ddv: 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/ddv - from package: ncbi-tools-x11

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

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