halt, poweroff, reboot — Halt, power-off or reboot the machine
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:
Halt the machine, regardless of which one of the three commands is invoked.
Power-off the machine, when either halt or poweroff is invoked. This option is ignored when reboot is invoked.
Reboot the machine, regardless of which one of the three commands is invoked.
Force immediate halt, power-off, reboot. If specified, the command does not contact the init system. In most cases, filesystems are not properly unmounted before shutdown. For example, the command reboot -f is mostly equivalent to systemctl reboot -ff, instead of systemctl reboot -f.
Only write wtmp shutdown entry, do not actually halt, power-off, reboot.
Do not write wtmp shutdown entry.
Don't 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.