mtp: 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/mtp - from package: ferret-vis

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

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