Use of Predictable Network Interface Names with alternate kernels

Question

Almost constantly, I use kernels from the Ubuntu kernel PPA, or kernels I have compiled myself, using the Ubuntu kernel configuration.

The problem is when I am using the stock kernel it seems to default to using predictable network interface names (i.e. "p4p1"), but when I use any alternate kernel it seems to default to using the old method (i.e. "eth0").

While not really relevant to this question, I had a hard disk failure on my test computer and am doing a new install of Ubuntu Server 14.04.2.

I have not been able to determine what is the difference between the kernels. I suspect a kernel configuration parameter, but have been unable to identify which one.

My question: How can I make predictable network interface names work consistently across all kernels?

Additional notes: Somewhere I saw to disable predictable network interface names to add this to grub:

GRUB_CMDLINE_LINUX_DEFAULT="net.ifnames=0 biosdevname=0"

so, I thought the opposite might help:

GRUB_CMDLINE_LINUX_DEFAULT="net.ifnames=1 biosdevname=1"

but it made no difference. Actually, I can never get the non-stock kernel to use biosdevname, no matter the setting. And I can never get the stock kernel to generate a /etc/udev/rules.d/70-persistent-net.rules file (even though, that is not what I want), no matter the setting of net.ifnames. If I have net.ifnames=1, then at least the non-stock kernel doesn't generate an incorrect /etc/udev/rules.d/70-persistent-net.rules file.

Excerpts from /var/log/udev:
stock kernel:

KERNEL[9.216730] add      /devices/pci0000:00/0000:00:1c.4/0000:03:00.0/net/p4p1 (net)
ACTION=add
DEVPATH=/devices/pci0000:00/0000:00:1c.4/0000:03:00.0/net/p4p1
IFINDEX=2
INTERFACE=p4p1
SEQNUM=1945
SUBSYSTEM=net
...
UDEV  [9.241073] add      /devices/pci0000:00/0000:00:1c.4/0000:03:00.0/net/p4p1 (net)
ACTION=add
DEVPATH=/devices/pci0000:00/0000:00:1c.4/0000:03:00.0/net/p4p1
ID_BUS=pci
ID_MODEL_FROM_DATABASE=P8P67 and other motherboards
ID_MODEL_ID=0x8168
ID_NET_NAME_MAC=enxf46d04652d8e
ID_NET_NAME_PATH=enp3s0
ID_OUI_FROM_DATABASE=ASUSTek COMPUTER INC.
ID_PCI_CLASS_FROM_DATABASE=Network controller
ID_PCI_SUBCLASS_FROM_DATABASE=Ethernet controller
ID_VENDOR_FROM_DATABASE=Realtek Semiconductor Co., Ltd.
ID_VENDOR_ID=0x10ec
IFINDEX=2
INTERFACE=p4p1

From Ubuntu PPA kernel 4.1RC5:

KERNEL[10.772566] add      /devices/pci0000:00/0000:00:1c.4/0000:03:00.0/net/eth0 (net)
ACTION=add
DEVPATH=/devices/pci0000:00/0000:00:1c.4/0000:03:00.0/net/eth0
IFINDEX=2
INTERFACE=eth0
SEQNUM=1962
SUBSYSTEM=net
...
UDEV  [11.185866] add      /devices/pci0000:00/0000:00:1c.4/0000:03:00.0/net/eth0 (net)
ACTION=add
DEVPATH=/devices/pci0000:00/0000:00:1c.4/0000:03:00.0/net/eth0
ID_BUS=pci
ID_MODEL_FROM_DATABASE=P8P67 and other motherboards
ID_MODEL_ID=0x8168
ID_NET_NAME_MAC=enxf46d04652d8e
ID_NET_NAME_PATH=enp3s0
ID_OUI_FROM_DATABASE=ASUSTek COMPUTER INC.
ID_PCI_CLASS_FROM_DATABASE=Network controller
ID_PCI_SUBCLASS_FROM_DATABASE=Ethernet controller
ID_VENDOR_FROM_DATABASE=Realtek Semiconductor Co., Ltd.
ID_VENDOR_ID=0x10ec
IFINDEX=2
INTERFACE=eth0
SEQNUM=1962
SUBSYSTEM=net
USEC_INITIALIZED=3227

Note: I have temporarily moved past this issue by allowing a /etc/udev/rules.d/70-persistent-net.rules file to be created, and then editing it for proper device names. Ultimately, I would like to get rid of the file.

