mpg123.bin: 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/mpg123.bin - from package: mpg123

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

Error in other languages:
mpg123.bin: bevel nie gevind nie
mpg123.bin: comandă negăsită
mpg123.bin: comando não encontrado
mpg123.bin: commande introuvable
mpg123.bin: command not found
mpg123.bin: käsku ei ole
mpg123.bin: không tìm thấy lệnh
mpg123.bin: komanda nerasta
mpg123.bin: Kommando nicht gefunden.
mpg123.bin: kommandot finns inte
mpg123.bin: komut yok
mpg123.bin: nie znaleziono polecenia
mpg123.bin: níor aimsíodh an t-ordú
mpg123.bin: no se encontró la orden
mpg123.bin: no s'ha trobat l'ordre
mpg123.bin: opdracht niet gevonden
mpg123.bin: parancs nem található
mpg123.bin: perintah tidak ditemukan
mpg123.bin: príkaz nenájdený
mpg123.bin: příkaz nenalezen
mpg123.bin: команда не найдена
mpg123.bin: командата не е открита
mpg123.bin: 命令找不到
mpg123.bin: コマンドが見つかりません