QEMU Emulator User Documentation

Table of Contents

1. Introduction

1.1 Features

QEMU is a FAST! processor emulator using dynamic translation to achieve good emulation speed.

QEMU has two operating modes:

QEMU can run without an host kernel driver and yet gives acceptable performance.

For system emulation, the following hardware targets are supported:

For user emulation, x86, PowerPC, ARM, 32-bit MIPS, Sparc32/64, ColdFire(m68k), CRISv32 and MicroBlaze CPUs are supported.

2. Installation

If you want to compile QEMU yourself, see section 6. Compilation from the sources.

2.1 Linux

If a precompiled package is available for your distribution - you just have to install it. Otherwise, see section 6. Compilation from the sources.

2.2 Windows

Download the experimental binary installer at http://www.free.oszoo.org/@/download.html.

2.3 Mac OS X

Download the experimental binary installer at http://www.free.oszoo.org/@/download.html.

3. QEMU PC System emulator

3.1 Introduction

The QEMU PC System emulator simulates the following peripherals:

SMP is supported with up to 255 CPUs.

Note that adlib, gus and cs4231a are only available when QEMU was configured with --audio-card-list option containing the name(s) of required card(s).

QEMU uses the PC BIOS from the Bochs project and the Plex86/Bochs LGPL VGA BIOS.

QEMU uses YM3812 emulation by Tatsuyuki Satoh.

QEMU uses GUS emulation(GUSEMU32 http://www.deinmeister.de/gusemu/) by Tibor "TS" Schütz.

Not that, by default, GUS shares IRQ(7) with parallel ports and so qemu must be told to not have parallel ports to have working GUS 

qemu dos.img -soundhw gus -parallel none

Alternatively: 

qemu dos.img -device gus,irq=5

Or some other unclaimed IRQ.

CS4231A is the chip used in Windows Sound System and GUSMAX products

3.2 Quick Start

Download and uncompress the linux image (`linux.img') and type: 

qemu linux.img

Linux should boot and give you a prompt.

3.3 Invocation

usage: qemu [options] [disk_image]

disk_image is a raw hard disk image for IDE hard disk 0. Some targets do not need a disk image.

Standard options:

@option{-h}
Display help and exit
@option{-version}
Display version information and exit
@option{-M machine}
Select the emulated machine (-M ? for list)
@option{-cpu model}
Select CPU model (-cpu ? for list and additional feature selection)
@option{-smp n[,cores=cores][,threads=threads][,sockets=sockets][,maxcpus=maxcpus]}
Simulate an SMP system with n CPUs. On the PC target, up to 255 CPUs are supported. On Sparc32 target, Linux limits the number of usable CPUs to 4. For the PC target, the number of cores per socket, the number of threads per cores and the total number of sockets can be specified. Missing values will be computed. If any on the three values is given, the total number of CPUs n can be omitted. maxcpus specifies the maximum number of hotpluggable CPUs.
@option{-numa opts}
Simulate a multi node NUMA system. If mem and cpus are omitted, resources are split equally.
@option{-fda file}
@option{-fdb file}
Use file as floppy disk 0/1 image (see section 3.6 Disk Images). You can use the host floppy by using `/dev/fd0' as filename (see section 3.6.6 Using host drives).
@option{-hda file}
@option{-hdb file}
@option{-hdc file}
@option{-hdd file}
Use file as hard disk 0, 1, 2 or 3 image (see section 3.6 Disk Images).
@option{-cdrom file}
Use file as CD-ROM image (you cannot use @option{-hdc} and @option{-cdrom} at the same time). You can use the host CD-ROM by using `/dev/cdrom' as filename (see section 3.6.6 Using host drives).
@option{-drive option[,option[,option[,...]]]}
Define a new drive. Valid options are:
@option{file=file}
This option defines which disk image (see section 3.6 Disk Images) to use with this drive. If the filename contains comma, you must double it (for instance, "file=my,,file" to use file "my,file").
@option{if=interface}
This option defines on which type on interface the drive is connected. Available types are: ide, scsi, sd, mtd, floppy, pflash, virtio.
@option{bus=bus,unit=unit}
These options define where is connected the drive by defining the bus number and the unit id.
@option{index=index}
This option defines where is connected the drive by using an index in the list of available connectors of a given interface type.
@option{media=media}
This option defines the type of the media: disk or cdrom.
@option{cyls=c,heads=h,secs=s[,trans=t]}
These options have the same definition as they have in @option{-hdachs}.
@option{snapshot=snapshot}
snapshot is "on" or "off" and allows to enable snapshot for given drive (see @option{-snapshot}).
@option{cache=cache}
cache is "none", "writeback", or "writethrough" and controls how the host cache is used to access block data.
@option{aio=aio}
aio is "threads", or "native" and selects between pthread based disk I/O and native Linux AIO.
@option{format=format}
Specify which disk format will be used rather than detecting the format. Can be used to specifiy format=raw to avoid interpreting an untrusted format header.
@option{serial=serial}
This option specifies the serial number to assign to the device.
@option{addr=addr}
Specify the controller's PCI address (if=virtio only).
By default, writethrough caching is used for all block device. This means that the host page cache will be used to read and write data but write notification will be sent to the guest only when the data has been reported as written by the storage subsystem. Writeback caching will report data writes as completed as soon as the data is present in the host page cache. This is safe as long as you trust your host. If your host crashes or loses power, then the guest may experience data corruption. When using the @option{-snapshot} option, writeback caching is used by default. The host page cache can be avoided entirely with @option{cache=none}. This will attempt to do disk IO directly to the guests memory. QEMU may still perform an internal copy of the data. Some block drivers perform badly with @option{cache=writethrough}, most notably, qcow2. If performance is more important than correctness, @option{cache=writeback} should be used with qcow2. Instead of @option{-cdrom} you can use: 
qemu -drive file=file,index=2,media=cdrom
Instead of @option{-hda}, @option{-hdb}, @option{-hdc}, @option{-hdd}, you can use: 
qemu -drive file=file,index=0,media=disk
qemu -drive file=file,index=1,media=disk
qemu -drive file=file,index=2,media=disk
qemu -drive file=file,index=3,media=disk
You can connect a CDROM to the slave of ide0: 
qemu -drive file=file,if=ide,index=1,media=cdrom
If you don't specify the "file=" argument, you define an empty drive: 
qemu -drive if=ide,index=1,media=cdrom
You can connect a SCSI disk with unit ID 6 on the bus #0: 
qemu -drive file=file,if=scsi,bus=0,unit=6
Instead of @option{-fda}, @option{-fdb}, you can use: 
qemu -drive file=file,index=0,if=floppy
qemu -drive file=file,index=1,if=floppy
By default, interface is "ide" and index is automatically incremented: 
qemu -drive file=a -drive file=b"
is interpreted like: 
qemu -hda a -hdb b
@option{-mtdblock file}
Use file as on-board Flash memory image.
@option{-sd file}
Use file as SecureDigital card image.
@option{-pflash file}
Use file as a parallel flash image.
@option{-boot [order=drives][,once=drives][,menu=on|off]}
Specify boot order drives as a string of drive letters. Valid drive letters depend on the target achitecture. The x86 PC uses: a, b (floppy 1 and 2), c (first hard disk), d (first CD-ROM), n-p (Etherboot from network adapter 1-4), hard disk boot is the default. To apply a particular boot order only on the first startup, specify it via @option{once}. Interactive boot menus/prompts can be enabled via @option{menu=on} as far as firmware/BIOS supports them. The default is non-interactive boot. 
# try to boot from network first, then from hard disk
qemu -boot order=nc
# boot from CD-ROM first, switch back to default order after reboot
qemu -boot once=d
Note: The legacy format '-boot drives' is still supported but its use is discouraged as it may be removed from future versions.
@option{-snapshot}
Write to temporary files instead of disk image files. In this case, the raw disk image you use is not written back. You can however force the write back by pressing C-a s (see section 3.6 Disk Images).
@option{-m megs}
Set virtual RAM size to megs megabytes. Default is 128 MiB. Optionally, a suffix of "M" or "G" can be used to signify a value in megabytes or gigabytes respectively.
@option{-k language}
Use keyboard layout language (for example fr for French). This option is only needed where it is not easy to get raw PC keycodes (e.g. on Macs, with some X11 servers or with a VNC display). You don't normally need to use it on PC/Linux or PC/Windows hosts. The available layouts are: 
ar  de-ch  es  fo     fr-ca  hu  ja  mk     no  pt-br  sv
da  en-gb  et  fr     fr-ch  is  lt  nl     pl  ru     th
de  en-us  fi  fr-be  hr     it  lv  nl-be  pt  sl     tr
The default is en-us.
@option{-audio-help}
Will show the audio subsystem help: list of drivers, tunable parameters.
@option{-soundhw card1[,card2,...] or -soundhw all}
Enable audio and selected sound hardware. Use ? to print all available sound hardware. 
qemu -soundhw sb16,adlib disk.img
qemu -soundhw es1370 disk.img
qemu -soundhw ac97 disk.img
qemu -soundhw all disk.img
qemu -soundhw ?
Note that Linux's i810_audio OSS kernel (for AC97) module might require manually specifying clocking. 
modprobe i810_audio clocking=48000

USB options:

@option{-usb}
Enable the USB driver (will be the default soon)
@option{-usbdevice devname}
Add the USB device devname. See section 3.9.1 Connecting USB devices.
@option{mouse}
Virtual Mouse. This will override the PS/2 mouse emulation when activated.
@option{tablet}
Pointer device that uses absolute coordinates (like a touchscreen). This means qemu is able to report the mouse position without having to grab the mouse. Also overrides the PS/2 mouse emulation when activated.
@option{disk:[format=format]:file}
Mass storage device based on file. The optional format argument will be used rather than detecting the format. Can be used to specifiy format=raw to avoid interpreting an untrusted format header.
@option{host:bus.addr}
Pass through the host device identified by bus.addr (Linux only).
@option{host:vendor_id:product_id}
Pass through the host device identified by vendor_id:product_id (Linux only).
@option{serial:[vendorid=vendor_id][,productid=product_id]:dev}
Serial converter to host character device dev, see -serial for the available devices.
@option{braille}
Braille device. This will use BrlAPI to display the braille output on a real or fake device.
@option{net:options}
Network adapter that supports CDC ethernet and RNDIS protocols.
@option{-name name}
Sets the name of the guest. This name will be displayed in the SDL window caption. The name will also be used for the VNC server. Also optionally set the top visible process name in Linux.
@option{-uuid uuid}
Set system UUID.

