Tools Index

Qemu

1. Host System

Prepare host system for virtual machines, this includes create new user, loading necessary modules and configure network. Load kvm module, in this example intel module is loaded but depends on host cpu;

        # modprobe -a kvm-intel tun virtio

Add users to kvm group;

        # usermod -a -G kvm c9admin
        # usermod -a -G kvm username

2. Disk images

Qemu supports multiple disk images types.

img: Raw disk image, allows dd to a physical device.
raw: Raw disk image, allows dd to a physical device.
qcow2: Qcow disk image file used by qemu.

Create hard disk image, there is different types, this describes how to create a qcow2 type;

        $ qemu-img create -f qcow2 crux-img.qcow2 20G

Qemu disk images can be treated as regular disks using qemu disk network block device server;

        $ sudo modprobe nbd
        $ sudo qemu-nbd -c /dev/nbd0 /crux-img.qcow2

Information about preparing partitions and storage administration. You can use image as a normal disk, example how to use parted to create a gpt system table;

        # parted --script $DEV \
            mklabel gpt \
            mkpart ESP fat32 1MiB 120MiB \
            mkpart primary ext4 120MiB 720MiB \
            mkpart primary ext4 720MiB 2720MiB \
            mkpart primary ext4 2720MiB 5000MiB \
            set 1 boot on

        # kpartx -a -s -l -u /dev/nbd0

Use /dev/mapper/$(name_of_device) to assign correct blocks;

        # mkfs.fat -F 32 $BLK_EFI
        # mkfs.ext4 $BLK_BOOT
        # mkfs.ext4 $BLK_ROOT
        # mkfs.ext4 $BLK_VAR

Mount partition;

        # mount $BLK_ROOT $CHROOT
        # mkdir -p $CHROOT/boot
        # mount $BLK_BOOT $CHROOT/boot
        # mkdir -p $CHROOT/boot/efi
        # mount $BLK_EFI $CHROOT/boot/efi
        # mkdir -p $CHROOT/var
        # mount $BLK_VAR $CHROOT/var

Before disconnecting image, clean dev mappings;

        $ sudo kpartx -d /dev/nbd0
        $ sudo qemu-nbd -d /dev/nbd0

2. Network

Network configuration;

slirp: Default virtual NAT'd network.
tun/tap: Good performance to create virtually any type of network topology.
vde: The VDE networking backend.

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

2.1. Routing

Create interface with correct permissions set for kvm group.

        # sysctl -w net.ipv4.ip_forward=1
        # iptables -A INPUT -i br0 -j ACCEPT
        # iptables -A FORWARD -i br0 -j ACCEPT
        # iptables -t nat -A POSTROUTING -s 10.0.0.0/24 -d 10.0.0.0/24 -j ACCEPT
        # iptables -t nat -A POSTROUTING -s 10.0.0.0/24 -j MASQUERADE

2.2. Public Bridge

Create bridge, create new tap and add it to bridge;

        DEV="br0"

        ADDR=10.0.0.254
        NET=10.0.0.0
        GW=192.168.1.254
        MASK=24

        # one tap for each cpu core
        NTAPS=$((`/usr/bin/nproc`))

        case $1 in
            start)
                /sbin/ip link add name ${DEV} type bridge
                /sbin/ip addr add ${ADDR}/${MASK} dev ${DEV} broadcast +
                /sbin/ip link set dev ${DEV} up
                /bin/sleep 0.2s

                for i in `/usr/bin/seq $NTAPS`
                do
                    TAP="tap$i"
                    echo "Setting up ${TAP} tap interface."
                    /sbin/ip tuntap add ${TAP} mode tap group kvm
                    /sbin/ip link set ${TAP} up
                    /bin/sleep 0.2s
                    /sbin/ip link set ${TAP} master ${DEV}
                done

                exit 0
                ;;
            stop)

                for i in `/usr/bin/seq $NTAPS`
                do
                    TAP="tap$i"
                    echo "Deleting ${TAP} tap interface."
                    /sbin/ip link del ${TAP}
                done

                /sbin/ip link set dev ${DEV} down
                /sbin/ip route flush dev ${DEV}
                /sbin/ip link del ${DEV}
                exit 0
                ;;
            restart)
                $0 stop
                $0 start
                ;;
            *)
                echo "Usage: $0 [start|stop|restart]"
                ;;
        esac

        # End of file

Guest System

See scripts/runvm/runvm.sh, as template. Example scripts;

runvm/profile/crux

        iso=iso/crux-3.2.iso
        image=img/crux-img.qcow2
        tap="tap1"

runvm/runvm.sh

        #!/bin/bash

        function rmac_addr (){
        printf '54:60:BE:EF:%02X:%02X\n' $((RANDOM%256)) $((RANDOM%256))
        }

        source profile/$1
        boot=$2

        mac=$(rmac_addr)

        qemu-system-x86_64 \
            -enable-kvm \
            -m 1024 \
            -boot ${boot} \
            -cdrom ${iso} \
            -hda ${image} \
            -vga std \
            -display sdl \
            -device e1000,netdev=t0,mac=${mac} \
            -netdev tap,id=t0,ifname=${tap},script=no,downscript=no \
            &

Set guests machines to run under the total resolution provided by host system configure grub on the guest with gfxmode;

        GRUB_GFXMODE=640x480
        GRUB_GFXPAYLOAD_LINUX=keep

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