g.rename: 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/g.rename - 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/g.rename - from package: grass-core

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

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