Display options:

@option{-nographic}
Normally, QEMU uses SDL to display the VGA output. With this option, you can totally disable graphical output so that QEMU is a simple command line application. The emulated serial port is redirected on the console. Therefore, you can still use QEMU to debug a Linux kernel with a serial console.
@option{-curses}
Normally, QEMU uses SDL to display the VGA output. With this option, QEMU can display the VGA output when in text mode using a curses/ncurses interface. Nothing is displayed in graphical mode.
@option{-no-frame}
Do not use decorations for SDL windows and start them using the whole available screen space. This makes the using QEMU in a dedicated desktop workspace more convenient.
@option{-alt-grab}
Use Ctrl-Alt-Shift to grab mouse (instead of Ctrl-Alt).
@option{-ctrl-grab}
Use Right-Ctrl to grab mouse (instead of Ctrl-Alt).
@option{-no-quit}
Disable SDL window close capability.
@option{-sdl}
Enable SDL.
@option{-portrait}
Rotate graphical output 90 deg left (only PXA LCD).
@option{-vga type}
Select type of VGA card to emulate. Valid values for type are
@option{cirrus}
Cirrus Logic GD5446 Video card. All Windows versions starting from Windows 95 should recognize and use this graphic card. For optimal performances, use 16 bit color depth in the guest and the host OS. (This one is the default)
@option{std}
Standard VGA card with Bochs VBE extensions. If your guest OS supports the VESA 2.0 VBE extensions (e.g. Windows XP) and if you want to use high resolution modes (>= 1280x1024x16) then you should use this option.
@option{vmware}
VMWare SVGA-II compatible adapter. Use it if you have sufficiently recent XFree86/XOrg server or Windows guest with a driver for this card.
@option{none}
Disable VGA card.
@option{-full-screen}
Start in full screen.
@option{-vnc display[,option[,option[,...]]]}
Normally, QEMU uses SDL to display the VGA output. With this option, you can have QEMU listen on VNC display display and redirect the VGA display over the VNC session. It is very useful to enable the usb tablet device when using this option (option @option{-usbdevice tablet}). When using the VNC display, you must use the @option{-k} parameter to set the keyboard layout if you are not using en-us. Valid syntax for the display is
@option{host:d}
TCP connections will only be allowed from host on display d. By convention the TCP port is 5900+d. Optionally, host can be omitted in which case the server will accept connections from any host.
@option{unix:path}
Connections will be allowed over UNIX domain sockets where path is the location of a unix socket to listen for connections on.
@option{none}
VNC is initialized but not started. The monitor change command can be used to later start the VNC server.
Following the display value there may be one or more option flags separated by commas. Valid options are
@option{reverse}
Connect to a listening VNC client via a "reverse" connection. The client is specified by the display. For reverse network connections (host:d,reverse), the d argument is a TCP port number, not a display number.
@option{password}
Require that password based authentication is used for client connections. The password must be set separately using the change command in the section 3.5 QEMU Monitor
@option{tls}
Require that client use TLS when communicating with the VNC server. This uses anonymous TLS credentials so is susceptible to a man-in-the-middle attack. It is recommended that this option be combined with either the @option{x509} or @option{x509verify} options.
@option{x509=/path/to/certificate/dir}
Valid if @option{tls} is specified. Require that x509 credentials are used for negotiating the TLS session. The server will send its x509 certificate to the client. It is recommended that a password be set on the VNC server to provide authentication of the client when this is used. The path following this option specifies where the x509 certificates are to be loaded from. See the section 3.10 VNC security section for details on generating certificates.
@option{x509verify=/path/to/certificate/dir}
Valid if @option{tls} is specified. Require that x509 credentials are used for negotiating the TLS session. The server will send its x509 certificate to the client, and request that the client send its own x509 certificate. The server will validate the client's certificate against the CA certificate, and reject clients when validation fails. If the certificate authority is trusted, this is a sufficient authentication mechanism. You may still wish to set a password on the VNC server as a second authentication layer. The path following this option specifies where the x509 certificates are to be loaded from. See the section 3.10 VNC security section for details on generating certificates.
@option{sasl}
Require that the client use SASL to authenticate with the VNC server. The exact choice of authentication method used is controlled from the system / user's SASL configuration file for the 'qemu' service. This is typically found in /etc/sasl2/qemu.conf. If running QEMU as an unprivileged user, an environment variable SASL_CONF_PATH can be used to make it search alternate locations for the service config. While some SASL auth methods can also provide data encryption (eg GSSAPI), it is recommended that SASL always be combined with the 'tls' and 'x509' settings to enable use of SSL and server certificates. This ensures a data encryption preventing compromise of authentication credentials. See the section 3.10 VNC security section for details on using SASL authentication.
@option{acl}
Turn on access control lists for checking of the x509 client certificate and SASL party. For x509 certs, the ACL check is made against the certificate's distinguished name. This is something that looks like C=GB,O=ACME,L=Boston,CN=bob. For SASL party, the ACL check is made against the username, which depending on the SASL plugin, may include a realm component, eg bob or bob@EXAMPLE.COM. When the @option{acl} flag is set, the initial access list will be empty, with a deny policy. Thus no one will be allowed to use the VNC server until the ACLs have been loaded. This can be achieved using the acl monitor command.

i386 target only:

@option{-win2k-hack}
Use it when installing Windows 2000 to avoid a disk full bug. After Windows 2000 is installed, you no longer need this option (this option slows down the IDE transfers).
@option{-no-fd-bootchk}
Disable boot signature checking for floppy disks in Bochs BIOS. It may be needed to boot from old floppy disks.
@option{-no-acpi}
Disable ACPI (Advanced Configuration and Power Interface) support. Use it if your guest OS complains about ACPI problems (PC target machine only).
@option{-no-hpet}
Disable HPET support.
@option{-balloon none}
Disable balloon device.
@option{-balloon virtio[,addr=addr]}
Enable virtio balloon device (default), optionally with PCI address addr.
@option{-acpitable [sig=str][,rev=n][,oem_id=str][,oem_table_id=str][,oem_rev=n] [,asl_compiler_id=str][,asl_compiler_rev=n][,data=file1[:file2]...]}
Add ACPI table with specified header fields and context from specified files.
@option{-smbios file=binary}
Load SMBIOS entry from binary file.
@option{-smbios type=0[,vendor=str][,version=str][,date=str][,release=%d.%d]}
Specify SMBIOS type 0 fields
@option{-smbios type=1[,manufacturer=str][,product=str][,version=str][,serial=str][,uuid=uuid][,sku=str][,family=str]}
Specify SMBIOS type 1 fields

Network options:

@option{-net nic[,vlan=n][,macaddr=mac][,model=type][,name=name][,addr=addr][,vectors=v]}
Create a new Network Interface Card and connect it to VLAN n (n = 0 is the default). The NIC is an e1000 by default on the PC target. Optionally, the MAC address can be changed to mac, the device address set to addr (PCI cards only), and a name can be assigned for use in monitor commands. Optionally, for PCI cards, you can specify the number v of MSI-X vectors that the card should have; this option currently only affects virtio cards; set v = 0 to disable MSI-X. If no @option{-net} option is specified, a single NIC is created. Qemu can emulate several different models of network card. Valid values for type are virtio, i82551, i82557b, i82559er, ne2k_pci, ne2k_isa, pcnet, rtl8139, e1000, smc91c111, lance and mcf_fec. Not all devices are supported on all targets. Use -net nic,model=? for a list of available devices for your target.
@option{-net user[,option][,option][,...]}
Use the user mode network stack which requires no administrator privilege to run. Valid options are:
@option{vlan=n}
Connect user mode stack to VLAN n (n = 0 is the default).
@option{name=name}
Assign symbolic name for use in monitor commands.
@option{net=addr[/mask]}
Set IP network address the guest will see. Optionally specify the netmask, either in the form a.b.c.d or as number of valid top-most bits. Default is 10.0.2.0/8.
@option{host=addr}
Specify the guest-visible address of the host. Default is the 2nd IP in the guest network, i.e. x.x.x.2.
@option{restrict=y|yes|n|no}
If this options is enabled, the guest will be isolated, i.e. it will not be able to contact the host and no guest IP packets will be routed over the host to the outside. This option does not affect explicitly set forwarding rule.
@option{hostname=name}
Specifies the client hostname reported by the builtin DHCP server.
@option{dhcpstart=addr}
Specify the first of the 16 IPs the built-in DHCP server can assign. Default is the 16th to 31st IP in the guest network, i.e. x.x.x.16 to x.x.x.31.
@option{dns=addr}
Specify the guest-visible address of the virtual nameserver. The address must be different from the host address. Default is the 3rd IP in the guest network, i.e. x.x.x.3.
@option{tftp=dir}
When using the user mode network stack, activate a built-in TFTP server. The files in dir will be exposed as the root of a TFTP server. The TFTP client on the guest must be configured in binary mode (use the command bin of the Unix TFTP client).
@option{bootfile=file}
When using the user mode network stack, broadcast file as the BOOTP filename. In conjunction with @option{tftp}, this can be used to network boot a guest from a local directory. Example (using pxelinux): 
qemu -hda linux.img -boot n -net user,tftp=/path/to/tftp/files,bootfile=/pxelinux.0
@option{smb=dir[,smbserver=addr]}
When using the user mode network stack, activate a built-in SMB server so that Windows OSes can access to the host files in `dir' transparently. The IP address of the SMB server can be set to addr. By default the 4th IP in the guest network is used, i.e. x.x.x.4. In the guest Windows OS, the line: 
10.0.2.4 smbserver
must be added in the file `C:\WINDOWS\LMHOSTS' (for windows 9x/Me) or `C:\WINNT\SYSTEM32\DRIVERS\ETC\LMHOSTS' (Windows NT/2000). Then `dir' can be accessed in `\\smbserver\qemu'. Note that a SAMBA server must be installed on the host OS in `/usr/sbin/smbd'. QEMU was tested successfully with smbd versions from Red Hat 9, Fedora Core 3 and OpenSUSE 11.x.
@option{hostfwd=[tcp|udp]:[hostaddr]:hostport-[guestaddr]:guestport}
Redirect incoming TCP or UDP connections to the host port hostport to the guest IP address guestaddr on guest port guestport. If guestaddr is not specified, its value is x.x.x.15 (default first address given by the built-in DHCP server). By specifying hostaddr, the rule can be bound to a specific host interface. If no connection type is set, TCP is used. This option can be given multiple times. For example, to redirect host X11 connection from screen 1 to guest screen 0, use the following: 
# on the host
qemu -net user,hostfwd=tcp:127.0.0.1:6001-:6000 [...]
# this host xterm should open in the guest X11 server
xterm -display :1
To redirect telnet connections from host port 5555 to telnet port on the guest, use the following: 
# on the host
qemu -net user,hostfwd=tcp:5555::23 [...]
telnet localhost 5555
Then when you use on the host telnet localhost 5555, you connect to the guest telnet server.
@option{guestfwd=[tcp]:server:port-dev}
Forward guest TCP connections to the IP address server on port port to the character device dev. This option can be given multiple times.
Note: Legacy stand-alone options -tftp, -bootp, -smb and -redir are still processed and applied to -net user. Mixing them with the new configuration syntax gives undefined results. Their use for new applications is discouraged as they will be removed from future versions.
@option{-net tap[,vlan=n][,name=name][,fd=h][,ifname=name][,script=file][,downscript=dfile]}
Connect the host TAP network interface name to VLAN n, use the network script file to configure it and the network script dfile to deconfigure it. If name is not provided, the OS automatically provides one. @option{fd}=h can be used to specify the handle of an already opened host TAP interface. The default network configure script is `/etc/qemu-ifup' and the default network deconfigure script is `/etc/qemu-ifdown'. Use @option{script=no} or @option{downscript=no} to disable script execution. Example: 
qemu linux.img -net nic -net tap
More complicated example (two NICs, each one connected to a TAP device) 
qemu linux.img -net nic,vlan=0 -net tap,vlan=0,ifname=tap0 \
-net nic,vlan=1 -net tap,vlan=1,ifname=tap1
@option{-net socket[,vlan=n][,name=name][,fd=h][,listen=[host]:port][,connect=host:port]}
Connect the VLAN n to a remote VLAN in another QEMU virtual machine using a TCP socket connection. If @option{listen} is specified, QEMU waits for incoming connections on port (host is optional). @option{connect} is used to connect to another QEMU instance using the @option{listen} option. @option{fd}=h specifies an already opened TCP socket. Example: 
# launch a first QEMU instance
qemu linux.img -net nic,macaddr=52:54:00:12:34:56 \
-net socket,listen=:1234
# connect the VLAN 0 of this instance to the VLAN 0
# of the first instance
qemu linux.img -net nic,macaddr=52:54:00:12:34:57 \
-net socket,connect=127.0.0.1:1234
@option{-net socket[,vlan=n][,name=name][,fd=h][,mcast=maddr:port]}
Create a VLAN n shared with another QEMU virtual machines using a UDP multicast socket, effectively making a bus for every QEMU with same multicast address maddr and port. NOTES:
  1. Several QEMU can be running on different hosts and share same bus (assuming correct multicast setup for these hosts).
  2. mcast support is compatible with User Mode Linux (argument @option{ethN=mcast}), see http://user-mode-linux.sf.net.
  3. Use @option{fd=h} to specify an already opened UDP multicast socket.
Example: 
# launch one QEMU instance
qemu linux.img -net nic,macaddr=52:54:00:12:34:56 \
-net socket,mcast=230.0.0.1:1234
# launch another QEMU instance on same "bus"
qemu linux.img -net nic,macaddr=52:54:00:12:34:57 \
-net socket,mcast=230.0.0.1:1234
# launch yet another QEMU instance on same "bus"
qemu linux.img -net nic,macaddr=52:54:00:12:34:58 \
-net socket,mcast=230.0.0.1:1234
Example (User Mode Linux compat.): 
# launch QEMU instance (note mcast address selected
# is UML's default)
qemu linux.img -net nic,macaddr=52:54:00:12:34:56 \
-net socket,mcast=239.192.168.1:1102
# launch UML
/path/to/linux ubd0=/path/to/root_fs eth0=mcast
@option{-net vde[,vlan=n][,name=name][,sock=socketpath][,port=n][,group=groupname][,mode=octalmode]}
Connect VLAN n to PORT n of a vde switch running on host and listening for incoming connections on socketpath. Use GROUP groupname and MODE octalmode to change default ownership and permissions for communication port. This option is available only if QEMU has been compiled with vde support enabled. Example: 
# launch vde switch
vde_switch -F -sock /tmp/myswitch
# launch QEMU instance
qemu linux.img -net nic -net vde,sock=/tmp/myswitch
@option{-net dump[,vlan=n][,file=file][,len=len]}
Dump network traffic on VLAN n to file file (`qemu-vlan0.pcap' by default). At most len bytes (64k by default) per packet are stored. The file format is libpcap, so it can be analyzed with tools such as tcpdump or Wireshark.
@option{-net none}
Indicate that no network devices should be configured. It is used to override the default configuration (@option{-net nic -net user}) which is activated if no @option{-net} options are provided.

