hdhomerun_config_gui: 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/hdhomerun_config_gui - from package: hdhomerun

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

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