out123: 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/out123 - from package: mpg123

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

Error in other languages:
out123: bevel nie gevind nie
out123: comandă negăsită
out123: comando não encontrado
out123: commande introuvable
out123: command not found
out123: käsku ei ole
out123: không tìm thấy lệnh
out123: komanda nerasta
out123: Kommando nicht gefunden.
out123: kommandot finns inte
out123: komut yok
out123: nie znaleziono polecenia
out123: níor aimsíodh an t-ordú
out123: no se encontró la orden
out123: no s'ha trobat l'ordre
out123: opdracht niet gevonden
out123: parancs nem található
out123: perintah tidak ditemukan
out123: príkaz nenájdený
out123: příkaz nenalezen
out123: команда не найдена
out123: командата не е открита
out123: 命令找不到
out123: コマンドが見つかりません