rdf2dot: 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/rdf2dot - from package: python-rdflib-tools

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

Error in other languages:
rdf2dot: bevel nie gevind nie
rdf2dot: comandă negăsită
rdf2dot: comando não encontrado
rdf2dot: commande introuvable
rdf2dot: command not found
rdf2dot: käsku ei ole
rdf2dot: không tìm thấy lệnh
rdf2dot: komanda nerasta
rdf2dot: Kommando nicht gefunden.
rdf2dot: kommandot finns inte
rdf2dot: komut yok
rdf2dot: nie znaleziono polecenia
rdf2dot: níor aimsíodh an t-ordú
rdf2dot: no se encontró la orden
rdf2dot: no s'ha trobat l'ordre
rdf2dot: opdracht niet gevonden
rdf2dot: parancs nem található
rdf2dot: perintah tidak ditemukan
rdf2dot: príkaz nenájdený
rdf2dot: příkaz nenalezen
rdf2dot: команда не найдена
rdf2dot: командата не е открита
rdf2dot: 命令找不到
rdf2dot: コマンドが見つかりません