rtmpdump: 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/rtmpdump - from package: rtmpdump

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

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