Eudev/en

For configurations not using systemd, eudev is Gentoo's device file manager for the Linux kernel. It manages device nodes in and handles all user space actions when adding or removing devices. It is a fork of systemd's udev with the goal of obtaining better compatibility with existing software such as OpenRC, Upstart, older kernels, various toolchains, and anything else required by (but not well supported through) udev. Configurations utilizing systemd should not use it.

USE flags
Some packages know the  USE flag for enabling  integration.

Emerge
To avoid registration in the world set, the oneshot option should be used.

RC service
The RC name is udev, not eudev. It needs to be registered in the sysinit runlevel.

From version 29 onward,   should also be added to the sysinit runlevel.

Migrating from udev to eudev
Migrating from udev 216 to eudev 1.10-r2 (March 2015) is straight forward:

In case the system uses multilib and, for example, has the  USE flag active against the older udev package, then don't forget to change it too:

Keep classic 'eth0' naming
Alternatively add  to the kernel command line, change the default policy or create a custom one.

An interesting resource related to the network naming is I don't like this, how do I disable this on the Freedesktop wiki.

Use new 'predictable' naming
The new network interface naming convention is not the same so interfaces will need to be re-linked. Use as a link target for whatever interface names need to be added. Be sure to replace   in the commands below with the Ethernet interface names present on the system. It is possible to discover which interfaces exist by running the command:

Create symbolic links for the existing interfaces in the and  directories:

Add the script(s) to the default runlevel to have the interface(s) start automatically:

Using udevadm
Start and see what happens:

Get device info using followed by the device path:

Get the device path using its name:

Test an event run using followed by the device path for which an event is to be tested:

To get a list of all commands:

udev 171-r10 to eudev 1.2-r1
See this post on the Gentoo forums.

Broken system switching from udev to eudev
See this post on the Gentoo forums.

External resources

 * Moving from udev (171-r10) to eudev (1.2-r1) on the Gentoo Forums