genkrf: command not found

Have You tried accessing the binary with the full path?

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/genkrf - from package: dnssec-tools

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