unable to restart dhcp with CLI

[ewok2]

Hello

I would like to renew my dhcp lease by using external script with ssh (It work fine when I use the HMI).
But when in a console I try type :

restartservice dhclient restart em0

I get

'em0' is not a DHCP-enabled interface
dhclient already running?  (pid=8209).

my WAN interface is em0 and is configure in dhcp...
when I do :

less /var/db/dhclient.leases.em0

I get the informations.

Any Idea of my probleme?
thanks