Character device options:

The general form of a character device option is:

@option{-chardev backend ,id=id [,options]}
Backend is one of: @option{null}, @option{socket}, @option{udp}, @option{msmouse}, @option{vc}, @option{file}, @option{pipe}, @option{console}, @option{serial}, @option{pty}, @option{stdio}, @option{braille}, @option{tty}, @option{parport}. The specific backend will determine the applicable options. All devices must have an id, which can be any string up to 127 characters long. It is used to uniquely identify this device in other command line directives. Options to each backend are described below.
@option{-chardev null ,id=id}
A void device. This device will not emit any data, and will drop any data it receives. The null backend does not take any options.
@option{-chardev socket ,id=id [TCP options or unix options] [,server] [,nowait] [,telnet]}
Create a two-way stream socket, which can be either a TCP or a unix socket. A unix socket will be created if @option{path} is specified. Behaviour is undefined if TCP options are specified for a unix socket. @option{server} specifies that the socket shall be a listening socket. @option{nowait} specifies that QEMU should not block waiting for a client to connect to a listening socket. @option{telnet} specifies that traffic on the socket should interpret telnet escape sequences. TCP and unix socket options are given below:
@option{TCP options: port=host [,host=host] [,to=to] [,ipv4] [,ipv6] [,nodelay]}
@option{host} for a listening socket specifies the local address to be bound. For a connecting socket species the remote host to connect to. @option{host} is optional for listening sockets. If not specified it defaults to 0.0.0.0. @option{port} for a listening socket specifies the local port to be bound. For a connecting socket specifies the port on the remote host to connect to. @option{port} can be given as either a port number or a service name. @option{port} is required. @option{to} is only relevant to listening sockets. If it is specified, and @option{port} cannot be bound, QEMU will attempt to bind to subsequent ports up to and including @option{to} until it succeeds. @option{to} must be specified as a port number. @option{ipv4} and @option{ipv6} specify that either IPv4 or IPv6 must be used. If neither is specified the socket may use either protocol. @option{nodelay} disables the Nagle algorithm.
@option{unix options: path=path}
@option{path} specifies the local path of the unix socket. @option{path} is required.
@option{-chardev udp ,id=id [,host=host] ,port=port [,localaddr=localaddr] [,localport=localport] [,ipv4] [,ipv6]}
Sends all traffic from the guest to a remote host over UDP. @option{host} specifies the remote host to connect to. If not specified it defaults to localhost. @option{port} specifies the port on the remote host to connect to. @option{port} is required. @option{localaddr} specifies the local address to bind to. If not specified it defaults to 0.0.0.0. @option{localport} specifies the local port to bind to. If not specified any available local port will be used. @option{ipv4} and @option{ipv6} specify that either IPv4 or IPv6 must be used. If neither is specified the device may use either protocol.
@option{-chardev msmouse ,id=id}
Forward QEMU's emulated msmouse events to the guest. @option{msmouse} does not take any options.
@option{-chardev vc ,id=id [[,width=width] [,height=height]] [[,cols=cols] [,rows=rows]]}
Connect to a QEMU text console. @option{vc} may optionally be given a specific size. @option{width} and @option{height} specify the width and height respectively of the console, in pixels. @option{cols} and @option{rows} specify that the console be sized to fit a text console with the given dimensions.
@option{-chardev file ,id=id ,path=path}
Log all traffic received from the guest to a file. @option{path} specifies the path of the file to be opened. This file will be created if it does not already exist, and overwritten if it does. @option{path} is required.
@option{-chardev pipe ,id=id ,path=path}
Create a two-way connection to the guest. The behaviour differs slightly between Windows hosts and other hosts: On Windows, a single duplex pipe will be created at `\\.pipe\@option{path'}. On other hosts, 2 pipes will be created called `@option{path'.in} and `@option{path'.out}. Data written to @file{@option{path}.in} will be received by the guest. Data written by the guest can be read from `@option{path'.out}. QEMU will not create these fifos, and requires them to be present. @option{path} forms part of the pipe path as described above. @option{path} is required.
@option{-chardev console ,id=id}
Send traffic from the guest to QEMU's standard output. @option{console} does not take any options. @option{console} is only available on Windows hosts.
@option{-chardev serial ,id=id ,path=@option{path}}
Send traffic from the guest to a serial device on the host. @option{serial} is only available on Windows hosts. @option{path} specifies the name of the serial device to open.
@option{-chardev pty ,id=id}
Create a new pseudo-terminal on the host and connect to it. @option{pty} does not take any options. @option{pty} is not available on Windows hosts.
@option{-chardev stdio ,id=id}
Connect to standard input and standard output of the qemu process. @option{stdio} does not take any options. @option{stdio} is not available on Windows hosts.
@option{-chardev braille ,id=id}
Connect to a local BrlAPI server. @option{braille} does not take any options.
@option{-chardev tty ,id=id ,path=path}
Connect to a local tty device. @option{tty} is only available on Linux, Sun, FreeBSD, NetBSD, OpenBSD and DragonFlyBSD hosts. @option{path} specifies the path to the tty. @option{path} is required.
@option{-chardev parport ,id=id ,path=path}
@option{parport} is only available on Linux, FreeBSD and DragonFlyBSD hosts. Connect to a local parallel port. @option{path} specifies the path to the parallel port device. @option{path} is required.

Bluetooth(R) options:

@option{-bt hci[...]}
Defines the function of the corresponding Bluetooth HCI. -bt options are matched with the HCIs present in the chosen machine type. For example when emulating a machine with only one HCI built into it, only the first -bt hci[...] option is valid and defines the HCI's logic. The Transport Layer is decided by the machine type. Currently the machines n800 and n810 have one HCI and all other machines have none. @anchor{bt-hcis} The following three types are recognized:
@option{-bt hci,null}
(default) The corresponding Bluetooth HCI assumes no internal logic and will not respond to any HCI commands or emit events.
@option{-bt hci,host[:id]}
(bluez only) The corresponding HCI passes commands / events to / from the physical HCI identified by the name id (default: hci0) on the computer running QEMU. Only available on bluez capable systems like Linux.
@option{-bt hci[,vlan=n]}
Add a virtual, standard HCI that will participate in the Bluetooth scatternet n (default 0). Similarly to @option{-net} VLANs, devices inside a bluetooth network n can only communicate with other devices in the same network (scatternet).
@option{-bt vhci[,vlan=n]}
(Linux-host only) Create a HCI in scatternet n (default 0) attached to the host bluetooth stack instead of to the emulated target. This allows the host and target machines to participate in a common scatternet and communicate. Requires the Linux vhci driver installed. Can be used as following: 
qemu [...OPTIONS...] -bt hci,vlan=5 -bt vhci,vlan=5
@option{-bt device:dev[,vlan=n]}
Emulate a bluetooth device dev and place it in network n (default 0). QEMU can only emulate one type of bluetooth devices currently:
@option{keyboard}
Virtual wireless keyboard implementing the HIDP bluetooth profile.

Linux/Multiboot boot specific:

When using these options, you can use a given Linux or Multiboot kernel without installing it in the disk image. It can be useful for easier testing of various kernels.

@option{-kernel bzImage}
Use bzImage as kernel image. The kernel can be either a Linux kernel or in multiboot format.
@option{-append cmdline}
Use cmdline as kernel command line
@option{-initrd file}
Use file as initial ram disk.
@option{-initrd "file1 arg=foo,file2"}
This syntax is only available with multiboot. Use file1 and file2 as modules and pass arg=foo as parameter to the first module.

Debug/Expert options:

