How to Use the Command 'virsh connect' (with Examples)

The virsh connect command is a versatile tool used to establish a connection to a virtual machine hypervisor. This tool is part of the Virtual Machine Manager (virt-manager) suite and is primarily used in virtualization environments where system administrators manage and maintain multiple virtual machines. virsh connect allows users to interact with the hypervisor in various ways, providing access as a local user or remotely, and both securely and flexibly. Below, we delve into specific use cases and examples to demonstrate the power and utility of the virsh connect command.

Use Case 1: Connect to the Default Hypervisor

Code:

virsh connect

Motivation: Connecting to the default hypervisor is a common task for users who need to perform routine management and monitoring of their virtual machines. This command is especially useful for those who prefer a straightforward method without the need to specify additional parameters, making it an ideal choice for beginners or for environments where the default settings are already properly configured.

Explanation: The command virsh connect with no additional arguments uses the system’s default hypervisor configuration. By default, it uses the user’s session to establish the connection, providing a quick and easy way to start managing virtual machines. This assumes the hypervisor is locally accessible and pre-configured to suit the user’s environment.

Example Output:

Welcome to virsh, the virtualization interactive terminal.

Type:  'help' for help with commands
       'quit' to quit

virsh # 

Use Case 2: Connect as Root to the Local QEMU/KVM Hypervisor

Code:

virsh connect qemu:///system

Motivation: There are occasions when an administrator needs enhanced permissions to manage a virtual machine hypervisor. Accessing the hypervisor as the root user allows for full administrative access to all virtual machines and configuration settings. This is crucial for tasks that require elevated privileges like creating, deleting, or altering virtual machine configurations.

Explanation:

• qemu indicates the use of the QEMU hypervisor, which is commonly paired with KVM for running virtual machines.
• system signifies the system-wide hypervisor context, as opposed to a user session, providing elevated access rights.

Example Output:

Connected to the local hypervisor running QEMU/KVM with system permissions
Welcome to virsh, the virtualization interactive terminal.
Type:  'help' for help with commands
       'quit' to quit

virsh # 

Use Case 3: Launch a New Instance of the Hypervisor and Connect as the Local User

Code:

virsh connect qemu:///session

Motivation: This scenario is ideal for users who need a private instance of the hypervisor, such as for development or testing purposes. A session-based connection allows managing VMs within the user’s session without affecting the system-wide settings, thereby reducing risk and safeguarding changes to other virtual machines running on the host.

Explanation:

• qemu specifies the hypervisor in use.
• session signals a user-specific session context, which confines actions and changes to the user’s personal environment.

Example Output:

Connected to a user-sessioned instance of the QEMU hypervisor.
Welcome to virsh, the virtualization interactive terminal.
Type:  'help' for help with commands
       'quit' to quit

virsh # 

Use Case 4: Connect as Root to a Remote Hypervisor Using SSH

Code:

virsh connect qemu+ssh://user_name@host_name/system

Motivation: Remote connections are vital for administrators who manage virtual environments spread across different physical locations or data centers. Using SSH provides a secure channel for connecting to the hypervisor remotely, ensuring data and actions are encrypted and protected from unauthorized access or eavesdropping.

Explanation:

• qemu signifies the type of hypervisor being accessed.
• ssh specifies that the connection should be made using SSH protocol for security.
• user_name denotes the username used to authenticate on the remote host.
• host_name is the hostname or IP address of the remote machine where the hypervisor runs.
• system allows connection to the system-based hypervisor, providing access to all its managerial features remotely.

Example Output:

Connecting to remote hypervisor on host_name using SSH...
Key fingerprint is SHA256:[fingerprint]
Are you sure you want to continue connecting (yes/no)? yes
[user_name@host_name's password: [password]]

Connected to the remote system hypervisor.
Welcome to virsh, the virtualization interactive terminal.
Type:  'help' for help with commands
       'quit' to quit

virsh # 

Conclusion

The virsh connect command is a powerful utility that provides flexible options for connecting to both local and remote virtual machine hypervisors. With the ability to adjust permissions, launch session-based environments, and secure remote connections via SSH, virsh connect is an indispensable tool for systems administrators and developers working in virtualized environments. By understanding and utilizing these use cases, users can greatly enhance their virtualization management workflows.