dpl4hydra: 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/dpl4hydra - from package: hydra

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

Error in other languages:
dpl4hydra: bevel nie gevind nie
dpl4hydra: comandă negăsită
dpl4hydra: comando não encontrado
dpl4hydra: commande introuvable
dpl4hydra: command not found
dpl4hydra: käsku ei ole
dpl4hydra: không tìm thấy lệnh
dpl4hydra: komanda nerasta
dpl4hydra: Kommando nicht gefunden.
dpl4hydra: kommandot finns inte
dpl4hydra: komut yok
dpl4hydra: nie znaleziono polecenia
dpl4hydra: níor aimsíodh an t-ordú
dpl4hydra: no se encontró la orden
dpl4hydra: no s'ha trobat l'ordre
dpl4hydra: opdracht niet gevonden
dpl4hydra: parancs nem található
dpl4hydra: perintah tidak ditemukan
dpl4hydra: príkaz nenájdený
dpl4hydra: příkaz nenalezen
dpl4hydra: команда не найдена
dpl4hydra: командата не е открита
dpl4hydra: 命令找不到
dpl4hydra: コマンドが見つかりません