Locking Consoles and Virtual Terminals with physlock (with examples)

Lock every console (require current user or root to unlock):

physlock

Motivation: This use case allows you to lock all consoles and virtual terminals. When executed, it will prompt you for a password and lock all consoles and virtual terminals, preventing unauthorized access to the system.

Explanation: By simply running the physlock command without any arguments, it will lock all consoles and virtual terminals. The physlock command requires the current user or root to unlock, ensuring that only authorized users can regain access to the system.

Example Output: After executing the physlock command, the screen will be locked, and you will be prompted for a password. Until the correct password is entered, the consoles and virtual terminals will remain locked.

Mute kernel messages on console while locked:

physlock -m

Motivation: When the system is locked, it is desirable to mute any kernel messages to prevent potentially sensitive information from being displayed on the screen. This use case ensures that no kernel messages are shown while the system is locked.

Explanation: The -m option is used with the physlock command to mute the kernel messages on the console while the system is locked. It suppresses any kernel messages, preventing them from being displayed on the screen while the system is locked.

Example Output: After executing the physlock -m command, the system will be locked, and no kernel messages will be displayed on the console. Only the password prompt will be visible.

Disable SysRq mechanism while locked:

physlock -s

Motivation: The SysRq mechanism is a key combination that can send various low-level commands to the Linux kernel. By disabling the SysRq mechanism while the system is locked, you can prevent any potential misuse or unauthorized access to sensitive system functions.

Explanation: The -s option is used with the physlock command to disable the SysRq mechanism while the system is locked. When executed, it prevents any low-level commands from being sent to the Linux kernel via the SysRq key combination while the system is locked.

Example Output: After executing the physlock -s command, the system will be locked, and any attempts to invoke low-level commands using the SysRq key combination will be ineffective.

Display a message before the password prompt:

physlock -p "Locked!"

Motivation: Adding a custom message before the password prompt can provide additional information or instructions to the user before they enter the password. It can also serve as a reminder or a warning for the user.

Explanation: The -p option is used with the physlock command to display a custom message before the password prompt. By providing a message enclosed in double quotes after the -p option, the specified message will be shown on the screen before the password prompt when the system is locked.

Example Output: After executing the physlock -p "Locked!" command, the system will be locked, and the message “Locked!” will be displayed on the screen before the password prompt.

Fork and detach physlock (useful for suspend or hibernate scripts):

physlock -d

Motivation: In certain situations, such as when using suspend or hibernate scripts, it may be necessary to fork and detach the physlock command so that it can continue running in the background without blocking other processes.

Explanation: The -d option is used with the physlock command to fork and detach it from the current process. This allows physlock to continue running in the background without blocking other processes. It is particularly useful in scenarios where a system needs to be locked but still able to execute other commands or scripts.

Example Output: After executing the physlock -d command, the system will be locked, and physlock will continue running in the background, allowing other processes or scripts to be executed without being blocked by the lock.