dh_dkms: 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/dh_dkms - from package: dkms

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

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