quodlibet: 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/quodlibet - from package: quodlibet

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

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