@option{-serial dev}
Redirect the virtual serial port to host character device dev. The default device is vc in graphical mode and stdio in non graphical mode. This option can be used several times to simulate up to 4 serial ports. Use -serial none to disable all serial ports. Available character devices are:
@option{vc[:WxH]}
Virtual console. Optionally, a width and height can be given in pixel with 
vc:800x600
It is also possible to specify width or height in characters: 
vc:80Cx24C
@option{pty}
[Linux only] Pseudo TTY (a new PTY is automatically allocated)
@option{none}
No device is allocated.
@option{null}
void device
@option{/dev/XXX}
[Linux only] Use host tty, e.g. `/dev/ttyS0'. The host serial port parameters are set according to the emulated ones.
@option{/dev/parportN}
[Linux only, parallel port only] Use host parallel port N. Currently SPP and EPP parallel port features can be used.
@option{file:filename}
Write output to filename. No character can be read.
@option{stdio}
[Unix only] standard input/output
@option{pipe:filename}
name pipe filename
@option{COMn}
[Windows only] Use host serial port n
@option{udp:[remote_host]:remote_port[@[src_ip]:src_port]}
This implements UDP Net Console. When remote_host or src_ip are not specified they default to 0.0.0.0. When not using a specified src_port a random port is automatically chosen. If you just want a simple readonly console you can use netcat or nc, by starting qemu with: -serial udp::4555 and nc as: nc -u -l -p 4555. Any time qemu writes something to that port it will appear in the netconsole session. If you plan to send characters back via netconsole or you want to stop and start qemu a lot of times, you should have qemu use the same source port each time by using something like -serial udp::4555@:4556 to qemu. Another approach is to use a patched version of netcat which can listen to a TCP port and send and receive characters via udp. If you have a patched version of netcat which activates telnet remote echo and single char transfer, then you can use the following options to step up a netcat redirector to allow telnet on port 5555 to access the qemu port.
Qemu Options:
-serial udp::4555@:4556
netcat options:
-u -P 4555 -L 0.0.0.0:4556 -t -p 5555 -I -T
telnet options:
localhost 5555
@option{tcp:[host]:port[,server][,nowait][,nodelay]}
The TCP Net Console has two modes of operation. It can send the serial I/O to a location or wait for a connection from a location. By default the TCP Net Console is sent to host at the port. If you use the server option QEMU will wait for a client socket application to connect to the port before continuing, unless the nowait option was specified. The nodelay option disables the Nagle buffering algorithm. If host is omitted, 0.0.0.0 is assumed. Only one TCP connection at a time is accepted. You can use telnet to connect to the corresponding character device.
Example to send tcp console to 192.168.0.2 port 4444
-serial tcp:192.168.0.2:4444
Example to listen and wait on port 4444 for connection
-serial tcp::4444,server
Example to not wait and listen on ip 192.168.0.100 port 4444
-serial tcp:192.168.0.100:4444,server,nowait
@option{telnet:host:port[,server][,nowait][,nodelay]}
The telnet protocol is used instead of raw tcp sockets. The options work the same as if you had specified -serial tcp. The difference is that the port acts like a telnet server or client using telnet option negotiation. This will also allow you to send the MAGIC_SYSRQ sequence if you use a telnet that supports sending the break sequence. Typically in unix telnet you do it with Control-] and then type "send break" followed by pressing the enter key.
@option{unix:path[,server][,nowait]}
A unix domain socket is used instead of a tcp socket. The option works the same as if you had specified -serial tcp except the unix domain socket path is used for connections.
@option{mon:dev_string}
This is a special option to allow the monitor to be multiplexed onto another serial port. The monitor is accessed with key sequence of Control-a and then pressing c. See monitor access section 3.4 Keys in the -nographic section for more keys. dev_string should be any one of the serial devices specified above. An example to multiplex the monitor onto a telnet server listening on port 4444 would be:
-serial mon:telnet::4444,server,nowait
@option{braille}
Braille device. This will use BrlAPI to display the braille output on a real or fake device.
@option{msmouse}
Three button serial mouse. Configure the guest to use Microsoft protocol.
@option{-parallel dev}
Redirect the virtual parallel port to host device dev (same devices as the serial port). On Linux hosts, `/dev/parportN' can be used to use hardware devices connected on the corresponding host parallel port. This option can be used several times to simulate up to 3 parallel ports. Use -parallel none to disable all parallel ports.
@option{-monitor dev}
Redirect the monitor to host device dev (same devices as the serial port). The default device is vc in graphical mode and stdio in non graphical mode.
@option{-mon chardev=[name][,mode=readline|control][,default]}
Setup monitor on chardev name.
@option{-pidfile file}
Store the QEMU process PID in file. It is useful if you launch QEMU from a script.
@option{-singlestep}
Run the emulation in single step mode.
@option{-S}
Do not start CPU at startup (you must type 'c' in the monitor).
@option{-gdb dev}
Wait for gdb connection on device dev (see section 3.11 GDB usage). Typical connections will likely be TCP-based, but also UDP, pseudo TTY, or even stdio are reasonable use case. The latter is allowing to start qemu from within gdb and establish the connection via a pipe: 
(gdb) target remote | exec qemu -gdb stdio ...
@option{-s}
Shorthand for -gdb tcp::1234, i.e. open a gdbserver on TCP port 1234 (see section 3.11 GDB usage).
@option{-d}
Output log in /tmp/qemu.log
@option{-hdachs c,h,s,[,t]}
Force hard disk 0 physical geometry (1 <= c <= 16383, 1 <= h <= 16, 1 <= s <= 63) and optionally force the BIOS translation mode (t=none, lba or auto). Usually QEMU can guess all those parameters. This option is useful for old MS-DOS disk images.
@option{-L path}
Set the directory for the BIOS, VGA BIOS and keymaps.
@option{-bios file}
Set the filename for the BIOS.
@option{-enable-kvm}
Enable KVM full virtualization support. This option is only available if KVM support is enabled when compiling.
@option{-no-reboot}
Exit instead of rebooting.
@option{-no-shutdown}
Don't exit QEMU on guest shutdown, but instead only stop the emulation. This allows for instance switching to monitor to commit changes to the disk image.
@option{-loadvm file}
Start right away with a saved state (loadvm in monitor)
@option{-daemonize}
Daemonize the QEMU process after initialization. QEMU will not detach from standard IO until it is ready to receive connections on any of its devices. This option is a useful way for external programs to launch QEMU without having to cope with initialization race conditions.
@option{-option-rom file}
Load the contents of file as an option ROM. This option is useful to load things like EtherBoot.
@option{-clock method}
Force the use of the given methods for timer alarm. To see what timers are available use -clock ?.
@option{-rtc [base=utc|localtime|date][,clock=host|vm][,driftfix=none|slew]}
Specify @option{base} as utc or localtime to let the RTC start at the current UTC or local time, respectively. localtime is required for correct date in MS-DOS or Windows. To start at a specific point in time, provide date in the format 2006-06-17T16:01:21 or 2006-06-17. The default base is UTC. By default the RTC is driven by the host system time. This allows to use the RTC as accurate reference clock inside the guest, specifically if the host time is smoothly following an accurate external reference clock, e.g. via NTP. If you want to isolate the guest time from the host, even prevent it from progressing during suspension, you can set @option{clock} to vm instead. Enable @option{driftfix} (i386 targets only) if you experience time drift problems, specifically with Windows' ACPI HAL. This option will try to figure out how many timer interrupts were not processed by the Windows guest and will re-inject them.
@option{-icount [N|auto]}
Enable virtual instruction counter. The virtual cpu will execute one instruction every 2^N ns of virtual time. If auto is specified then the virtual cpu speed will be automatically adjusted to keep virtual time within a few seconds of real time. Note that while this option can give deterministic behavior, it does not provide cycle accurate emulation. Modern CPUs contain superscalar out of order cores with complex cache hierarchies. The number of instructions executed often has little or no correlation with actual performance.
@option{-watchdog model}
Create a virtual hardware watchdog device. Once enabled (by a guest action), the watchdog must be periodically polled by an agent inside the guest or else the guest will be restarted. The model is the model of hardware watchdog to emulate. Choices for model are: ib700 (iBASE 700) which is a very simple ISA watchdog with a single timer, or i6300esb (Intel 6300ESB I/O controller hub) which is a much more featureful PCI-based dual-timer watchdog. Choose a model for which your guest has drivers. Use -watchdog ? to list available hardware models. Only one watchdog can be enabled for a guest.
@option{-watchdog-action action}
The action controls what QEMU will do when the watchdog timer expires. The default is reset (forcefully reset the guest). Other possible actions are: shutdown (attempt to gracefully shutdown the guest), poweroff (forcefully poweroff the guest), pause (pause the guest), debug (print a debug message and continue), or none (do nothing). Note that the shutdown action requires that the guest responds to ACPI signals, which it may not be able to do in the sort of situations where the watchdog would have expired, and thus -watchdog-action shutdown is not recommended for production use. Examples:
-watchdog i6300esb -watchdog-action pause
-watchdog ib700
@option{-echr numeric_ascii_value}
Change the escape character used for switching to the monitor when using monitor and serial sharing. The default is 0x01 when using the -nographic option. 0x01 is equal to pressing Control-a. You can select a different character from the ascii control keys where 1 through 26 map to Control-a through Control-z. For instance you could use the either of the following to change the escape character to Control-t.
-echr 0x14
-echr 20
@option{-virtioconsole c}
Set virtio console.
@option{-chroot dir}
Immediately before starting guest execution, chroot to the specified directory. Especially useful in combination with -runas.
@option{-runas user}
Immediately before starting guest execution, drop root privileges, switching to the specified user.

3.4 Keys

During the graphical emulation, you can use the following keys:

Ctrl-Alt-f
Toggle full screen
Ctrl-Alt-u
Restore the screen's un-scaled dimensions
Ctrl-Alt-n
Switch to virtual console 'n'. Standard console mappings are:
1
Target system display
2
Monitor
3
Serial port
Ctrl-Alt
Toggle mouse and keyboard grab.

In the virtual consoles, you can use Ctrl-Up, Ctrl-Down, Ctrl-PageUp and Ctrl-PageDown to move in the back log.

During emulation, if you are using the @option{-nographic} option, use Ctrl-a h to get terminal commands:

Ctrl-a h
Ctrl-a ?
Print this help
Ctrl-a x
Exit emulator
Ctrl-a s
Save disk data back to file (if -snapshot)
Ctrl-a t
Toggle console timestamps
Ctrl-a b
Send break (magic sysrq in Linux)
Ctrl-a c
Switch between console and monitor
Ctrl-a Ctrl-a
Send Ctrl-a

3.5 QEMU Monitor

The QEMU monitor is used to give complex commands to the QEMU emulator. You can use it to:

3.5.1 Commands

The following commands are available:

