ophcrack: 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:

/usr/bin/ophcrack - from package: ophcrack

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

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