ctrlaltdel

Get current setting

$ ctrlaltdel

$ sudo ctrlaltdel hard

$ sudo ctrlaltdel soft

ctrlaltdel [hard|soft]

ctrlaltdel controls the kernel's behavior when Ctrl+Alt+Del is pressed on the console. The setting determines whether the system reboots immediately or allows processes to shut down gracefully.
With "hard", the system reboots immediately. With "soft", SIGINT is sent to PID 1 (init/systemd), which handles a graceful shutdown.

hard

Reboot immediately without preparation

Send SIGINT to init for graceful reboot

Requires root privileges to change the setting. Part of util-linux. On modern systemd systems, systemd handles the Ctrl+Alt+Del signal regardless of this setting.

This control exists from early Unix days when physical console access was common. The three-key combination was chosen to be difficult to press accidentally.

reboot(8), shutdown(8), systemctl(1)