krfcheck: 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/krfcheck - from package: dnssec-tools

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

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