krfb: 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/krfb - from package: kdenetwork

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

On Debian possible default full paths are:

/usr/bin/krfb - from package: krfb

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

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