mumble-overlay: 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/mumble-overlay - from package: mumble

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

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