Monthly Archives: February 2024

How to fix “network ‘default’ is not active” error in libvirt

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root@debian01:~# virsh net-list –all

Name State Autostart Persistent

default inactive no yes

root@debian01:~# virsh net-start default
Network default started

root@debian01:~# virsh net-autostart default
Network default marked as autostarted

root@debian01:~# virsh net-list –all

Name State Autostart Persistent

default active yes yes

root@debian01:~#

Xen open-source hypervisor command line reference

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Xen is a popular open-source hypervisor that allows for running multiple virtual machines on a single physical host. Here are some common command-line references for managing Xen:

  1. Starting and Stopping Xen:
    • xl create <config_file>: Start a virtual machine defined in the specified configuration file.
    • xl destroy <domain_name>: Forcefully shutdown a virtual machine.
    • xl shutdown <domain_name>: Gracefully shutdown a virtual machine.
    • xl list: List all running domains.
    • xl console <domain_name>: Connect to the console of a running virtual machine.
  2. Managing Virtual Machine Configurations:
    • xl list: List all virtual machines and their states.
    • xl info: Display information about the Xen hypervisor.
    • xl config-list: List all defined VM configurations.
    • xl config-edit <domain_name>: Edit the configuration file of a virtual machine.
    • xl save <domain_name> <state_file>: Save the state of a virtual machine to a file.
    • xl restore <state_file>: Restore a virtual machine from a saved state.
  3. Resource Management:
    • xl mem-set <domain_name> <memory_in_mb>: Set the memory allocation for a virtual machine.
    • xl vcpu-set <domain_name> <num_vcpus>: Set the number of virtual CPUs for a virtual machine.
  4. Networking:
    • Xen usually relies on Linux networking configuration for virtual networking. You can use brctl or ip commands for managing bridges and interfaces.
  5. Snapshot Management:
    • Xen doesn’t have built-in snapshot management like some other hypervisors. You can achieve similar functionality by saving the state of a VM and restoring it later.
  6. XenStore:
    • XenStore is a shared configuration database used by Xen. You can interact with it using the xenstore command. Example:perlCopy codexenstore-ls xenstore-read /local/domain/<domain_id>/memory/target
  7. Debugging and Troubleshooting:
    • xl dmesg: Display Xen hypervisor debug messages.
    • xl top: Display real-time information about the system’s virtualization.
    • xl debug-keys: Print the list of available debug key combinations.

These are some of the basic commands for managing Xen virtual machines and resources. For more detailed information and advanced usage, you can refer to the official documentation for Xen or consult the man pages for the xl command.

KVM (Kernel-based Virtual Machine) is a virtualization solution

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KVM (Kernel-based Virtual Machine) is a virtualization solution for Linux that enables users to run multiple virtual machines (VMs) on a single physical host. Below are some common command-line references for managing KVM:

  1. Creating a Virtual Machine:
    • virt-install: Command-line tool for creating new virtual machines. Example:cssCopy codevirt-install --name=myvm --memory=2048 --vcpus=2 --disk path=/var/lib/libvirt/images/myvm.qcow2,size=20 --cdrom /path/to/install.iso --network bridge=br0
  2. Managing Virtual Machines:
    • virsh: Command-line interface for managing virtual machines. Some useful commands include:
      • virsh list: List all running VMs.
      • virsh start <domain>: Start a VM.
      • virsh shutdown <domain>: Shutdown a VM gracefully.
      • virsh destroy <domain>: Forcefully shutdown a VM.
      • virsh reboot <domain>: Reboot a VM.
      • virsh suspend <domain>: Suspend a VM.
      • virsh resume <domain>: Resume a suspended VM.
  3. Managing Virtual Networks:
    • virsh net-list: List all defined virtual networks.
    • virsh net-start <network>: Start a virtual network.
    • virsh net-destroy <network>: Destroy a virtual network.
    • virsh net-edit <network>: Edit a virtual network configuration.
  4. Cloning Virtual Machines:
    • You can use virt-clone or qemu-img to clone virtual machine disk images. Example with qemu-img:cssCopy codeqemu-img create -f qcow2 -b source_image.qcow2 cloned_image.qcow2
  5. Snapshot Management:
    • virsh snapshot-create <domain>: Create a snapshot of a VM.
    • virsh snapshot-list <domain>: List snapshots of a VM.
    • virsh snapshot-revert <domain> <snapshot>: Revert a VM to a specific snapshot.
    • virsh snapshot-delete <domain> <snapshot>: Delete a snapshot of a VM.
  6. Virtual Disk Management:
    • qemu-img: Command-line tool for managing disk images. Examples:
      • qemu-img info disk_image.qcow2: Get information about a disk image.
      • qemu-img resize disk_image.qcow2 +10G: Resize a disk image.
      • qemu-img convert -f qcow2 -O raw disk_image.qcow2 disk_image.raw: Convert disk image formats.

