Ubuntu – How to disable ethernet check during boot

Blacklist the NIC driver

1. Create a blacklist file in /etc/modprobe.d/

Note that files in /etc/modprobe.d/ must have .conf suffix. Also naming modules in /etc/modprobe.d/blacklist.conf does not affect autoloading of modules by the kernel so you have to make your own file.

Example of a blacklist file: blacklist-ethernet.conf

blacklist driver_0     # eth0 by default

Note: here driver_0 is the name of your NIC driver. you can find the name of kernel driver for your LAN card by using the command lspci -v command in a terminal.
For Example my output was :

........
........ 
6:00.0 Ethernet controller: Broadcom Corporation NetLink BCM5906M Fast Ethernet PCI Express (rev 02)
    Subsystem: Lenovo Device 3861
    Flags: bus master, fast devsel, latency 0, IRQ 46
    Memory at b8000000 (64-bit, non-prefetchable) [size=64K]
    Expansion ROM at  [disabled]
    Capabilities: 
    Kernel driver in use: tg3
    Kernel modules: tg3
........
........

Here, I see the driver is tg3. so you need to write tg3(or your driver) in the place of driver_0.

2. Generate modules.dep and map files by running: depmod -ae

3. Recreate your initrd: update-initramfs -u

Plenty of info can be found here.

Here is how to fix this problem.

Edit file /usr/lib/NetworkManager/conf.d/10-globally-managed-devices.conf and change it's content from :

[keyfile]
unmanaged-devices=*,except:type:wifi,except:type:wwan

To :

[keyfile]
unmanaged-devices=*,except:type:ethernet,except:type:wifi,except:type:wwan

And then run :

sudo service network-manager restart

That's all.