install-mbr: 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:

/sbin/install-mbr - from package: mbr

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

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