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Linux Networking Devices

Udev naming

There a few network gotchas when adding a new network card or copying VMs. The issue starts when an existing the name of the network adapter changes (e.g., from eth0 to eth1) network adapter’s MAC address changes because a configuration script in linux associates the name of the network adapter with its MAC address. It can be disabled:

Disable udev persistent net generation

echo -n > /etc/udev/rules.d/70-persistent-net.rules
echo -n > /lib/udev/rules.d/75-persistent-net-generator.rules


# disable udev persistent net generation

echo -n > /etc/udev/rules.d/70-persistent-net.rules
echo -n > /etc/udev/rules.d/75-persistent-net-generator.rules


Systemd naming

With systemd, network devices are named differently(ie. enp0s0 or wlp2s0). Although this provides a more consistence naming convention with network adapters in linux, in some cases, The old style naming is sometimes needed for environments or scripts. To fix that, In grub:

Change:

title Gentoo Linux 4.4.1
root (hd0,0)
kernel /kernel-genkernel-x86_64-4.4.9-gentoo root=ZFS dozfs init=/usr/lib/systemd/systemd
initrd /initramfs-genkernel-x86_64-4.4.9-gentoo


To:

title Gentoo Linux 4.4.1
root (hd0,0)
kernel /kernel-genkernel-x86_64-4.4.9-gentoo root=ZFS dozfs init=/usr/lib/systemd/systemd net.ifnames=0
initrd /initramfs-genkernel-x86_64-4.4.9-gentoo


Magic SysReq

I have gotten into situations where the subsystems or subproccesses on a running system maybe not be performing as expected. If you ever need to reboot the host and its not connected to an pdu magic SysReq is the next best options.

You can activate it by:


echo 1 > /proc/sys/kernel/sysrq


If you need to reboot the host:

echo b > /proc/sysrq-trigger

Note: This will cause the kernel to send an instruction to the cpu to reset and it will not show down any processes cleanly and the same goes to the filesystem. USE WITH CAUTION!

To make it permanently turn on:

echo “kernel.sysrq = 1” » /etc/sysctl.conf


More infromation can be found: If you would like to learn more about magic SysRq you can read the sysrq.txt file in the kernel documentation. http://www.mjmwired.net/kernel/Documentation/sysrq.txt