@option{help or ? [cmd]}
Show the help for all commands or just for command cmd.
@option{commit}
Commit changes to the disk images (if -snapshot is used) or backing files.
@option{info subcommand}
Show various information about the system state.
@option{info version}
show the version of QEMU
@option{info network}
show the various VLANs and the associated devices
@option{info chardev}
show the character devices
@option{info block}
show the block devices
@option{info block}
show block device statistics
@option{info registers}
show the cpu registers
@option{info cpus}
show infos for each CPU
@option{info history}
show the command line history
@option{info irq}
show the interrupts statistics (if available)
@option{info pic}
show i8259 (PIC) state
@option{info pci}
show emulated PCI device info
@option{info tlb}
show virtual to physical memory mappings (i386 only)
@option{info mem}
show the active virtual memory mappings (i386 only)
@option{info hpet}
show state of HPET (i386 only)
@option{info kvm}
show KVM information
@option{info usb}
show USB devices plugged on the virtual USB hub
@option{info usbhost}
show all USB host devices
@option{info profile}
show profiling information
@option{info capture}
show information about active capturing
@option{info snapshots}
show list of VM snapshots
@option{info status}
show the current VM status (running|paused)
@option{info pcmcia}
show guest PCMCIA status
@option{info mice}
show which guest mouse is receiving events
@option{info vnc}
show the vnc server status
@option{info name}
show the current VM name
@option{info uuid}
show the current VM UUID
@option{info cpustats}
show CPU statistics
@option{info usernet}
show user network stack connection states
@option{info migrate}
show migration status
@option{info balloon}
show balloon information
@option{info qtree}
show device tree
@option{q or quit}
Quit the emulator.
@option{eject [-f] device}
Eject a removable medium (use -f to force it).
@option{change device setting}
Change the configuration of a device.
@option{change diskdevice filename [format]}
Change the medium for a removable disk device to point to filename. eg 
(qemu) change ide1-cd0 /path/to/some.iso
format is optional.
@option{change vnc display,options}
Change the configuration of the VNC server. The valid syntax for display and options are described at section 3.3 Invocation. eg 
(qemu) change vnc localhost:1
@option{change vnc password [password]}
Change the password associated with the VNC server. If the new password is not supplied, the monitor will prompt for it to be entered. VNC passwords are only significant up to 8 letters. eg 
(qemu) change vnc password
Password: ********
@option{screendump filename}
Save screen into PPM image filename.
@option{logfile filename}
Output logs to filename.
@option{log item1[,...]}
Activate logging of the specified items to `/tmp/qemu.log'.
@option{savevm [tag|id]}
Create a snapshot of the whole virtual machine. If tag is provided, it is used as human readable identifier. If there is already a snapshot with the same tag or ID, it is replaced. More info at section 3.6.3 VM snapshots.
@option{loadvm tag|id}
Set the whole virtual machine to the snapshot identified by the tag tag or the unique snapshot ID id.
@option{delvm tag|id}
Delete the snapshot identified by tag or id.
@option{singlestep [off]}
Run the emulation in single step mode. If called with option off, the emulation returns to normal mode.
@option{stop}
Stop emulation.
@option{c or cont}
Resume emulation.
@option{gdbserver [port]}
Start gdbserver session (default port=1234)
@option{x/fmt addr}
Virtual memory dump starting at addr.
@option{xp /fmt addr}
Physical memory dump starting at addr. fmt is a format which tells the command how to format the data. Its syntax is: @option{/{count}{format}{size}}
count
is the number of items to be dumped.
format
can be x (hex), d (signed decimal), u (unsigned decimal), o (octal), c (char) or i (asm instruction).
size
can be b (8 bits), h (16 bits), w (32 bits) or g (64 bits). On x86, h or w can be specified with the i format to respectively select 16 or 32 bit code instruction size.
Examples:
@option{p or print/fmt expr}
Print expression value. Only the format part of fmt is used. Read I/O port. Write to I/O port.
@option{sendkey keys}
Send keys to the emulator. keys could be the name of the key or # followed by the raw value in either decimal or hexadecimal format. Use - to press several keys simultaneously. Example: 
sendkey ctrl-alt-f1
This command is useful to send keys that your graphical user interface intercepts at low level, such as ctrl-alt-f1 in X Window.
@option{system_reset}
Reset the system.
@option{system_powerdown}
Power down the system (if supported).
@option{sum addr size}
Compute the checksum of a memory region.
@option{usb_add devname}
Add the USB device devname. For details of available devices see section 3.9.1 Connecting USB devices
@option{usb_del devname}
Remove the USB device devname from the QEMU virtual USB hub. devname has the syntax bus.addr. Use the monitor command info usb to see the devices you can remove.
@option{device_add config}
Add device.
@option{device_del id}
Remove device id. Set the default CPU.
@option{mouse_move dx dy [dz]}
Move the active mouse to the specified coordinates dx dy with optional scroll axis dz.
@option{mouse_button val}
Change the active mouse button state val (1=L, 2=M, 4=R).
@option{mouse_set index}
Set which mouse device receives events at given index, index can be obtained with 
info mice
@option{wavcapture filename [frequency [bits [channels]]]}
Capture audio into filename. Using sample rate frequency bits per sample bits and number of channels channels. Defaults:
@option{stopcapture index}
Stop capture with a given index, index can be obtained with 
info capture
@option{memsave addr size file}
save to disk virtual memory dump starting at addr of size size.
@option{pmemsave addr size file}
save to disk physical memory dump starting at addr of size size.
@option{boot_set bootdevicelist}
Define new values for the boot device list. Those values will override the values specified on the command line through the -boot option. The values that can be specified here depend on the machine type, but are the same that can be specified in the -boot command line option.
@option{nmi cpu}
Inject an NMI on the given CPU (x86 only).
@option{migrate [-d] [-b] [-i] uri}
Migrate to uri (using -d to not wait for completion). -b for migration with full copy of disk -i for migration with incremental copy of disk (base image is shared)
@option{migrate_cancel}
Cancel the current VM migration.
@option{migrate_set_speed value}
Set maximum speed to value (in bytes) for migrations.
@option{migrate_set_downtime second}
Set maximum tolerated downtime (in seconds) for migration.
@option{drive_add}
Add drive to PCI storage controller.
@option{pci_add}
Hot-add PCI device.
@option{pci_del}
Hot remove PCI device.
@option{host_net_add}
Add host VLAN client.
@option{host_net_remove}
Remove host VLAN client.
@option{host_net_redir}
Redirect TCP or UDP connections from host to guest (requires -net user).
@option{balloon value}
Request VM to change its memory allocation to value (in MB).
@option{set_link name [up|down]}
Set link name up or down.
@option{watchdog_action}
Change watchdog action.
@option{acl_show aclname}
List all the matching rules in the access control list, and the default policy. There are currently two named access control lists, vnc.x509dname and vnc.username matching on the x509 client certificate distinguished name, and SASL username respectively.
@option{acl_policy aclname allow|deny}
Set the default access control list policy, used in the event that none of the explicit rules match. The default policy at startup is always deny.
@option{acl_allow aclname match allow|deny [index]}
Add a match rule to the access control list, allowing or denying access. The match will normally be an exact username or x509 distinguished name, but can optionally include wildcard globs. eg *@EXAMPLE.COM to allow all users in the EXAMPLE.COM kerberos realm. The match will normally be appended to the end of the ACL, but can be inserted earlier in the list if the optional index parameter is supplied.
@option{acl_remove aclname match}
Remove the specified match rule from the access control list.
@option{acl_remove aclname match}
Remove all matches from the access control list, and set the default policy back to deny.
@option{mce cpu bank status mcgstatus addr misc}
Inject an MCE on the given CPU (x86 only).
@option{getfd fdname}
If a file descriptor is passed alongside this command using the SCM_RIGHTS mechanism on unix sockets, it is stored using the name fdname for later use by other monitor commands.
@option{closefd fdname}
Close the file descriptor previously assigned to fdname using the getfd command. This is only needed if the file descriptor was never used by another monitor command.
@option{block_passwd device password}
Set the encrypted device device password to password

3.5.2 Integer expressions

The monitor understands integers expressions for every integer argument. You can use register names to get the value of specifics CPU registers by prefixing them with $.

3.6 Disk Images

Since version 0.6.1, QEMU supports many disk image formats, including growable disk images (their size increase as non empty sectors are written), compressed and encrypted disk images. Version 0.8.3 added the new qcow2 disk image format which is essential to support VM snapshots.

3.6.1 Quick start for disk image creation

You can create a disk image with the command: 

qemu-img create myimage.img mysize

where myimage.img is the disk image filename and mysize is its size in kilobytes. You can add an M suffix to give the size in megabytes and a G suffix for gigabytes.

See section 3.6.4 qemu-img Invocation for more information.

3.6.2 Snapshot mode

If you use the option @option{-snapshot}, all disk images are considered as read only. When sectors in written, they are written in a temporary file created in `/tmp'. You can however force the write back to the raw disk images by using the commit monitor command (or C-a s in the serial console).

3.6.3 VM snapshots

VM snapshots are snapshots of the complete virtual machine including CPU state, RAM, device state and the content of all the writable disks. In order to use VM snapshots, you must have at least one non removable and writable block device using the qcow2 disk image format. Normally this device is the first virtual hard drive.

Use the monitor command savevm to create a new VM snapshot or replace an existing one. A human readable name can be assigned to each snapshot in addition to its numerical ID.

Use loadvm to restore a VM snapshot and delvm to remove a VM snapshot. info snapshots lists the available snapshots with their associated information: 

(qemu) info snapshots
Snapshot devices: hda
Snapshot list (from hda):
ID        TAG                 VM SIZE                DATE       VM CLOCK
1         start                   41M 2006-08-06 12:38:02   00:00:14.954
2                                 40M 2006-08-06 12:43:29   00:00:18.633
3         msys                    40M 2006-08-06 12:44:04   00:00:23.514

A VM snapshot is made of a VM state info (its size is shown in info snapshots) and a snapshot of every writable disk image. The VM state info is stored in the first qcow2 non removable and writable block device. The disk image snapshots are stored in every disk image. The size of a snapshot in a disk image is difficult to evaluate and is not shown by info snapshots because the associated disk sectors are shared among all the snapshots to save disk space (otherwise each snapshot would need a full copy of all the disk images).

When using the (unrelated) -snapshot option (section 3.6.2 Snapshot mode), you can always make VM snapshots, but they are deleted as soon as you exit QEMU.

VM snapshots currently have the following known limitations:

3.6.4 qemu-img Invocation

usage: qemu-img command [command options]

The following commands are supported:

@option{check [-f fmt] filename}
@option{create [-f fmt] [-o options] filename [size]}
@option{commit [-f fmt] filename}
@option{convert [-c] [-f fmt] [-O output_fmt] [-o options] filename [filename2 [...]] output_filename}
@option{info [-f fmt] filename}
@option{snapshot [-l | -a snapshot | -c snapshot | -d snapshot] filename}

Command parameters:

filename
is a disk image filename
fmt
is the disk image format. It is guessed automatically in most cases. See below for a description of the supported disk formats.
size
is the disk image size in bytes. Optional suffixes k or K (kilobyte, 1024) M (megabyte, 1024k) and G (gigabyte, 1024M) and T (terabyte, 1024G) are supported. b is ignored.
output_filename
is the destination disk image filename
output_fmt
is the destination format
options
is a comma separated list of format specific options in a name=value format. Use -o ? for an overview of the options supported by the used format or see the format descriptions below for details.
-c
indicates that target image must be compressed (qcow format only)
-h
with or without a command shows help and lists the supported formats

Parameters to snapshot subcommand:

@option{snapshot}
is the name of the snapshot to create, apply or delete
@option{-a}
applies a snapshot (revert disk to saved state)
@option{-c}
creates a snapshot
@option{-d}
deletes a snapshot
@option{-l}
lists all snapshots in the given image

Command description:

@option{create [-f fmt] [-o options] filename [size]}
Create the new disk image filename of size size and format fmt. Depending on the file format, you can add one or more options that enable additional features of this format. If the option backing_file is specified, then the image will record only the differences from backing_file. No size needs to be specified in this case. backing_file will never be modified unless you use the commit monitor command (or qemu-img commit). The size can also be specified using the size option with -o, it doesn't need to be specified separately in this case.
@option{commit [-f fmt] filename}
Commit the changes recorded in filename in its base image.
@option{convert [-c] [-f fmt] [-O output_fmt] [-o options] filename [filename2 [...]] output_filename}
Convert the disk image filename to disk image output_filename using format output_fmt. It can be optionally compressed (-c option) or use any format specific options like encryption (-o option). Only the formats qcow and qcow2 support compression. The compression is read-only. It means that if a compressed sector is rewritten, then it is rewritten as uncompressed data. Image conversion is also useful to get smaller image when using a growable format such as qcow or cow: the empty sectors are detected and suppressed from the destination image. You can use the backing_file option to force the output image to be created as a copy on write image of the specified base image; the backing_file should have the same content as the input's base image, however the path, image format, etc may differ.
@option{info [-f fmt] filename}
Give information about the disk image filename. Use it in particular to know the size reserved on disk which can be different from the displayed size. If VM snapshots are stored in the disk image, they are displayed too.
@option{snapshot [-l | -a snapshot | -c snapshot | -d snapshot ] filename}
List, apply, create or delete snapshots in image filename.

Supported image file formats:

@option{raw}
Raw disk image format (default). This format has the advantage of being simple and easily exportable to all other emulators. If your file system supports holes (for example in ext2 or ext3 on Linux or NTFS on Windows), then only the written sectors will reserve space. Use qemu-img info to know the real size used by the image or ls -ls on Unix/Linux.
@option{host_device}
Host device format. This format should be used instead of raw when converting to block devices or other devices where "holes" are not supported.
@option{qcow2}
QEMU image format, the most versatile format. Use it to have smaller images (useful if your filesystem does not supports holes, for example on Windows), optional AES encryption, zlib based compression and support of multiple VM snapshots. Supported options:
backing_file
File name of a base image (see @option{create} subcommand)
backing_fmt
Image format of the base image
encryption
If this option is set to on, the image is encrypted. Encryption uses the AES format which is very secure (128 bit keys). Use a long password (16 characters) to get maximum protection.
cluster_size
Changes the qcow2 cluster size (must be between 512 and 2M). Smaller cluster sizes can improve the image file size whereas larger cluster sizes generally provide better performance.
preallocation
Preallocation mode (allowed values: off, metadata). An image with preallocated metadata is initially larger but can improve performance when the image needs to grow.
@option{qcow}
Old QEMU image format. Left for compatibility. Supported options:
backing_file
File name of a base image (see @option{create} subcommand)
encryption
If this option is set to on, the image is encrypted.
@option{cow}
User Mode Linux Copy On Write image format. Used to be the only growable image format in QEMU. It is supported only for compatibility with previous versions. It does not work on win32.
@option{vdi}
VirtualBox 1.1 compatible image format.
@option{vmdk}
VMware 3 and 4 compatible image format. Supported options:
backing_fmt
Image format of the base image
compat6
Create a VMDK version 6 image (instead of version 4)
@option{vpc}
VirtualPC compatible image format (VHD).
@option{cloop}
Linux Compressed Loop image, useful only to reuse directly compressed CD-ROM images present for example in the Knoppix CD-ROMs.

3.6.5 qemu-nbd Invocation

usage: qemu-nbd [OPTION]...  filename

Export Qemu disk image using NBD protocol.

