Nesrin

Find out what is bound before doing anything:

lspci -nnk | grep -A 3 -i ethernet

That prints the device, its numeric identifier, and the kernel module in use. Note the identifier — it is what you search with, and it is far more reliable than the marketing name on the box.

Then, in order of preference:

1. A newer kernel. Support for these controllers has improved steadily, and the single most effective fix is a kernel newer than the one your distribution shipped. Several distributions offer a newer kernel as a supported option, and this is far better than any manual driver because it keeps updating.

2. The vendor's out-of-tree driver, built and installed, with the in-kernel one blacklisted so it does not claim the device first. This works and it is a module you must rebuild on every kernel update unless you install it through the mechanism that does that automatically.

3. A cheap add-in card on a different chipset. Genuinely the right answer for some people — it costs less than an evening.

The reason it is the network port is specific and it is not bad luck: the 2.5 gigabit controllers from one popular vendor are a recent family, and the in-kernel driver situation for them has been messy for years.

What happens is that the kernel ships a driver for that vendor's long-established gigabit chips, and it also claims the newer 2.5 gigabit ones because they identify similarly. The result is one of three states depending on your kernel version:

• No interface at all — nothing claimed it.
• An interface that exists and never links — the wrong driver bound to it.
• An interface that works and drops under load, or negotiates at a lower speed.

All three are the same underlying situation. The other operating system works because the vendor ships a driver there directly.

So the question is which driver is bound, and the fix follows from the answer.

One practical addition: before any of this, know whether you have a backup you have actually restored from.

A move that goes wrong is only a scare if a restore is possible. The number of self-hosted setups where the backup exists and has never been tested is very high, and the moment you discover it is exactly this kind of maintenance.

Testing a restore of one album, one folder, one small thing, is an hour and it changes what every subsequent maintenance job feels like.