dfbpenmount: 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/dfbpenmount - from package: directfb

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

On Debian possible default full paths are:

/usr/bin/dfbpenmount - from package: libdirectfb-bin

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

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