rhythmbox: 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 CentOS possible default full paths are:

/usr/bin/rhythmbox - from package: rhythmbox

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/rhythmbox - from package: rhythmbox

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

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