mate-volume-control: 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/mate-volume-control - from package: mate-media-gstreamer
/usr/bin/mate-volume-control - from package: mate-media-pulse

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

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