nsec3dig: 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/nsec3dig - from package: pdns-tools

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

Error in other languages:
nsec3dig: bevel nie gevind nie
nsec3dig: comandă negăsită
nsec3dig: comando não encontrado
nsec3dig: commande introuvable
nsec3dig: command not found
nsec3dig: käsku ei ole
nsec3dig: không tìm thấy lệnh
nsec3dig: komanda nerasta
nsec3dig: Kommando nicht gefunden.
nsec3dig: kommandot finns inte
nsec3dig: komut yok
nsec3dig: nie znaleziono polecenia
nsec3dig: níor aimsíodh an t-ordú
nsec3dig: no se encontró la orden
nsec3dig: no s'ha trobat l'ordre
nsec3dig: opdracht niet gevonden
nsec3dig: parancs nem található
nsec3dig: perintah tidak ditemukan
nsec3dig: príkaz nenájdený
nsec3dig: příkaz nenalezen
nsec3dig: команда не найдена
nsec3dig: командата не е открита
nsec3dig: 命令找不到
nsec3dig: コマンドが見つかりません