reboot or enable/disable Ctrl-Alt-Del
Reboot the system
Power off the system (same as poweroff)
Halt the system (same as halt)
Reboot immediately without contacting the system manager
Write the wtmp shutdown entry without rebooting the system
halt, poweroff, reboot may be used to halt, power-off, or reboot the machine. All three commands take the same options.
The following options are understood:
Print a short help text and exit.
Halt the machine, regardless of which one of the three commands is invoked.
Power-off the machine, regardless of which one of the three commands is invoked.
Reboot the machine, regardless of which one of the three commands is invoked.
Force immediate halt, power-off, reboot. Do not contact the init system.
Only write wtmp shutdown entry, do not actually halt, power-off, reboot.
Do not write wtmp shutdown entry.
Dont sync hard disks/storage media before halt, power-off, reboot.
Do not send wall message before halt, power-off, reboot.
On success, 0 is returned, a non-zero failure code otherwise.
These commands are implemented in a way that preserves basic compatibility with the original SysV commands. systemctl(1) verbs halt, poweroff, reboot provide the same functionality with some additional features.
Note that on many SysV systems halt used to be synonymous to poweroff, i.e. both commands would equally result in powering the machine off. systemd is more accurate here, and halt results in halting the machine only (leaving power on), and poweroff is required to actually power it off.