a Disk

Another common use of the dd command is to clone a disk. This can be useful if you want to create a backup of a disk or copy the contents of one disk to another. Here's the command to clone a disk using dd:

dd if=/dev/sda of=/dev/sdb bs=4M status=progress && sync

Here, /dev/sda is the path to the disk you want to clone, and /dev/sdb is the path to the destination disk. Again, make sure you replace /dev/sda and /dev/sdb with the paths to your own disks.

3. Erasing a Disk

You can also use the dd command to erase the contents of a disk. This can be useful if you want to securely wipe a disk before selling or disposing of it. Here's the command to erase a disk using dd:

dd if=/dev/zero of=/dev/sda bs=4M status=progress && sync

Here, /dev/zero is a special file in Linux that contains only zeros, and /dev/sda is the path to the disk you want to erase. This command overwrites the entire disk with zeros, effectively erasing all data on the disk.

4. Checking Disk I/O

You can use the dd command to check the input/output (I/O) performance of a disk. To do this, you can create a large file on the disk and then read it back to measure the disk's read speed. Here's the command to do that:

dd if=/dev/zero of=testfile bs=1M count=1000 conv=fdatasync

This command creates a 1GB file called "testfile" filled with zeros on the disk. The conv=fdatasync option ensures that the data is written to disk immediately. You can then read the file back to measure the disk's read speed:

dd if=testfile of=/dev/null bs=1M count=1000

This command reads the "testfile" from the disk and discards the output by writing it to /dev/null. The bs=1M option sets the block size to 1MB, and the count=1000 option reads 1000 blocks of 1MB each

The output of the second dd command will show you the read speed of the disk. You can use this technique to check the write speed of the disk by reversing the if and of options in the commands.

5. Checking Disk Throughput

You can also use the dd command to measure the throughput of a disk. To do this, you can create a large file on the disk and then measure the time it takes to write or read the file. Here's an example

dd if=/dev/zero of=testfile bs=1M count=1000 conv=fdatasync

This command creates a 1GB file called "testfile" filled with zeros on the disk, just like in the previous example. You can then measure the time it takes to read or write the file using the time command:

time dd if=testfile of=/dev/null bs=1M count=1000

This command reads the "testfile" from the disk and discards the output, just like in the previous example. The time command shows you the elapsed time, user CPU time, and system CPU time taken by the dd command.

You can use this technique to measure the throughput of the disk for both reading and writing operations. By dividing the size of the file by the elapsed time, you can calculate the throughput in bytes per second, kilobytes per second, or megabytes per second

Conclusion

The dd command is a powerful utility in Linux that can be used for various disk-related tasks. In this tutorial, we discussed how the dd command works and some of its most common uses, including creating a bootable USB drive, cloning a disk, and erasing a disk. With this knowledge, you should be able to use the dd command to perform a variety of disk-related tasks in Linux

AWK Linux command for search and replace pattern in a file

 Here are some examples of how to use AWK for searching file contents and replacing text in a file

Searching file contents:

To search for a specific pattern in a file, you can use the following command:

awk '/pattern/' filename

For example, to search for the word "example" in a file called "file.txt", you would use the following command:

awk '/example/' file.txt

To search for a pattern and print the lines that match, you can use the following command:

awk '/pattern/ { print }' filename

For example, to search for the word "example" in a file called "file.txt" and print the lines that match, you would use the following command:

awk '/example/ { print }' file.txt

Replacing text in a file:

To replace a specific pattern with a new text in a file, you can use the following command:

awk '{ gsub(/pattern/, "newtext"); print }' filename

For example, to replace the word "example" with the word "test" in a file called "file.txt", you would use the following command:

awk '{ gsub(/example/, "test"); print }' file.txt

To replace a pattern and save the changes back to the original file, you can use the following command:

awk '{ gsub(/pattern/, "newtext"); print > "newfile" }' filename

For example, to replace the word "example" with the word "test" in a file called "file.txt" and save the changes back to the original file, you would use the following command:

awk '{ gsub(/example/, "test"); print > "file.txt" }' file.txt

Linux Distributions overview

 Linux is an open-source operating system that comes in many different distributions, each with its own unique features and benefits. Here is an overview of some of the most popular Linux distributions and what they offer:

1. Ubuntu - Ubuntu is one of the most popular Linux distributions, known for its ease of use and user-friendly interface. It is based on Debian and comes with the GNOME desktop environment. Ubuntu is often used for desktop and laptop computers but can also be used for servers. It offers a wide range of pre-installed software, making it a good choice for beginners.

2. Debian - Debian is one of the oldest Linux distributions, known for its stability and security. It is a popular choice for servers, but can also be used for desktops and laptops. Debian comes with a variety of desktop environments, including GNOME, KDE, Xfce, and LXDE. It offers a large repository of software packages, making it easy to find and install the software you need.

3. Fedora - Fedora is a community-driven distribution sponsored by Red Hat. It is known for its cutting-edge software and frequent releases. Fedora comes with the GNOME desktop environment, but other desktop environments are available. It is often used for development and testing, but can also be used for general desktop and laptop use.

4. CentOS - CentOS is a free, community-driven distribution based on Red Hat Enterprise Linux (RHEL). It is known for its stability and security, making it a popular choice for servers. CentOS comes with a variety of desktop environments, but it is primarily used for server applications.

5. Arch Linux - Arch Linux is a minimalist distribution known for its flexibility and customization options. It comes with a lightweight desktop environment, but users are free to install and customize their own desktop environments. Arch Linux is often used by advanced users who want complete control over their system.

6. Mint - Mint is a popular Linux distribution known for its ease of use and user-friendly interface. It is based on Ubuntu and comes with the Cinnamon desktop environment. Mint is often used for desktop and laptop computers, but can also be used for servers. It offers a variety of pre-installed software, making it a good choice for beginners.

7. OpenSUSE - OpenSUSE is a community-driven distribution sponsored by SUSE Linux GmbH. It is known for its stability and security, making it a popular choice for servers. OpenSUSE comes with the KDE Plasma desktop environment, but other desktop environments are available.

Each of these Linux distributions has its own unique features and benefits, and the choice ultimately depends on your specific needs and preferences. However, all Linux distributions offer the benefits of open-source software, including flexibility, security, and customizability.