cf-know: 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/sbin/cf-know - from package: cfengine

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

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