ldns-version: 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/ldns-version - from package: ldns

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

On Debian possible default full paths are:

/usr/bin/ldns-version - from package: ldnsutils

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

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