@option{filename}
is a disk image filename
@option{-p, --port=port}
port to listen on (default `1024')
@option{-o, --offset=offset}
offset into the image
@option{-b, --bind=iface}
interface to bind to (default `0.0.0.0')
@option{-k, --socket=path}
Use a unix socket with path path
@option{-r, --read-only}
export read-only
@option{-P, --partition=num}
only expose partition num
@option{-s, --snapshot}
use snapshot file
@option{-n, --nocache}
disable host cache
@option{-c, --connect}
connect FILE to NBD device DEV
@option{-d, --disconnect}
disconnect the specified device
@option{-e, --shared=num}
device can be shared by num clients (default `1')
@option{-t, --persistent}
don't exit on the last connection
@option{-v, --verbose}
display extra debugging information
@option{-h, --help}
display this help and exit
@option{-V, --version}
output version information and exit

3.6.6 Using host drives

In addition to disk image files, QEMU can directly access host devices. We describe here the usage for QEMU version >= 0.8.3.

3.6.6.1 Linux

On Linux, you can directly use the host device filename instead of a disk image filename provided you have enough privileges to access it. For example, use `/dev/cdrom' to access to the CDROM or `/dev/fd0' for the floppy.

CD
You can specify a CDROM device even if no CDROM is loaded. QEMU has specific code to detect CDROM insertion or removal. CDROM ejection by the guest OS is supported. Currently only data CDs are supported.
Floppy
You can specify a floppy device even if no floppy is loaded. Floppy removal is currently not detected accurately (if you change floppy without doing floppy access while the floppy is not loaded, the guest OS will think that the same floppy is loaded).
Hard disks
Hard disks can be used. Normally you must specify the whole disk (`/dev/hdb' instead of `/dev/hdb1') so that the guest OS can see it as a partitioned disk. WARNING: unless you know what you do, it is better to only make READ-ONLY accesses to the hard disk otherwise you may corrupt your host data (use the @option{-snapshot} command line option or modify the device permissions accordingly).

3.6.6.2 Windows

CD
The preferred syntax is the drive letter (e.g. `d:'). The alternate syntax `\\.\d:' is supported. `/dev/cdrom' is supported as an alias to the first CDROM drive. Currently there is no specific code to handle removable media, so it is better to use the change or eject monitor commands to change or eject media.
Hard disks
Hard disks can be used with the syntax: `\\.\PhysicalDriveN' where N is the drive number (0 is the first hard disk). WARNING: unless you know what you do, it is better to only make READ-ONLY accesses to the hard disk otherwise you may corrupt your host data (use the @option{-snapshot} command line so that the modifications are written in a temporary file).

3.6.6.3 Mac OS X

`/dev/cdrom' is an alias to the first CDROM.

Currently there is no specific code to handle removable media, so it is better to use the change or eject monitor commands to change or eject media.

3.6.7 Virtual FAT disk images

QEMU can automatically create a virtual FAT disk image from a directory tree. In order to use it, just type: 

qemu linux.img -hdb fat:/my_directory

Then you access access to all the files in the `/my_directory' directory without having to copy them in a disk image or to export them via SAMBA or NFS. The default access is read-only.

Floppies can be emulated with the :floppy: option: 

qemu linux.img -fda fat:floppy:/my_directory

A read/write support is available for testing (beta stage) with the :rw: option: 

qemu linux.img -fda fat:floppy:rw:/my_directory

What you should never do:

3.6.8 NBD access

QEMU can access directly to block device exported using the Network Block Device protocol. 

qemu linux.img -hdb nbd:my_nbd_server.mydomain.org:1024

If the NBD server is located on the same host, you can use an unix socket instead of an inet socket: 

qemu linux.img -hdb nbd:unix:/tmp/my_socket

In this case, the block device must be exported using qemu-nbd: 

qemu-nbd --socket=/tmp/my_socket my_disk.qcow2

The use of qemu-nbd allows to share a disk between several guests: 

qemu-nbd --socket=/tmp/my_socket --share=2 my_disk.qcow2

and then you can use it with two guests: 

qemu linux1.img -hdb nbd:unix:/tmp/my_socket
qemu linux2.img -hdb nbd:unix:/tmp/my_socket

3.7 Network emulation

QEMU can simulate several network cards (PCI or ISA cards on the PC target) and can connect them to an arbitrary number of Virtual Local Area Networks (VLANs). Host TAP devices can be connected to any QEMU VLAN. VLAN can be connected between separate instances of QEMU to simulate large networks. For simpler usage, a non privileged user mode network stack can replace the TAP device to have a basic network connection.

3.7.1 VLANs

QEMU simulates several VLANs. A VLAN can be symbolised as a virtual connection between several network devices. These devices can be for example QEMU virtual Ethernet cards or virtual Host ethernet devices (TAP devices).

3.7.2 Using TAP network interfaces

This is the standard way to connect QEMU to a real network. QEMU adds a virtual network device on your host (called tapN), and you can then configure it as if it was a real ethernet card.

3.7.2.1 Linux host

As an example, you can download the `linux-test-xxx.tar.gz' archive and copy the script `qemu-ifup' in `/etc' and configure properly sudo so that the command ifconfig contained in `qemu-ifup' can be executed as root. You must verify that your host kernel supports the TAP network interfaces: the device `/dev/net/tun' must be present.

See section 3.3 Invocation to have examples of command lines using the TAP network interfaces.

3.7.2.2 Windows host

There is a virtual ethernet driver for Windows 2000/XP systems, called TAP-Win32. But it is not included in standard QEMU for Windows, so you will need to get it separately. It is part of OpenVPN package, so download OpenVPN from : http://openvpn.net/.

3.7.3 Using the user mode network stack

By using the option @option{-net user} (default configuration if no @option{-net} option is specified), QEMU uses a completely user mode network stack (you don't need root privilege to use the virtual network). The virtual network configuration is the following: 


         QEMU VLAN      <------>  Firewall/DHCP server <-----> Internet
                           |          (10.0.2.2)
                           |
                           ---->  DNS server (10.0.2.3)
                           |
                           ---->  SMB server (10.0.2.4)

The QEMU VM behaves as if it was behind a firewall which blocks all incoming connections. You can use a DHCP client to automatically configure the network in the QEMU VM. The DHCP server assign addresses to the hosts starting from 10.0.2.15.

In order to check that the user mode network is working, you can ping the address 10.0.2.2 and verify that you got an address in the range 10.0.2.x from the QEMU virtual DHCP server.

Note that ping is not supported reliably to the internet as it would require root privileges. It means you can only ping the local router (10.0.2.2).

When using the built-in TFTP server, the router is also the TFTP server.

When using the @option{-redir} option, TCP or UDP connections can be redirected from the host to the guest. It allows for example to redirect X11, telnet or SSH connections.

3.7.4 Connecting VLANs between QEMU instances

Using the @option{-net socket} option, it is possible to make VLANs that span several QEMU instances. See section 3.3 Invocation to have a basic example.

3.8 Direct Linux Boot

This section explains how to launch a Linux kernel inside QEMU without having to make a full bootable image. It is very useful for fast Linux kernel testing.

The syntax is: 

qemu -kernel arch/i386/boot/bzImage -hda root-2.4.20.img -append "root=/dev/hda"

Use @option{-kernel} to provide the Linux kernel image and @option{-append} to give the kernel command line arguments. The @option{-initrd} option can be used to provide an INITRD image.

When using the direct Linux boot, a disk image for the first hard disk `hda' is required because its boot sector is used to launch the Linux kernel.

If you do not need graphical output, you can disable it and redirect the virtual serial port and the QEMU monitor to the console with the @option{-nographic} option. The typical command line is: 

qemu -kernel arch/i386/boot/bzImage -hda root-2.4.20.img \
     -append "root=/dev/hda console=ttyS0" -nographic

Use Ctrl-a c to switch between the serial console and the monitor (see section 3.4 Keys).

3.9 USB emulation

QEMU emulates a PCI UHCI USB controller. You can virtually plug virtual USB devices or real host USB devices (experimental, works only on Linux hosts). Qemu will automatically create and connect virtual USB hubs as necessary to connect multiple USB devices.

3.9.1 Connecting USB devices

USB devices can be connected with the @option{-usbdevice} commandline option or the usb_add monitor command. Available devices are:

mouse
Virtual Mouse. This will override the PS/2 mouse emulation when activated.
tablet
Pointer device that uses absolute coordinates (like a touchscreen). This means qemu is able to report the mouse position without having to grab the mouse. Also overrides the PS/2 mouse emulation when activated.
disk:file
Mass storage device based on file (see section 3.6 Disk Images)
host:bus.addr
Pass through the host device identified by bus.addr (Linux only)
host:vendor_id:product_id
Pass through the host device identified by vendor_id:product_id (Linux only)
wacom-tablet
Virtual Wacom PenPartner tablet. This device is similar to the tablet above but it can be used with the tslib library because in addition to touch coordinates it reports touch pressure.
keyboard
Standard USB keyboard. Will override the PS/2 keyboard (if present).
serial:[vendorid=vendor_id][,product_id=product_id]:dev
Serial converter. This emulates an FTDI FT232BM chip connected to host character device dev. The available character devices are the same as for the -serial option. The vendorid and productid options can be used to override the default 0403:6001. For instance, 
usb_add serial:productid=FA00:tcp:192.168.0.2:4444
will connect to tcp port 4444 of ip 192.168.0.2, and plug that to the virtual serial converter, faking a Matrix Orbital LCD Display (USB ID 0403:FA00).
braille
Braille device. This will use BrlAPI to display the braille output on a real or fake device.
net:options
Network adapter that supports CDC ethernet and RNDIS protocols. options specifies NIC options as with -net nic,options (see description). For instance, user-mode networking can be used with 
qemu [...OPTIONS...] -net user,vlan=0 -usbdevice net:vlan=0
Currently this cannot be used in machines that support PCI NICs.
bt[:hci-type]
Bluetooth dongle whose type is specified in the same format as with the @option{-bt hci} option, @xref{bt-hcis,,allowed HCI types}. If no type is given, the HCI logic corresponds to -bt hci,vlan=0. This USB device implements the USB Transport Layer of HCI. Example usage: 
qemu [...OPTIONS...] -usbdevice bt:hci,vlan=3 -bt device:keyboard,vlan=3

3.9.2 Using host USB devices on a Linux host

WARNING: this is an experimental feature. QEMU will slow down when using it. USB devices requiring real time streaming (i.e. USB Video Cameras) are not supported yet.

  1. If you use an early Linux 2.4 kernel, verify that no Linux driver is actually using the USB device. A simple way to do that is simply to disable the corresponding kernel module by renaming it from `mydriver.o' to `mydriver.o.disabled'.
  2. Verify that `/proc/bus/usb' is working (most Linux distributions should enable it by default). You should see something like that: 
    ls /proc/bus/usb
001  devices  drivers
  3. Since only root can access to the USB devices directly, you can either launch QEMU as root or change the permissions of the USB devices you want to use. For testing, the following suffices: 
    chown -R myuid /proc/bus/usb
  4. Launch QEMU and do in the monitor: 
    info usbhost
  Device 1.2, speed 480 Mb/s
    Class 00: USB device 1234:5678, USB DISK
    You should see the list of the devices you can use (Never try to use hubs, it won't work).
  5. Add the device in QEMU by using: 
    usb_add host:1234:5678
    Normally the guest OS should report that a new USB device is plugged. You can use the option @option{-usbdevice} to do the same.
  6. Now you can try to use the host USB device in QEMU.

When relaunching QEMU, you may have to unplug and plug again the USB device to make it work again (this is a bug).

3.10 VNC security

The VNC server capability provides access to the graphical console of the guest VM across the network. This has a number of security considerations depending on the deployment scenarios.

3.10.1 Without passwords

The simplest VNC server setup does not include any form of authentication. For this setup it is recommended to restrict it to listen on a UNIX domain socket only. For example 

qemu [...OPTIONS...] -vnc unix:/home/joebloggs/.qemu-myvm-vnc

This ensures that only users on local box with read/write access to that path can access the VNC server. To securely access the VNC server from a remote machine, a combination of netcat+ssh can be used to provide a secure tunnel.

