Why dhclient is still running when I choose static IP?

Question

I modify dhcp to static in /etc/network/interfaces (like below).

# The primary network interface
auto eth0
iface eth0 inet static
netmask 255.255.0.0
address 10.10.130.128
gateway 10.10.1.1

Then restart the interface.

$ sudo ifdown eth0; sudo ifup eth0
...
$ ifconfig
eth0      Link encap:Ethernet 
          inet addr:10.10.130.128  Bcast:10.10.255.255  Mask:255.255.0.0

So the new address kicks in.

But DHCP is still there?

$ ps aux | grep dhc
root    ... dhclient3 -e IF_METRIC=100 -pf /var/run/dhclient.eth0.pid -lf /var/lib/dhcp/dhclient.eth0.leases -1 eth0

Is that normal? If not, how to restart interface in static IP while stop DHCP at the same time?

Thanks a lot.

Answer 1

1. You first have to shutdown the interface (in dhcp mode) sudo ifdown eth0

2. Then edit the config nano /etc/network/interfaces

   # The primary network interface
   auto eth0
   iface eth0 inet static
   netmask 255.255.0.0
   address 10.10.130.128
   gateway 10.10.1.1
   

3. Bring the interface back up sudo ifup eth0

Otherwise dhclient doesn't correctly shuts down,

Answer 2

I found for me, this was due to gnome's NetworkManager still running and thinking it was in charge of the device. In hindsight this should have been obvious as ps showed dhclient was being launched by NetworkManager.

Once I restarted my system the device went to "unmanaged" in NetworkManager and it stopped trying to configure it. Perhaps I could have achieved the same thing just by stopping/restarting NetworkManager, I'm not sure.

Answer 3

I had the same issue (Ubuntu 16.04), however this was a cloud instance and i could not ifdown the interface that easily.

short answer: i removed the file /etc/network/interface.d/50-cloud-init.cfg ifup was triggered by that specific file.

Long answer: I configured the interface using the /etc/network/interfaces with a static IP adress, but i still found in the daemon.log that dhclient was still requesting IP's from the DHCP and dhclient was started through systemd. Specifically systemd called the networking.service unit, which called ifup, which read both the interfaces file and the 50-cloud-init.cfg file. Resulting is some conflicts, but still a functional network.