wrapper script for starting Qemu VMs

start.sh

#!/usr/bin/env bash
# author: Florian Staudacher

###
# Usage:
#   ./start.sh
#     uses the configured base image, creates an overlay (if set) and starts
#     the VM. The overlay will be discarded at the end (you will have the
#     possibility to make a copy before it is deleted).
#
#   ./start.sh os_image.qcow2
#     uses the given image as base image, creates an overlay (if set) and starts
#     the VM. The overlay will be discarded (you may also keep it by copying it
#     somewhere when prompted).
###


################################################################################
##  CONFIG  ------------------------------------------------------------------##
################################################################################

# point this to a cdrom .img if you want to use one
#
# EXAMPLE:
#   VM_CDROM="my_cdrom.iso"
#
VM_CDROM=""

# point this to a local path in your filesystem to get it as SMB share in the
# guest OS. It should then be reachable under "\\10.0.2.4\qemu".
# for more info on qemu SLIRP networking, see:
#   http://wiki.qemu.org/Documentation/Networking#User_Networking_.28SLIRP.29
#
# NOTE: this requires an installed samba server on the host OS, also qemu
#       will have to be run as root, otherwise the samba server won't start.
#       There was a change in recent samba versions, so this will only work with
#       samba < 4.0 - in that case, you have to configure and start samba yourself.
#       see: http://bugs.debian.org/727756
#
# EXAMPLE:
#   VM_SMB_SHARE="/home/user/share"
#
VM_SMB_SHARE=""

# set the amount of memory used for the VM (in MB)
VM_MEMORY="768"

# set the name of the used VM (base) image
# this can also be a previously created overlay image
VM_IMAGE="root_image.qcow2"

# set a port forwarding from the host OS to the VM
# this only applies if "user networking" is used (which this script does)
#
# EXAMPLE:
#   VM_FWD_PORT="1234::80"
#
VM_FWD_PORT="10022::22"

# specify if you want to use a temporary overlay image to leave the original
# VM image untouched. The overlay image will be deleted after shutdown.
# To make permanent changes to the base image, don't use an overlay...
#
# EXAMPLE:
#   USE_OVERLAY=0
USE_OVERLAY=1

################################################################################

VM_USED_IMAGE="$VM_IMAGE"
REL_SCRIPT_PATH="`dirname \"$0\"`"
SCRIPT_PATH="`(cd \"$REL_SCRIPT_PATH\" && pwd )`"
TEMPNAME=`mktemp -u --suffix ".qcow2" "$SCRIPT_PATH/tmp.XXXXX"`

if [ -n "$1" ]; then
  VM_USED_IMAGE="$1"
fi

if [ "$USE_OVERLAY" -eq 1 ]; then
  qemu-img create -b "$VM_USED_IMAGE" -f qcow2 "$TEMPNAME"
  VM_USED_IMAGE="$TEMPNAME"
  printf "using temporary overlay image: %s\n" "$TEMPNAME"
fi

VM_CDROM_CMD=""
if [ -n "$VM_CDROM" ]; then
  VM_CDROM_CMD="-cdrom $VM_CDROM"
fi

VM_SMB_CMD=""
if [ -n "$VM_SMB_SHARE" ]; then
  VM_SMB_CMD=',smb='
  VM_SMB_CMD+="$VM_SMB_SHARE"
fi

VM_PORTFWD_CMD=""
if [ -n "$VM_FWD_PORT" ]; then
  VM_PORTFWD_CMD="-redir tcp:$VM_FWD_PORT"
fi

# check kernel word length
QEMU_CMD="qemu-system"
case `uname -m` in
  x86_64)
    QEMU_CMD="$QEMU_CMD-x86_64"
    ;;
  i686)
    QEMU_CMD="$QEMU_CMD-i386"
    ;;
  *)
    printf "unknown architecture\n"
    exit 1
  ;;
esac

# try to enable kvm, if available
VM_KVM_CMD=""
`lsmod | grep "kvm" >/dev/null 2>&1`
if [ $? -eq 0 ]; then
  VM_KVM_CMD="-enable-kvm"
fi

# start qemu
$QEMU_CMD -hda "$VM_USED_IMAGE" $VM_KVM_CMD -usb -usbdevice tablet -m "$VM_MEMORY" -rtc base=localtime -vga std -net nic,model=rtl8139 -net user$VM_SMB_CMD $VM_PORTFWD_CMD $VM_CDROM_CMD

# done ...

if [ "$USE_OVERLAY" -eq 1 ]; then
  printf "removing temporary overlay file\n"
  read -p "Press [Enter] to continue (copy the overlay somewhere to keep it) ..."
  rm "$TEMPNAME"
fi

printf "finished.\n"