vdiff: 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/vdiff - from package: atfs

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

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