dvgrab: 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/dvgrab - from package: dvgrab

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

On Debian possible default full paths are:

/usr/bin/dvgrab - from package: dvgrab

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

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