music123: 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/music123 - from package: music123

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

Error in other languages:
music123: bevel nie gevind nie
music123: comandă negăsită
music123: comando não encontrado
music123: commande introuvable
music123: command not found
music123: käsku ei ole
music123: không tìm thấy lệnh
music123: komanda nerasta
music123: Kommando nicht gefunden.
music123: kommandot finns inte
music123: komut yok
music123: nie znaleziono polecenia
music123: níor aimsíodh an t-ordú
music123: no se encontró la orden
music123: no s'ha trobat l'ordre
music123: opdracht niet gevonden
music123: parancs nem található
music123: perintah tidak ditemukan
music123: príkaz nenájdený
music123: příkaz nenalezen
music123: команда не найдена
music123: командата не е открита
music123: 命令找不到
music123: コマンドが見つかりません