nixpkgs/nixos/doc/manual/administration/rebooting.chapter.md

Rebooting and Shutting Down

The system can be shut down (and automatically powered off) by doing:

# shutdown

This is equivalent to running systemctl poweroff.

To reboot the system, run

# reboot

which is equivalent to systemctl reboot. Alternatively, you can quickly reboot the system using kexec, which bypasses the BIOS by directly loading the new kernel into memory:

# systemctl kexec

The machine can be suspended to RAM (if supported) using systemctl suspend, and suspended to disk using systemctl hibernate.

These commands can be run by any user who is logged in locally, i.e. on a virtual console or in X11; otherwise, the user is asked for authentication.