dvbctrl: 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/bin/dvbctrl - from package: dvbstreamer

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

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