radeonreg: 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 Debian possible default full paths are:

/usr/sbin/radeonreg - from package: radeontool

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

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