hard-reboot: command not found

Maybe Your $PATH variable doesn't contain the default paths? echo $PATH should give something like:

[root@server ~]# echo $PATH
/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin

If it's empty, You may set the PATH variable with this command

export PATH="/usr/local/sbin:/usr/local/bin:/sbin:/bin:/usr/sbin:/usr/bin:/root/bin"

On Debian possible default full paths are:

/sbin/hard-reboot - from package: minit

You may install the required package with command apt-get install {package}

Error in other languages:
hard-reboot: bevel nie gevind nie
hard-reboot: comandă negăsită
hard-reboot: comando não encontrado
hard-reboot: commande introuvable
hard-reboot: command not found
hard-reboot: käsku ei ole
hard-reboot: không tìm thấy lệnh
hard-reboot: komanda nerasta
hard-reboot: Kommando nicht gefunden.
hard-reboot: kommandot finns inte
hard-reboot: komut yok
hard-reboot: nie znaleziono polecenia
hard-reboot: níor aimsíodh an t-ordú
hard-reboot: no se encontró la orden
hard-reboot: no s'ha trobat l'ordre
hard-reboot: opdracht niet gevonden
hard-reboot: parancs nem található
hard-reboot: perintah tidak ditemukan
hard-reboot: príkaz nenájdený
hard-reboot: příkaz nenalezen
hard-reboot: команда не найдена
hard-reboot: командата не е открита
hard-reboot: 命令找不到
hard-reboot: コマンドが見つかりません