dnspktflow: 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/dnspktflow - from package: dnssec-tools

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

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