3.10.2 With passwords

The VNC protocol has limited support for password based authentication. Since the protocol limits passwords to 8 characters it should not be considered to provide high security. The password can be fairly easily brute-forced by a client making repeat connections. For this reason, a VNC server using password authentication should be restricted to only listen on the loopback interface or UNIX domain sockets. Password authentication is requested with the password option, and then once QEMU is running the password is set with the monitor. Until the monitor is used to set the password all clients will be rejected. 

qemu [...OPTIONS...] -vnc :1,password -monitor stdio
(qemu) change vnc password
Password: ********
(qemu)

3.10.3 With x509 certificates

The QEMU VNC server also implements the VeNCrypt extension allowing use of TLS for encryption of the session, and x509 certificates for authentication. The use of x509 certificates is strongly recommended, because TLS on its own is susceptible to man-in-the-middle attacks. Basic x509 certificate support provides a secure session, but no authentication. This allows any client to connect, and provides an encrypted session. 

qemu [...OPTIONS...] -vnc :1,tls,x509=/etc/pki/qemu -monitor stdio

In the above example /etc/pki/qemu should contain at least three files, ca-cert.pem, server-cert.pem and server-key.pem. Unprivileged users will want to use a private directory, for example $HOME/.pki/qemu. NB the server-key.pem file should be protected with file mode 0600 to only be readable by the user owning it.

3.10.4 With x509 certificates and client verification

Certificates can also provide a means to authenticate the client connecting. The server will request that the client provide a certificate, which it will then validate against the CA certificate. This is a good choice if deploying in an environment with a private internal certificate authority. 

qemu [...OPTIONS...] -vnc :1,tls,x509verify=/etc/pki/qemu -monitor stdio

3.10.5 With x509 certificates, client verification and passwords

Finally, the previous method can be combined with VNC password authentication to provide two layers of authentication for clients. 

qemu [...OPTIONS...] -vnc :1,password,tls,x509verify=/etc/pki/qemu -monitor stdio
(qemu) change vnc password
Password: ********
(qemu)

3.10.6 With SASL authentication

The SASL authentication method is a VNC extension, that provides an easily extendable, pluggable authentication method. This allows for integration with a wide range of authentication mechanisms, such as PAM, GSSAPI/Kerberos, LDAP, SQL databases, one-time keys and more. The strength of the authentication depends on the exact mechanism configured. If the chosen mechanism also provides a SSF layer, then it will encrypt the datastream as well.

Refer to the later docs on how to choose the exact SASL mechanism used for authentication, but assuming use of one supporting SSF, then QEMU can be launched with: 

qemu [...OPTIONS...] -vnc :1,sasl -monitor stdio

3.10.7 With x509 certificates and SASL authentication

If the desired SASL authentication mechanism does not supported SSF layers, then it is strongly advised to run it in combination with TLS and x509 certificates. This provides securely encrypted data stream, avoiding risk of compromising of the security credentials. This can be enabled, by combining the 'sasl' option with the aforementioned TLS + x509 options: 

qemu [...OPTIONS...] -vnc :1,tls,x509,sasl -monitor stdio

3.10.8 Generating certificates for VNC

The GNU TLS packages provides a command called certtool which can be used to generate certificates and keys in PEM format. At a minimum it is neccessary to setup a certificate authority, and issue certificates to each server. If using certificates for authentication, then each client will also need to be issued a certificate. The recommendation is for the server to keep its certificates in either /etc/pki/qemu or for unprivileged users in $HOME/.pki/qemu.

3.10.8.1 Setup the Certificate Authority

This step only needs to be performed once per organization / organizational unit. First the CA needs a private key. This key must be kept VERY secret and secure. If this key is compromised the entire trust chain of the certificates issued with it is lost. 

# certtool --generate-privkey > ca-key.pem

A CA needs to have a public certificate. For simplicity it can be a self-signed certificate, or one issue by a commercial certificate issuing authority. To generate a self-signed certificate requires one core piece of information, the name of the organization. 

# cat > ca.info <<EOF
cn = Name of your organization
ca
cert_signing_key
EOF
# certtool --generate-self-signed \
           --load-privkey ca-key.pem
           --template ca.info \
           --outfile ca-cert.pem

The ca-cert.pem file should be copied to all servers and clients wishing to utilize TLS support in the VNC server. The ca-key.pem must not be disclosed/copied at all.

3.10.8.2 Issuing server certificates

Each server (or host) needs to be issued with a key and certificate. When connecting the certificate is sent to the client which validates it against the CA certificate. The core piece of information for a server certificate is the hostname. This should be the fully qualified hostname that the client will connect with, since the client will typically also verify the hostname in the certificate. On the host holding the secure CA private key: 

# cat > server.info <<EOF
organization = Name  of your organization
cn = server.foo.example.com
tls_www_server
encryption_key
signing_key
EOF
# certtool --generate-privkey > server-key.pem
# certtool --generate-certificate \
           --load-ca-certificate ca-cert.pem \
           --load-ca-privkey ca-key.pem \
           --load-privkey server server-key.pem \
           --template server.info \
           --outfile server-cert.pem

The server-key.pem and server-cert.pem files should now be securely copied to the server for which they were generated. The server-key.pem is security sensitive and should be kept protected with file mode 0600 to prevent disclosure.

3.10.8.3 Issuing client certificates

If the QEMU VNC server is to use the x509verify option to validate client certificates as its authentication mechanism, each client also needs to be issued a certificate. The client certificate contains enough metadata to uniquely identify the client, typically organization, state, city, building, etc. On the host holding the secure CA private key: 

# cat > client.info <<EOF
country = GB
state = London
locality = London
organiazation = Name of your organization
cn = client.foo.example.com
tls_www_client
encryption_key
signing_key
EOF
# certtool --generate-privkey > client-key.pem
# certtool --generate-certificate \
           --load-ca-certificate ca-cert.pem \
           --load-ca-privkey ca-key.pem \
           --load-privkey client-key.pem \
           --template client.info \
           --outfile client-cert.pem

The client-key.pem and client-cert.pem files should now be securely copied to the client for which they were generated.

3.10.9 Configuring SASL mechanisms

The following documentation assumes use of the Cyrus SASL implementation on a Linux host, but the principals should apply to any other SASL impl. When SASL is enabled, the mechanism configuration will be loaded from system default SASL service config /etc/sasl2/qemu.conf. If running QEMU as an unprivileged user, an environment variable SASL_CONF_PATH can be used to make it search alternate locations for the service config.

The default configuration might contain 

mech_list: digest-md5
sasldb_path: /etc/qemu/passwd.db

This says to use the 'Digest MD5' mechanism, which is similar to the HTTP Digest-MD5 mechanism. The list of valid usernames & passwords is maintained in the /etc/qemu/passwd.db file, and can be updated using the saslpasswd2 command. While this mechanism is easy to configure and use, it is not considered secure by modern standards, so only suitable for developers / ad-hoc testing.

A more serious deployment might use Kerberos, which is done with the 'gssapi' mechanism 

mech_list: gssapi
keytab: /etc/qemu/krb5.tab

For this to work the administrator of your KDC must generate a Kerberos principal for the server, with a name of 'qemu/somehost.example.com@EXAMPLE.COM' replacing 'somehost.example.com' with the fully qualified host name of the machine running QEMU, and 'EXAMPLE.COM' with the Keberos Realm.

Other configurations will be left as an exercise for the reader. It should be noted that only Digest-MD5 and GSSAPI provides a SSF layer for data encryption. For all other mechanisms, VNC should always be configured to use TLS and x509 certificates to protect security credentials from snooping.

3.11 GDB usage

QEMU has a primitive support to work with gdb, so that you can do 'Ctrl-C' while the virtual machine is running and inspect its state.

In order to use gdb, launch qemu with the '-s' option. It will wait for a gdb connection: 

> qemu -s -kernel arch/i386/boot/bzImage -hda root-2.4.20.img \
       -append "root=/dev/hda"
Connected to host network interface: tun0
Waiting gdb connection on port 1234

Then launch gdb on the 'vmlinux' executable: 

> gdb vmlinux

In gdb, connect to QEMU: 

(gdb) target remote localhost:1234

Then you can use gdb normally. For example, type 'c' to launch the kernel: 

(gdb) c

Here are some useful tips in order to use gdb on system code:

  1. Use info reg to display all the CPU registers.
  2. Use x/10i $eip to display the code at the PC position.
  3. Use set architecture i8086 to dump 16 bit code. Then use x/10i $cs*16+$eip to dump the code at the PC position.

Advanced debugging options:

The default single stepping behavior is step with the IRQs and timer service routines off. It is set this way because when gdb executes a single step it expects to advance beyond the current instruction. With the IRQs and and timer service routines on, a single step might jump into the one of the interrupt or exception vectors instead of executing the current instruction. This means you may hit the same breakpoint a number of times before executing the instruction gdb wants to have executed. Because there are rare circumstances where you want to single step into an interrupt vector the behavior can be controlled from GDB. There are three commands you can query and set the single step behavior:

maintenance packet qqemu.sstepbits
This will display the MASK bits used to control the single stepping IE: 
(gdb) maintenance packet qqemu.sstepbits
sending: "qqemu.sstepbits"
received: "ENABLE=1,NOIRQ=2,NOTIMER=4"
maintenance packet qqemu.sstep
This will display the current value of the mask used when single stepping IE: 
(gdb) maintenance packet qqemu.sstep
sending: "qqemu.sstep"
received: "0x7"
maintenance packet Qqemu.sstep=HEX_VALUE
This will change the single step mask, so if wanted to enable IRQs on the single step, but not timers, you would use: 
(gdb) maintenance packet Qqemu.sstep=0x5
sending: "qemu.sstep=0x5"
received: "OK"

3.12 Target OS specific information

3.12.1 Linux

To have access to SVGA graphic modes under X11, use the vesa or the cirrus X11 driver. For optimal performances, use 16 bit color depth in the guest and the host OS.

When using a 2.6 guest Linux kernel, you should add the option clock=pit on the kernel command line because the 2.6 Linux kernels make very strict real time clock checks by default that QEMU cannot simulate exactly.

When using a 2.6 guest Linux kernel, verify that the 4G/4G patch is not activated because QEMU is slower with this patch. The QEMU Accelerator Module is also much slower in this case. Earlier Fedora Core 3 Linux kernel (< 2.6.9-1.724_FC3) were known to incorporate this patch by default. Newer kernels don't have it.

3.12.2 Windows

If you have a slow host, using Windows 95 is better as it gives the best speed. Windows 2000 is also a good choice.

3.12.2.1 SVGA graphic modes support

QEMU emulates a Cirrus Logic GD5446 Video card. All Windows versions starting from Windows 95 should recognize and use this graphic card. For optimal performances, use 16 bit color depth in the guest and the host OS.

If you are using Windows XP as guest OS and if you want to use high resolution modes which the Cirrus Logic BIOS does not support (i.e. >= 1280x1024x16), then you should use the VESA VBE virtual graphic card (option @option{-std-vga}).

3.12.2.2 CPU usage reduction

Windows 9x does not correctly use the CPU HLT instruction. The result is that it takes host CPU cycles even when idle. You can install the utility from http://www.user.cityline.ru/~maxamn/amnhltm.zip to solve this problem. Note that no such tool is needed for NT, 2000 or XP.

3.12.2.3 Windows 2000 disk full problem

Windows 2000 has a bug which gives a disk full problem during its installation. When installing it, use the @option{-win2k-hack} QEMU option to enable a specific workaround. After Windows 2000 is installed, you no longer need this option (this option slows down the IDE transfers).

3.12.2.4 Windows 2000 shutdown

Windows 2000 cannot automatically shutdown in QEMU although Windows 98 can. It comes from the fact that Windows 2000 does not automatically use the APM driver provided by the BIOS.

In order to correct that, do the following (thanks to Struan Bartlett): go to the Control Panel => Add/Remove Hardware & Next => Add/Troubleshoot a device => Add a new device & Next => No, select the hardware from a list & Next => NT Apm/Legacy Support & Next => Next (again) a few times. Now the driver is installed and Windows 2000 now correctly instructs QEMU to shutdown at the appropriate moment.

