How to use the command 'virsh' (with examples)
The ‘virsh’ command is a management tool for controlling virsh guest domains, allowing the user to perform various operations such as connecting to a hypervisor session, listing domains, creating, editing, and deleting guests, as well as saving and restoring their state. This article will provide examples of each use case to illustrate how to use the ‘virsh’ command effectively.
Use case 1: Connect to a hypervisor session
Code:
virsh connect qemu:///system
Motivation: Connecting to a hypervisor session allows the user to manage virtual machines and access their details and metrics. It is useful in scenarios where the user needs to monitor or modify the configuration of the virtual machine.
Explanation:
virsh: The command to manage virsh guest domains.connect: Subcommand to establish a connection to the hypervisor.qemu:///system: URI specifying the type and location of the hypervisor. In this example, ‘qemu’ refers to the QEMU/KVM hypervisor, and ‘system’ indicates the local system.
Example output: No output will be displayed if the connection is successful. If there is an error, an appropriate error message will be shown.
Use case 2: List all domains
Code:
virsh list --all
Motivation: Listing all domains provides an overview of the available virtual machines and their current state. It helps the user to identify running, paused, and shutdown domains, along with their associated details such as ID, name, and status.
Explanation:
virsh: The command to manage virsh guest domains.list: Subcommand to list domains.--all: Option to show all domains, including those that are shut down or in a paused state.
Example output:
Id Name State
----------------------------------------------------
1 domain1 running
2 domain2 paused
3 domain3 shut off
Use case 3: Dump guest configuration file
Code:
virsh dumpxml guest_id > path/to/guest.xml
Motivation: Dumping the guest configuration file allows the user to extract the XML representation of the guest’s configuration. This can be helpful for backup, migration, or troubleshooting purposes.
Explanation:
virsh: The command to manage virsh guest domains.dumpxml: Subcommand to retrieve the XML dump of a guest’s configuration.guest_id: The ID, name, or UUID of the guest for which the configuration needs to be dumped.> path/to/guest.xml: Redirection operator to save the XML dump in the specified path.
Example output: No output will be displayed if the command executes successfully. The guest’s configuration XML will be saved in the specified path (‘path/to/guest.xml’).
Use case 4: Create a guest from a configuration file
Code:
virsh create path/to/config_file.xml
Motivation: Creating a guest from a configuration file allows the user to define and deploy guests with pre-configured settings. This saves time and ensures consistency in the deployment process, as the same configuration can be used to reproduce the guest.
Explanation:
virsh: The command to manage virsh guest domains.create: Subcommand to create a guest from a configuration file.path/to/config_file.xml: The path to the XML file containing the configuration for the guest.
Example output: No output will be displayed if the guest creation is successful. If there is an error in the XML file or the guest cannot be created, an appropriate error message will be shown.
Use case 5: Edit a guest’s configuration file
Code:
virsh edit guest_id
Motivation: Editing a guest’s configuration file allows the user to modify the guest’s settings, such as CPU, memory, device attachments, and more. It provides flexibility and control over the configuration to meet specific requirements.
Explanation:
virsh: The command to manage virsh guest domains.edit: Subcommand to open the guest’s configuration file in the default text editor (can be changed with $EDITOR environment variable).guest_id: The ID, name, or UUID of the guest whose configuration needs to be edited.
Example output: The configuration file will be opened in the default text editor. Any changes made and saved in the editor will be reflected in the guest’s configuration.
Use case 6: Start/reboot/shutdown/suspend/resume a guest
Code:
virsh command guest_id
Motivation: Performing various operations like starting, rebooting, shutting down, suspending, and resuming a guest allows the user to control the state and behavior of the virtual machine. It is useful for managing the lifecycle of the guest according to the desired requirements.
Explanation:
virsh: The command to manage virsh guest domains.command: Specific operation to be performed on the guest, such as ‘start’, ‘reboot’, ‘shutdown’, ‘suspend’, or ‘resume’.guest_id: The ID, name, or UUID of the guest on which the operation needs to be performed.
Example output: No output will be displayed if the command executes successfully. If there is an error or the command cannot be executed on the guest, an appropriate error message will be shown.
Use case 7: Save the current state of a guest to a file
Code:
virsh save guest_id filename
Motivation: Saving the current state of a guest to a file allows the user to capture its exact state at a specific point in time. This can be useful for migration, backup, or restoring purposes.
Explanation:
virsh: The command to manage virsh guest domains.save: Subcommand to save the current state of a guest.guest_id: The ID, name, or UUID of the guest to be saved.filename: The name of the file in which the guest’s state will be saved.
Example output: No output will be displayed if the command executes successfully. If there is an error or the guest’s state cannot be saved, an appropriate error message will be shown.
Use case 8: Delete a running guest
Code:
virsh destroy guest_id && virsh undefine guest_id
Motivation: Deleting a running guest allows the user to completely remove the guest from the hypervisor. This is useful when the guest is no longer needed or needs to be reconfigured from scratch.
Explanation:
virsh: The command to manage virsh guest domains.destroy: Subcommand to forcibly terminate a running guest by shutting it down.guest_id: The ID, name, or UUID of the guest to be destroyed.undefine: Subcommand to undefine the guest from the hypervisor, removing its configuration entirely.
Example output: No output will be displayed if the command executes successfully. If there is an error or the guest cannot be destroyed and undefined, an appropriate error message will be shown.
Conclusion:
The ‘virsh’ command provides a comprehensive set of functionalities to manage virsh guest domains. With these examples, users can effectively utilize the ‘virsh’ command to connect to hypervisor, list domains, create, edit, delete guests, and manage their state. By understanding the different use cases and their associated commands and arguments, users can efficiently navigate and control virtualized environments.
