ras2tiff: 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 CentOS possible default full paths are:

/usr/bin/ras2tiff - from package: libtiff

You may install the required package with command yum install {package}

On Debian possible default full paths are:

/usr/bin/ras2tiff - from package: libtiff-tools

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

Error in other languages:
ras2tiff: bevel nie gevind nie
ras2tiff: comandă negăsită
ras2tiff: comando não encontrado
ras2tiff: commande introuvable
ras2tiff: command not found
ras2tiff: käsku ei ole
ras2tiff: không tìm thấy lệnh
ras2tiff: komanda nerasta
ras2tiff: Kommando nicht gefunden.
ras2tiff: kommandot finns inte
ras2tiff: komut yok
ras2tiff: nie znaleziono polecenia
ras2tiff: níor aimsíodh an t-ordú
ras2tiff: no se encontró la orden
ras2tiff: no s'ha trobat l'ordre
ras2tiff: opdracht niet gevonden
ras2tiff: parancs nem található
ras2tiff: perintah tidak ditemukan
ras2tiff: príkaz nenájdený
ras2tiff: příkaz nenalezen
ras2tiff: команда не найдена
ras2tiff: командата не е открита
ras2tiff: 命令找不到
ras2tiff: コマンドが見つかりません