mgdiff: 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/mgdiff - from package: mgdiff

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

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