weak-modules: 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:

/sbin/weak-modules - from package: module-init-tools

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

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