Solution 1

You need to distinguish between 3 things:

• Predictable interfaces names
• biosdevname
• 70-persistent.rules udev rule

You either choose to use one of these solution but you don't use 2 or 3 at the same time. (In fact, you can but one will take precedence and mask the other(s))

A good introduction to the current situation is the post on the ubuntu dev mailing list

Predictable interface names

Predictable interface names is a udevd thing since v197 generated in /lib/udev/rules.d/80-net-setup-link.rules

systemd use by default the new predictable interface name. However, unless upstream systemd, in Ubuntu, you have to opt-in by using net.ifnames=1

It does not matter the kernel version you are running. But you need to use the kernel command line to configure it by changing grub configuration /etc/default/grub, like:

GRUB_CMDLINE_LINUX_DEFAULT="net.ifnames=1"

and run

sudo update-grub

In 14.04 or 14.10, without systemd, it should be enough to remove 70-persitent-net.rules, as described below in the note.

Biosdevname

biosdevname is a dell attempt to solve a similar problem than predictable interface name in systemd. It is the default on ubuntu server. You can have it by installing the package biosdevname

sudo apt-get install biosdevname

Note

You can disable it by using kernel command line in grub config:

GRUB_CMDLINE_LINUX_DEFAULT="biosdevname=0"

and run

sudo update-grub

or simply uninstall the package.

sudo apt-get purge biosdevname
sudo update-initramfs -u

udev rules

This is the default on Ubuntu desktop. The udev rule /lib/udev/rules.d/75-persistent-net-generator.rules creates during the first boot a custom rules /etc/udev/rules.d/70-persistent-net.rules with MAC address of your interface to get persistent name for your interface.

Note

If you are already using udev rules, you need to remove /etc/udev/rules.d/70-persistent-net.rules and to avoid it being regenerated at each boot you need to run

sudo ln -s /dev/null /etc/udev/rules.d/75-persistent-net-generator.rules

After that, if you use systemd, then you need to opt-in for predictable interface name, as describe above.

Solution 2

1. In Ubuntu Server 16.04LTS all I did was run:

   ln -s /dev/null /etc/udev/rules.d/80-net-setup-link.rules
   

2. Then create the file using

   sudo vi /etc/systemd/network/10-internet.link
   

   and add the following

   [Match]
   Path=pci-0000:(your device mac address)
   
   [Link]
   Name=eth0 (or whatever you want to name it)
   

   :wq to save the file

3. then reboot and adjust your /etc/network/interfaces file.. then reboot again

Hope this helps someone

Comments

[Doug Smythies]

Thanks for your answer. My computer is server edition, not desktop edition. I'll submit an edit to your answer to deal with the difference (biosdevname was installed by default and therefore needs to be specifically disabled via grub). The error in my thinking was that I expected different interface names with net.ifnames=1 and biosdevname=0, as described in the link you gave, but I get the old eth0 and eth1. Anyway, it works for any kernel now (with no /etc/udev/rules.d/70-persistent-net.rules), after I edited /etc/network/interfaces to reflect the proper interface names.

[Jonathan Hartley]

I'm on ubuntu 15.10 desktop, and I don't think udev is the default any more. My network devices are named wlp4s0and enp0s31f6, and the files /etc/udev/rules.d/70-persistent-net.rules & /lib/udev/rules.d/75-persistent-net-generator.rules don't exist.

[200_success]

In Ubuntu 16.04 (specifically systemd 220-7), the 75-persistent-net-generator.rules file is deprecated in favour of net.ifnames.