In UNIX the following commands are present:

halt --poweroff     //does poweroff
halt --reboot       //does reboot
poweroff --reboot   //does reboot
reboot --poweroff   //does poweroff

However the following three simple commands do the same job


So what is the necessity of such commands

  • 3
    I think you forgot shutdown -h now and shutdown -r now as well. – KevinO Jun 22 '17 at 15:03
  • Which Unix specifically? – muru Jun 22 '17 at 15:33
  • I guess these commands apply in all flavors uniformly – shiningstar Jun 22 '17 at 15:36
  • It was (and is) also common to invoke one particular command under different names using links, and the same effect can usually be achieved using the original name and options. – dirkt Jun 22 '17 at 18:52

The answer to our question is more or less: History!

Those are typically symlinks to the same binary. On systems using systemd often to systemctl, on an older system I just checked reboot and poweroff are symlinks to halt.

There are systems out there where halt and poweroff doesn't do the same thing, in that halt stops the OS, leaving the machine running with whatever environment the hardware offers, while poweroff does what it says and makes the machine stop consuming power. (It should be obvious that reboot is a third operation).

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