vtk: 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/vtk - from package: vtk-tcl

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

On Debian possible default full paths are:

/usr/bin/vtk - from package: tcl-vtk

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

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