How to use the command 'vgscan' (with examples)

The vgscan command is part of the Logical Volume Manager (LVM) suite in Linux-based systems, which facilitates the management of disk storage across several physical volumes. Specifically, vgscan is used to search for and list volume groups (VGs) on all supported LVM block devices. This command is crucial for system administrators and users looking to manage, modify, or inspect the logical volumes within their systems, as it provides a gateway to identify and manipulate the underlying volume groups.

Use case 1: Scanning for Volume Groups and Displaying Information

Code:

sudo vgscan

Motivation:

Running the sudo vgscan command is essential when a user needs to verify the existence and state of volume groups in their system. This action is significant when configuring a new LVM setup, performing system diagnostics, or after reattaching storage devices. By scanning for volume groups, users can ensure that all logical volumes are recognized and are ready for access or modifications.

Explanation:

• sudo: This is used to run the command with superuser privileges. Modifying or accessing volume groups requires elevated permissions, as they are critical components of system storage.
• vgscan: This command scans all available block devices in the system supported by LVM to locate any existing groups. It gives a report on the existing volume groups, which is helpful for further configurations or verifications.

Example Output:

  Reading all physical volumes. This may take a while...
  Found volume group "vg1" using metadata type lvm2
  Found volume group "vg2" using metadata type lvm2

This output informs the user that two volume groups, “vg1” and “vg2”, have been successfully found, ensuring the system’s logical volume resources are accessible.

Use case 2: Scanning and Creating Node Files for Logical Volumes

Code:

sudo vgscan --mknodes

Motivation:

The sudo vgscan --mknodes command is used when there is a need to access logical volumes, but necessary node files in the /dev directory are missing. This situation may arise during system recovery, after hardware changes, or following disk or node configuration removals. By generating these node files, users ensure that logical volumes can be mounted and accessed correctly, allowing for data management and application continuity.

Explanation:

• sudo: Similar to the previous use case, sudo is necessary to gain the required permissions for system changes.
• vgscan: Scans and identifies existing volume groups on all available LVM-compatible devices.
• --mknodes: This option tells vgscan to create the necessary device node files within the /dev directory if they do not already exist. These files are crucial for the kernel to interface with the logical volumes correctly.

Example Output:

  Reading all physical volumes. This may take a while...
  Found volume group "vg1" using metadata type lvm2
  Found volume group "vg2" using metadata type lvm2
  Creating volume group node files

This output summarizes the procedure: locating existing volume groups and creating the necessary node files to point to logical volumes. It indicates a successful configuration for user access and system management.

Conclusion

The vgscan command is a vital tool in the LVM toolkit, offering system administrators and Linux users a robust method to identify, verify, and prepare volume groups for use. Whether for initialization, diagnostics, or system recovery, its functionality ensures that logical volumes are accurately recognized and ready for management. Understanding the application of vgscan in various contexts enables users to efficiently handle LVM environments, safeguarding data integrity and system performance.