New Release: Systemd v249

Systemd v249 has been released. One substantial change that users need to be aware of is that this version will introduce a new naming scheme for network interfaces on RoCE Express adapters!

While previous versions would present a variety of interface names for RoCE Express adapters which were almost unpredictable, Systemd v249 changes the interface names to a new, simple scheme based on the user identifier (UID):

  eno<UID in decimal>

Use 1-9 for the UID of your interfaces to avoid the need to calculate the decimal value of the Linux interface name from the original UID value in hexadecimal.

However, this change may break network configurations that reference the interface name, depending upon the Linux distribution in use, as Linux distros often reference configurations using interface names. Therefore, adding a copy of the existing configuration using the new interface name might be a good idea! Since this change did not yet hit any of the major Linux distributions on Z, we will have to monitor what the actual experience is like as things develop further.

Note that usage of interface altnames might be a handy tool for backwards compatibility in existing scripts.

While most of the time, the exact interface name is of not much interest (otherwise, by now users would have revolted against the common PCI-based naming schemes that provide for easy to remember names like enP3p0s0np0...), they can be crucial to know for some of the distributions when e.g. installing to a new partition: Interface names might be used in PRM files for network-specific configuration at installation time.
With the previous scheme, guessing the interface name required a deep technical understanding of the interaction between systemd, the specific kernel level, and the IBM Z I/O configuration. With the new scheme, it becomes very easy - just beware to pay attention to the fact that the UID is displayed/handled in hex in most places. The interface name is the only spot to use decimal!

This change requires Linux kernel 5.13 or later.