nsd-checkconf: 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/nsd-checkconf - from package: nsd

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

On Debian possible default full paths are:

/usr/sbin/nsd-checkconf - from package: nsd

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

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