nl-cls-add: 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/nl-cls-add - from package: libnl3-cli

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

On Debian possible default full paths are:

/usr/sbin/nl-cls-add - from package: libnl-utils

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

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