[systemd-devel] when/where was support for assigning "ethX" names removed?

[Chris Friesen]

On 05/12/2016 11:36 AM, Lennart Poettering wrote:
> On Thu, 12.05.16 11:20, Chris Friesen (cbf123 at mail.usask.ca) wrote:
>
>> Hi,
>>
>> Could someone point me to the commit that removed support for assigning
>> "ethX" names based on MAC addresses?
>>
>> Alternately, can someone suggest a way to get equivalent behaviour (the
>> ability to set "ethX" names based on MAC address) using the current
>> infrastructure? (Preferably as of RHEL 7, so systemd 219 plus a bunch of
>> patches.)
>>
>> The back story is that we've got a lot of scripts/tools that currently
>> assume the "ethX" naming, and while we will eventually sort it out we really
>> don't want to do it right now.  The previous method of assigning "ethX"
>> names was working well for our use-case (though I realize it had issues more
>> generally).
>
> https://www.freedesktop.org/wiki/Software/systemd/PredictableNetworkInterfaceNames/
>
> See the end of that page.

I booted the kernel with "net.ifnames=0", which worked to turn off the 
location-based naming.

I then created a set of files, one per eth device that match based on MAC:

[root at compute-0 root]# cat /etc/systemd/network/10-eth
10-eth0.link  10-eth1.link  10-eth2.link  10-eth3.link


Here's an example of one of the files:

[root at compute-0 wrsroot]# cat /etc/systemd/network/10-eth0.link
[Match]
MACAddress=08:00:27:f1:36:11

[Link]
Name=eth0


When I booted up, however, the custom naming was not applied.  Eth0 was a 
different device:

[root at compute-0 wrsroot]# ip link

1: lo: <LOOPBACK,UP,LOWER_UP> mtu 65536 qdisc noqueue state UNKNOWN mode DEFAULT
     link/loopback 00:00:00:00:00:00 brd 00:00:00:00:00:00
2: eth0: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT qlen 1000
     link/ether 08:00:27:9f:b9:47 brd ff:ff:ff:ff:ff:ff
3: eth1: <BROADCAST,MULTICAST,UP,LOWER_UP> mtu 1500 qdisc pfifo_fast state UP 
mode DEFAULT qlen 1000
     link/ether 08:00:27:9d:14:c4 brd ff:ff:ff:ff:ff:ff
4: eth2: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT qlen 1000
     link/ether 08:00:27:f1:36:11 brd ff:ff:ff:ff:ff:ff
5: eth3: <BROADCAST,MULTICAST> mtu 1500 qdisc noop state DOWN mode DEFAULT qlen 1000
     link/ether 08:00:27:dd:42:ae brd ff:ff:ff:ff:ff:ff



If I use some other set of names (vethX, for example) then the renaming works fine.

I tried removing "net.ifnames=0" from the kernel boot args, and got devices 
named like "enp0s3" even though I had /etc/systemd/network/10-ethX.link files 
for each device.  This seems to contradict the information in 
https://www.freedesktop.org/software/systemd/man/systemd.link.html which says 
that the "Name=" should take effect if NamePolicy= is missing.

So I guess the question is, how do I rename a device to a name that already 
exists?  (Like supposing I want to swap the names of eth0 and eth1.)

Chris