Ubuntu 16.04 - system boot waits saying "Raise network interfaces"

It seems someone was paranoid about a client not getting it's DHCP in time.

Edit this file /etc/dhcp/dhclient.conf and set timeout to a reasonable value, like

timeout 15

The default value of 300 seconds is way too high. The suggested replacement value of 15 was tested and works fine.

So in your /etc/network/interfaces, change this:

# The primary network interface
auto eth0
iface eth0 inet dhcp

to this:

# The primary network interface
allow-hotplug eth0
iface eth0 inet dhcp

This will start interface eth0 when the kernel detects a hotplug event from the interface (i.e. when you plug a cable in), instead of starting it at boot.

As referenced in you can change the timeout value for raising the network interface (if running systemd):

Open a terminal window, and enter the command:

sudo nano /etc/systemd/system/network-online.target.wants/networking.service

Then change the line TimeoutStartSec=5min to a value that you choose. Save the file by pressing Ctrl+o and then Ctrl+x.

Finally, restart the daemon:

sudo systemctl daemon-reload