newusers: 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/newusers - from package: shadow-utils

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

On Debian possible default full paths are:

/usr/sbin/newusers - from package: passwd

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

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