dvdbackup: 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/dvdbackup - from package: dvdbackup

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

On Debian possible default full paths are:

/usr/bin/dvdbackup - from package: dvdbackup

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

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