Hacker's ramblings

I genuinely love my Arch Linux. It is a constant source of mischief. In a positive sense. There is always something changing making the entire setup explode. The joy I get, is when I need to get the pieces back together.

In the Wikipedia article of Arch Linux, there is a phrase:

... and expects the user to be willing to make some effort to understand the system's operation

The is precisely what I use my Arch Linux for. I want the practical experience and understanding on the system. And given it's rolling release approaches, it explodes plenty.

Back in 2014, Arch Linux impemented Consistent Network Device Naming. At that time the regular network interface names changed. For example my eth0 become ens3. My transition was not smooth. See my blog post about that.

Now it happened again! Whaat?

Symptoms:

• Failure to access the Linux-box via SSH
• Boot taking very long time
• Error message about service sys-subsystem-net-devices-ens3.device failing on startup

Failure:

Like previous time, the fix is about DHCP-client failing.

You vanilla query for DHCP-client status:

systemctl status dhcpcd@*

... resulted as nothingness. A more specific query for the failing interface:

systemctl status dhcpcd@ens3

... results:

* dhcpcd@ens3.service - dhcpcd on ens3
  Loaded: loaded (/usr/lib/systemd/system/dhcpcd@.service; enabled; vendor pre>
  Active: inactive (dead)

Yup. DHCP failure. Like previously, running ip addr show revealed the network interface name change:

2: enp0s3: mtu 1500 qdisc fq_codel state UP group default qlen 1000 link/ether 52:54:52:54:52:54 brd ff:ff:ff:ff:ff:ff

There is no more ens3, it is enp0s3 now. Ok.

Fix:

A simple disable for the non-existent interface's DHCP, and enable for the new one:

systemctl disable dhcpcd@ens3
systemctl enable dhcpcd@enp0s3

To test that, I rebooted the box. Yup. Working again!

Optional fix 2, for the syslog:

Debugging this wasn't as easy as I expected. dmesg had nothing on DHCP-clients and there was no kernel messages log at all! Whoa! Who ate that? I know, that default installation of Arch does not have syslog. I did have it running (I think) and now it was gone. Weird.

Documentation is at https://wiki.archlinux.org/index.php/Syslog-ng, but I simply did a:

pacman -S syslog-ng
systemctl enable syslog-ng@default
systemctl start syslog-ng@default

... and a 2nd reboot to confim, that the syslog existed and contained boot information. Done again!

What:

The subject of Consistent Network Device Naming is described in more detail here: https://access.redhat.com/documentation/en-us/red_hat_enterprise_linux/7/html/networking_guide/ch-consistent_network_device_naming

Apparently, there are five different approaches on how to actually implement the CNDN. And given the old ens-device,  which is according to PCI hotplug slot (enS for slot) index number (Scheme 2), the new naming scheme was chosen to be physical location (enP for physical) of the connector (Scheme 3).

The information of when/what/why the naming scheme change was made eludes me. I tried searching Arch discussion forums at https://bbs.archlinux.org/, but nothing there that I could find. But anyway, I got the pieces back together. Again!

Update 30th March 2018:
Yup. The interface naming rolled back. Now ens3 is the interface used again. Darnnation this naming flapping!