dnssec-checkds: 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 Debian possible default full paths are:

/usr/sbin/dnssec-checkds - from package: bind9utils

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

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