dt-validate: 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/dt-validate - from package: dnssec-tools

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

On Debian possible default full paths are:

/usr/bin/dt-validate - from package: libval-bin

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

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