Crack: 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 CentOS possible default full paths are:

/usr/bin/Crack - from package: crack

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/sbin/Crack - from package: crack-md5
/usr/sbin/Crack - from package: crack

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

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