Dec 16, 2013
3 min read
May 27, 2023 11:35 EEST

Installing QEmu

I use QEmu to have a emulated environment to test Xenomai applications without crashing the main system.

We need to enable sdl for qemu to have all display output available, edit /etc/portage/package.use:

app-emulation/qemu-softmmu sdl

To install QEmu on Gentoo we need at first gcc 3.x:

emerge =gcc-3.4.6*
gcc-config i686-pc-linux-gnu-3.4.6
source /etc/profile
emerge app-emulation/qemu
gcc-config i686-pc-linux-gnu-4.1.1
source /etc/profile

Prepare Linux for Qemu

Do as root:

echo 1024 > /proc/sys/dev/rtc/max-user-freq

Compile kernel with tun support.


Install everything for bridging:

emerge net-misc/bridge-utils
emerge sys-apps/usermode-utilities
modprobe tun
modprobe bridge

Note: If you get an error message about unresolved symbols, reboot easily the system then everything should work.

Configure for bridge device now in /etc/conf.d/net:

config_eth0=( "null" )
config_br0=( "" )
brctl_br0=( "setfd 0" "sethello 0" "stp off" )
routes_br0=( "default gw" )

Add the tun device to your startup config:

cd /etc/init.d
ln -s net.lo net.br0
rc-update add net.br0 default

/etc/init.d/net.eth0 stop
/etc/init.d/net.br0 start
ifconfig br0
ifconfig eth0

Configure Qemu to use a network interface edit /etc/qemu-ifup

# ____Address: (guest01)
# ____Netmask:
# ___Wildcard:
# ____Gateway:

if test $(sudo /sbin/ifconfig | grep -c $1) -gt 0; then
        sudo /sbin/brctl delif br0 $1
        sudo ifconfig $1 down

sudo /sbin/ifconfig $1 promisc up
sudo /sbin/brctl addif br0 $1
chmod +x /etc/qemu-ifup

Create a persistant tun interface:

tunctl -u root -t tap0

Booting OS in Qemu

We want to boot via network so we create first the needed structure in out tftp server.

  • Take the file pxelinux.0 from isolinux and copy it to the tftp root directory.
  • create a directory pxelinux.cfg
  • create the file pxelinux.cfg/default, see below for more details
  • copy kernel to zimage

The structure of the directory is:

|-- pxelinux.0
|-- pxelinux.cfg
|   |-- default
|   `-- zimage
`-- zimage

The file default has the following input:


LABEL qemu
  KERNEL zimage
  APPEND vga=0x314 install=nfs://

LABEL local

Now configure your dhcp server:

# settings for booting our qemu image
allow booting;
allow bootp;
filename "pxelinux.0";
mkdir qemu
cd !$
qemu-img create disk.img 4G
qemu -localtime -hda disk.img -boot d -m 256

You should see now some output. If you get the error message

Could not initialize SDL - exiting

Be sure that $DISPLAY is set and execute on the xserver xhost + to allow all hosts to connect to your xserver.

Now download pxe iso from http://rom-o-matic.net/ .

  • Choose as nic: ns8390:rtl8029 – [[0x10ec,0x8029]]
  • Select ISO bootable image for without legacy floppy emulation
  • Click Get ROM

Now we can boot via network with:

qemu -cdrom eb-5.4.2-ns8390.iso -boot d -net tap -net nic,macaddr=52:54:00:12:34:56

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