gxmms2: 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/gxmms2 - from package: gxmms2

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

Error in other languages:
gxmms2: bevel nie gevind nie
gxmms2: comandă negăsită
gxmms2: comando não encontrado
gxmms2: commande introuvable
gxmms2: command not found
gxmms2: käsku ei ole
gxmms2: không tìm thấy lệnh
gxmms2: komanda nerasta
gxmms2: Kommando nicht gefunden.
gxmms2: kommandot finns inte
gxmms2: komut yok
gxmms2: nie znaleziono polecenia
gxmms2: níor aimsíodh an t-ordú
gxmms2: no se encontró la orden
gxmms2: no s'ha trobat l'ordre
gxmms2: opdracht niet gevonden
gxmms2: parancs nem található
gxmms2: perintah tidak ditemukan
gxmms2: príkaz nenájdený
gxmms2: příkaz nenalezen
gxmms2: команда не найдена
gxmms2: командата не е открита
gxmms2: 命令找不到
gxmms2: コマンドが見つかりません