john: command not found

Have You tried accessing the binary with the full path?

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/sbin/john - from package: john

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