greytiff: 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/greytiff - from package: argyll

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

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