cvsmgdiff: 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/cvsmgdiff - from package: mgdiff

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

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