What to do if ifconfig/ip link says "NO_CARRIER" in your Linux box even though the line is physically connected

There are times that make you into craziness. Your physical network connection is okay, the lamps on the interface card are flickering, and you see "NO_CARRIER" in your Linux box if you type ip link or ifconfig(deprecated). And guess what? In same machine, if you boot with Windows, you're actually connected to Internet!

Yes. That's what I experienced a few weeks ago. More precisely, the symptom was as follows:

1. Cold boot to Linux: NO_CARRIER
2. Cold boot to Windows and reboot to Linux: IT'S WORKING!(what?)

So, if I boot directly to Linux and I see NO_CARRIER message, but if I boot to Windows and reboot to Linux(warm boot) and my Linux can connect to the network as nothing happened.

Darn. Which curse did make my box as dull as possible like this? First I blamed my lovely bleeding-edge Arch Linux and built Gentoo stable, and later blamed dhcpcd and installed dhclient(in dhcp ebuild). I thought I got it with Gentoo+dhclient, but I was mistaken. Neither was the devil within.


I googled and in Arch Linux forum I found that there are several people with same issue, and it was NOT only atl1c module either. Some were using Marvel chipsets, some used the same Qualcomm Atheros, and so on. Their "collective intelligence" found out a solution, but it was of no effect to me(and some others in the forum), and I found yet the other cause for the issue.

So, here I leave things I found you can try(both googled ones and my own finding):

1. (My own finding)
   Disable "power up from PCI device" feature from BIOS. Yes. From BIOS. And it's done. Other "power up from....." settings(e.g. keyboard, mouse) were actually not related to the issue in any way(still I enable "power up from USB keyboard" feature).
2. (from https://bbs.archlinux.org/viewtopic.php?pid=994513#p994513)
   Send "on" message to the PCI system. e.g. echo on > /sys/bus/pci/devices/0000:00:XX.0/power/control

Simple, huh?

Hope this helps others with same symptom.