ns_to_db: 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/ns_to_db - from package: perl-Fsdb

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

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