How to use the command 'dm-tool' (with examples)

The dm-tool command is an essential utility for managing display sessions, offering seamless communication with the display manager. It is particularly beneficial in environments running LightDM, a common display manager for Linux desktop environments. The command allows users to switch sessions, lock screens, and manage seats dynamically, enhancing both security and usability. Below, we examine several specific use cases for the dm-tool command, showcasing its versatility and potential applications.

Use case 1: Show the greeter while keeping current desktop session open

Code:

dm-tool switch-to-greeter

Motivation:

In a shared computer environment, it’s often necessary to provide access to new users without disrupting the ongoing activities of a current session. The dm-tool switch-to-greeter command is helpful here because it opens the display manager’s greeter screen, allowing other users to log in while keeping the current user’s session active and safe in the background. This is perfect for multi-user workstations or family computers where session privacy and continuity are crucial.

Explanation:

• switch-to-greeter: This argument commands the display manager to show the login screen (greeter) while the current session remains logged in and intact.

Example Output:

Upon executing this command, the screen will transition to the login greeter, offering a selection of user accounts available on the system. Current applications and processes will remain open and unaltered in the background, ensuring a smooth transition back to the original session after authentication.

Use case 2: Lock the current session

Code:

dm-tool lock

Motivation:

Locking your session is a straightforward but effective method to safeguard your work from unauthorized access. By using dm-tool lock, you can instantly ensure that your desktop environment is protected, only allowing access again to the authenticated user. This is essential in any workspace where leaving your computer unattended might pose a security risk.

Explanation:

• lock: This simple command argument instructs the display manager to secure the session by prompting the screen lock, requiring user re-authentication for access.

Example Output:

Executing this command will immediately display your screen locking UI, which typically requires the current user’s password to unlock and enter back into the session. In systems with configured lock screens, a basic lock interface or customized lock application appears.

Use case 3: Switch to a specific user, showing an authentication prompt if required

Code:

dm-tool switch-to-user username session

Motivation:

In environments where multiple users need to access their accounts on the same machine concurrently, fluidly moving from one user’s session to another is critical. This command is particularly useful as it allows a seamless transition between user sessions without logging out or interrupting others’ work.

Explanation:

• switch-to-user: Directs the command towards switching active sessions.
• username: Placeholder for the actual username you want to switch to. This user must have a session available on the system.
• session: Refers to the specific session environment (like GNOME, KDE) the user is operating under. It ensures that upon switching, the correct desktop environment is launched.

Example Output:

Utilizing this command switches the session to the specified user’s desktop environment. If the user’s session is not currently active, a login prompt will appear, requesting authentication. Once authenticated, the display switches directly to that user’s workspace.

Use case 4: Add a dynamic seat from within a running LightDM session

Code:

dm-tool add-seat xlocal name=value

Motivation:

This capability is highly advantageous in environments where hardware resources are shared across various setups, such as exhibition spaces, libraries, or labs. Adding a dynamic seat via the dm-tool add-seat within an active session means you can reconfigure and organize new display setups without restarting the LightDM service, thereby minimizing disruptions.

Explanation:

• add-seat: Initiates the addition of a seat, which essentially is a set of resources allocated to manage user sessions (input devices, screens).
• xlocal: This argument specifies the type of backend the new seat uses, in this context signifying the local management of sessions within the current X server.
• name=value: A generic placeholder indicating any set of key-value pairs that will define the characteristics of the newly created seat (often used to specify further configuration details).

Example Output:

Upon command execution, a new seat is added dynamically, accommodating another user environment with its input device and screen allocation. No immediate visible output occurs unless errors arise, but in backend operations, a new seat symbolically becomes available for session handling and user management.

Conclusion:

The dm-tool command offers potent functionalities for managing session security and user transition in Linux environments. Whether needing to secure a session, manage multiple users seamlessly, or dynamically allocate resources, dm-tool provides efficient methods to navigate and manage display effectively.