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 CentOS possible default full paths are:

/usr/sbin/dkms - from package: dkms

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

On Debian possible default full paths are:

/usr/sbin/dkms - from package: dkms

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

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