3.12.2.5 Share a directory between Unix and Windows

See section 3.3 Invocation about the help of the option @option{-smb}.

3.12.2.6 Windows XP security problem

Some releases of Windows XP install correctly but give a security error when booting: 

A problem is preventing Windows from accurately checking the
license for this computer. Error code: 0x800703e6.

The workaround is to install a service pack for XP after a boot in safe mode. Then reboot, and the problem should go away. Since there is no network while in safe mode, its recommended to download the full installation of SP1 or SP2 and transfer that via an ISO or using the vvfat block device ("-hdb fat:directory_which_holds_the_SP").

3.12.3 MS-DOS and FreeDOS

3.12.3.1 CPU usage reduction

DOS does not correctly use the CPU HLT instruction. The result is that it takes host CPU cycles even when idle. You can install the utility from http://www.vmware.com/software/dosidle210.zip to solve this problem.

4. QEMU System emulator for non PC targets

QEMU is a generic emulator and it emulates many non PC machines. Most of the options are similar to the PC emulator. The differences are mentioned in the following sections.

4.1 QEMU PowerPC System emulator

Use the executable `qemu-system-ppc' to simulate a complete PREP or PowerMac PowerPC system.

QEMU emulates the following PowerMac peripherals:

QEMU emulates the following PREP peripherals:

QEMU uses the Open Hack'Ware Open Firmware Compatible BIOS available at http://perso.magic.fr/l_indien/OpenHackWare/index.htm.

Since version 0.9.1, QEMU uses OpenBIOS http://www.openbios.org/ for the g3beige and mac99 PowerMac machines. OpenBIOS is a free (GPL v2) portable firmware implementation. The goal is to implement a 100% IEEE 1275-1994 (referred to as Open Firmware) compliant firmware.

The following options are specific to the PowerPC emulation:

@option{-g WxH[xDEPTH]}
Set the initial VGA graphic mode. The default is 800x600x15.
@option{-prom-env string}
Set OpenBIOS variables in NVRAM, for example: 
qemu-system-ppc -prom-env 'auto-boot?=false' \
 -prom-env 'boot-device=hd:2,\yaboot' \
 -prom-env 'boot-args=conf=hd:2,\yaboot.conf'
These variables are not used by Open Hack'Ware.

More information is available at http://perso.magic.fr/l_indien/qemu-ppc/.

4.2 Sparc32 System emulator

Use the executable `qemu-system-sparc' to simulate the following Sun4m architecture machines:

The emulation is somewhat complete. SMP up to 16 CPUs is supported, but Linux limits the number of usable CPUs to 4.

It's also possible to simulate a SPARCstation 2 (sun4c architecture), SPARCserver 1000, or SPARCcenter 2000 (sun4d architecture), but these emulators are not usable yet.

QEMU emulates the following sun4m/sun4c/sun4d peripherals:

The number of peripherals is fixed in the architecture. Maximum memory size depends on the machine type, for SS-5 it is 256MB and for others 2047MB.

Since version 0.8.2, QEMU uses OpenBIOS http://www.openbios.org/. OpenBIOS is a free (GPL v2) portable firmware implementation. The goal is to implement a 100% IEEE 1275-1994 (referred to as Open Firmware) compliant firmware.

A sample Linux 2.6 series kernel and ram disk image are available on the QEMU web site. There are still issues with NetBSD and OpenBSD, but some kernel versions work. Please note that currently Solaris kernels don't work probably due to interface issues between OpenBIOS and Solaris.

The following options are specific to the Sparc32 emulation:

@option{-g WxHx[xDEPTH]}
Set the initial TCX graphic mode. The default is 1024x768x8, currently the only other possible mode is 1024x768x24.
@option{-prom-env string}
Set OpenBIOS variables in NVRAM, for example: 
qemu-system-sparc -prom-env 'auto-boot?=false' \
 -prom-env 'boot-device=sd(0,2,0):d' -prom-env 'boot-args=linux single'
@option{-M [SS-4|SS-5|SS-10|SS-20|SS-600MP|LX|Voyager|SPARCClassic|SPARCbook|SS-2|SS-1000|SS-2000]}
Set the emulated machine type. Default is SS-5.

4.3 Sparc64 System emulator

Use the executable `qemu-system-sparc64' to simulate a Sun4u (UltraSPARC PC-like machine), Sun4v (T1 PC-like machine), or generic Niagara (T1) machine. The emulator is not usable for anything yet, but it can launch some kernels.

QEMU emulates the following peripherals:

The following options are specific to the Sparc64 emulation:

@option{-prom-env string}
Set OpenBIOS variables in NVRAM, for example: 
qemu-system-sparc64 -prom-env 'auto-boot?=false'
@option{-M [sun4u|sun4v|Niagara]}
Set the emulated machine type. The default is sun4u.

4.4 MIPS System emulator

Four executables cover simulation of 32 and 64-bit MIPS systems in both endian options, `qemu-system-mips', `qemu-system-mipsel' `qemu-system-mips64' and `qemu-system-mips64el'. Five different machine types are emulated:

The generic emulation is supported by Debian 'Etch' and is able to install Debian into a virtual disk image. The following devices are emulated:

The Malta emulation supports the following devices:

The ACER Pica emulation supports:

The mipssim pseudo board emulation provides an environment similiar to what the proprietary MIPS emulator uses for running Linux. It supports:

The MIPS Magnum R4000 emulation supports:

4.5 ARM System emulator

Use the executable `qemu-system-arm' to simulate a ARM machine. The ARM Integrator/CP board is emulated with the following devices:

The ARM Versatile baseboard is emulated with the following devices:

The ARM RealView Emulation/Platform baseboard is emulated with the following devices:

The XScale-based clamshell PDA models ("Spitz", "Akita", "Borzoi" and "Terrier") emulation includes the following peripherals:

The Palm Tungsten|E PDA (codename "Cheetah") emulation includes the following elements:

Nokia N800 and N810 internet tablets (known also as RX-34 and RX-44 / 48) emulation supports the following elements:

The Luminary Micro Stellaris LM3S811EVB emulation includes the following devices:

The Luminary Micro Stellaris LM3S6965EVB emulation includes the following devices:

The Freecom MusicPal internet radio emulation includes the following elements:

The Siemens SX1 models v1 and v2 (default) basic emulation. The emulaton includes the following elements:

The "Syborg" Symbian Virtual Platform base model includes the following elements:

A Linux 2.6 test image is available on the QEMU web site. More information is available in the QEMU mailing-list archive.

The following options are specific to the ARM emulation:

@option{-semihosting}
Enable semihosting syscall emulation. On ARM this implements the "Angel" interface. Note that this allows guest direct access to the host filesystem, so should only be used with trusted guest OS.

4.6 ColdFire System emulator

Use the executable `qemu-system-m68k' to simulate a ColdFire machine. The emulator is able to boot a uClinux kernel.

The M5208EVB emulation includes the following devices:

The AN5206 emulation includes the following devices:

The following options are specific to the ARM emulation:

@option{-semihosting}
Enable semihosting syscall emulation. On M68K this implements the "ColdFire GDB" interface used by libgloss. Note that this allows guest direct access to the host filesystem, so should only be used with trusted guest OS.

5. QEMU User space emulator

5.1 Supported Operating Systems

The following OS are supported in user space emulation:

5.2 Linux User space emulator

5.2.1 Quick Start

In order to launch a Linux process, QEMU needs the process executable itself and all the target (x86) dynamic libraries used by it.

5.2.2 Wine launch

5.2.3 Command line options

usage: qemu-i386 [-h] [-d] [-L path] [-s size] [-cpu model] [-g port] [-B offset] program [arguments...]
@option{-h}
Print the help
@option{-L path}
Set the x86 elf interpreter prefix (default=/usr/local/qemu-i386)
@option{-s size}
Set the x86 stack size in bytes (default=524288)
@option{-cpu model}
Select CPU model (-cpu ? for list and additional feature selection)
@option{-B offset}
Offset guest address by the specified number of bytes. This is useful when the address region rewuired by guest applications is reserved on the host. Ths option is currently only supported on some hosts.

Debug options:

@option{-d}
Activate log (logfile=/tmp/qemu.log)
@option{-p pagesize}
Act as if the host page size was 'pagesize' bytes
@option{-g port}
Wait gdb connection to port
@option{-singlestep}
Run the emulation in single step mode.

Environment variables:

@env{QEMU_STRACE}
Print system calls and arguments similar to the 'strace' program (NOTE: the actual 'strace' program will not work because the user space emulator hasn't implemented ptrace). At the moment this is incomplete. All system calls that don't have a specific argument format are printed with information for six arguments. Many flag-style arguments don't have decoders and will show up as numbers.

5.2.4 Other binaries

@command{qemu-arm} is also capable of running ARM "Angel" semihosted ELF binaries (as implemented by the arm-elf and arm-eabi Newlib/GDB configurations), and arm-uclinux bFLT format binaries.

@command{qemu-m68k} is capable of running semihosted binaries using the BDM (m5xxx-ram-hosted.ld) or m68k-sim (sim.ld) syscall interfaces, and coldfire uClinux bFLT format binaries.

The binary format is detected automatically.

@command{qemu-sparc} can execute Sparc32 binaries (Sparc32 CPU, 32 bit ABI).

@command{qemu-sparc32plus} can execute Sparc32 and SPARC32PLUS binaries (Sparc64 CPU, 32 bit ABI).

@command{qemu-sparc64} can execute some Sparc64 (Sparc64 CPU, 64 bit ABI) and SPARC32PLUS binaries (Sparc64 CPU, 32 bit ABI).

5.3 Mac OS X/Darwin User space emulator

5.3.1 Mac OS X/Darwin Status

[1] If you're host commpage can be executed by qemu.

5.3.2 Quick Start

In order to launch a Mac OS X/Darwin process, QEMU needs the process executable itself and all the target dynamic libraries used by it. If you don't have the FAT libraries (you're running Mac OS X/ppc) you'll need to obtain it from a Mac OS X CD or compile them by hand.

5.3.3 Command line options

usage: qemu-i386 [-h] [-d] [-L path] [-s size] program [arguments...]
@option{-h}
Print the help
@option{-L path}
Set the library root path (default=/)
@option{-s size}
Set the stack size in bytes (default=524288)

Debug options:

@option{-d}
Activate log (logfile=/tmp/qemu.log)
@option{-p pagesize}
Act as if the host page size was 'pagesize' bytes
@option{-singlestep}
Run the emulation in single step mode.

5.4 BSD User space emulator

5.4.1 BSD Status

5.4.2 Quick Start

In order to launch a BSD process, QEMU needs the process executable itself and all the target dynamic libraries used by it.

5.4.3 Command line options

usage: qemu-sparc64 [-h] [-d] [-L path] [-s size] [-bsd type] program [arguments...]
@option{-h}
Print the help
@option{-L path}
Set the library root path (default=/)
@option{-s size}
Set the stack size in bytes (default=524288)
@option{-bsd type}
Set the type of the emulated BSD Operating system. Valid values are FreeBSD, NetBSD and OpenBSD (default).

Debug options:

@option{-d}
Activate log (logfile=/tmp/qemu.log)
@option{-p pagesize}
Act as if the host page size was 'pagesize' bytes
@option{-singlestep}
Run the emulation in single step mode.

6. Compilation from the sources

6.1 Linux/Unix

6.1.1 Compilation

First you must decompress the sources: 

cd /tmp
tar zxvf qemu-x.y.z.tar.gz
cd qemu-x.y.z

Then you configure QEMU and build it (usually no options are needed): 

./configure
make

Then type as root user: 

make install

to install QEMU in `/usr/local'.

6.2 Windows

6.3 Cross compilation for Windows with Linux

Note: Currently, Wine does not seem able to launch QEMU for Win32.

6.4 Mac OS X

The Mac OS X patches are not fully merged in QEMU, so you should look at the QEMU mailing list archive to have all the necessary information.

7. Index

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