nviz: 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/lib64/grass-6.4.4/bin/nviz - from package: grass

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

On Debian possible default full paths are:

/usr/lib/grass64/bin/nviz - from package: grass-core

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

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