nsupdate: 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/bin/nsupdate - from package: bind-utils

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

On Debian possible default full paths are:

/usr/bin/nsupdate - from package: dnsutils
/usr/bin/nsupdate - from package: knot-dnsutils

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

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