grass: 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/grass - from package: grass

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

On Debian possible default full paths are:

/usr/bin/grass - from package: grass-core

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

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