rygel-preferences: 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/rygel-preferences - from package: rygel-preferences

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

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