lnewusers: 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/lnewusers - from package: libuser

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

On Debian possible default full paths are:

/usr/sbin/lnewusers - from package: libuser

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

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