tvtk_doc: 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/tvtk_doc - from package: Mayavi

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

On Debian possible default full paths are:

/usr/bin/tvtk_doc - from package: mayavi2

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

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