rmgdiff: 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/rmgdiff - from package: mgdiff

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

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