tviewer: 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/tviewer - from package: python-mmtk

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

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