lusermod: 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/sbin/lusermod - from package: libuser

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

On Debian possible default full paths are:

/usr/sbin/lusermod - from package: libuser

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

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