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I use the 'tap' net device with KVM to get my vm connect to the Internet. But I have to be root, or use 'sudo', which is inconvenient. I think I can put my user account into some group so I can access the net device without root privilege. I tried the netdev group, but does not work. My account is already in the kvm group.

What else should I do? Or is there any way to allow me using KVM freely without permission issue?

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2 Answers 2

up vote 3 down vote accepted

The group is whoever has read and write permissions to /dev/net/tun. The default setup varies from distribution to distribution. The ownership and permissions of devices is set by udev.

Create a file /etc/udev/rules.d/zzz_net_tun.rules containing

KERNEL=="tun", GROUP="netdev", MODE="0660", OPTIONS+="static_node=net/tun"

This will make the device accessible by all users in the netdev group. The setting takes effect when the device is created, so if it already exists, do chgrp netdev /dev/net/tun; chmod 660 /dev/net/tun.

(adapted from the Gentoo Wiki wiki)

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I tried the last two commands on my Ubuntu 15.04 box but user space applications still can't seem to access it: "qemu-system-arm: -net tap,ifname=tap0: could not configure /dev/net/tun (tap0): Operation not permitted". I verified that the group is set to netdev and permissions set to 0660. (And I'm in the netdev group.) – Nathan Osman Nov 16 at 2:30
@NathanOsman What's the output of groups and ls -l /dev/net/tun? Run strace -o qemu.strace qemu-system-arm net tap,ifname=tap0 … and look at the part of the trace where it tries to open /dev/net/tun. What's going on exactly? If you can't figure it out, ask a new question with all this information. – Gilles Nov 16 at 11:27
I finally decided to just ask a new question anyway: I'll still run strace and see if I can't get to the bottom of this. – Nathan Osman Nov 16 at 18:42

Make sure you are part of the KVM group also. The recommendantion is to make every virtualization things (network configuration, firmware access, qemu configuration) available for the kvm group.

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