These are some of the basic commands for managing KVM virtual machines and resources. For more detailed information and advanced usage, you can refer to the official documentation for KVM and associated tools.

The os module in Python

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The os module in Python provides a portable way to interact with the operating system, including Linux. While it doesn’t cover every aspect of Linux system administration, it offers functionalities for basic operations like file and directory manipulation, process management, and environment variables. Below are some of the key functions and classes in the os module:

  1. File and Directory Operations:
    • os.getcwd(): Get the current working directory.
    • os.chdir(path): Change the current working directory to the specified path.
    • os.listdir(path='.'): Return a list of the entries in the directory given by path.
    • os.mkdir(path): Create a directory named path.
    • os.makedirs(path): Recursive directory creation function.
    • os.remove(path): Remove (delete) the file path.
    • os.rmdir(path): Remove (delete) the directory path.
  2. Process Management:
    • os.system(command): Execute the command in a subshell.
    • os.spawn*(): Functions for spawning a new process.
    • os.fork(): Fork a child process.
    • os.kill(pid, sig): Send a signal to the process pid.
  3. Environment Variables:
    • os.environ: Dictionary containing the environment variables.
    • os.getenv(var, default=None): Get an environment variable, optionally returning a default value if the variable is not set.
  4. Miscellaneous:
    • os.path: Submodule for common pathname manipulations.
    • os.name: String representing the current operating system.
    • os.utime(path, times=None): Set the access and modified times of the file specified by path.
  5. Permissions:
    • os.chmod(path, mode): Change the mode (permissions) of path to the numeric mode.
    • os.access(path, mode): Check if a user has access to a file.

Remember, the os module provides basic functionalities. For more advanced operations, you might need to use other modules like subprocess, shutil, or os.path. Additionally, for system administration tasks on Linux, modules like subprocess, sys, shutil, socket, multiprocessing, and os.path are often used in conjunction with os.

Find and replace text within a file on Linux

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To find and replace text within a file on Linux, you can use various command-line tools such as sed, awk, or even grep combined with sed. Here’s how you can do it using sed, which is one of the most commonly used tools for this purpose:

sed -i 's/old_text/new_text/g' filename

Explanation:

  • -i: This option edits files in place. If you want to create a backup of the original file, you can use -i.bak instead, which will create a backup with the extension .bak.
  • 's/old_text/new_text/g': This is the substitution command in sed. It tells sed to substitute old_text with new_text globally (i.e., all occurrences).
  • filename: Replace this with the name of the file you want to modify.

For example, if you want to replace all occurrences of “hello” with “world” in a file named example.txt, you would use:

sed -i 's/hello/world/g' example.txt

Make sure to use caution when using the -i option, as it directly modifies the file. Always double-check the results to ensure they are as expected. If you want to preview the changes before actually modifying the file, you can omit the -i option and redirect the output to a different file:

sed 's/old_text/new_text/g' filename > new_filename

This command will perform the replacement and save the modified content to a new file called new_filename, leaving the original file unchanged.