accel=accels1[:accels2[:...]]

This is used to enable an accelerator. Depending on the target architecture, kvm, xen, hax, hvf, whpx or tcg can be available. By default, tcg is used. If there is more than one accelerator specified, the next one is used if the previous one fails to initialize.

kernel_irqchip=on|off

Controls in-kernel irqchip support for the chosen accelerator when available.

gfx_passthru=on|off

Enables IGD GFX passthrough support for the chosen machine when available.

vmport=on|off|auto

Enables emulation of VMWare IO port, for vmmouse etc. auto says to select the value based on accel. For accel=xen the default is off otherwise the default is on.

kvm_shadow_mem=size

Defines the size of the KVM shadow MMU.

dump-guest-core=on|off

Include guest memory in a core dump. The default is on.

mem-merge=on|off

Enables or disables memory merge support. This feature, when supported by the host, de-duplicates identical memory pages among VMs instances (enabled by default).

aes-key-wrap=on|off

Enables or disables AES key wrapping support on s390-ccw hosts. This feature controls whether AES wrapping keys will be created to allow execution of AES cryptographic functions. The default is on.

dea-key-wrap=on|off

Enables or disables DEA key wrapping support on s390-ccw hosts. This feature controls whether DEA wrapping keys will be created to allow execution of DEA cryptographic functions. The default is on.

nvdimm=on|off

Enables or disables NVDIMM support. The default is off.

enforce-config-section=on|off

If enforce-config-section is set to on, force migration code to send configuration section even if the machine-type sets the migration.send-configuration property to off. NOTE: this parameter is deprecated. Please use -global migration.send-configuration=on|off instead.

memory-encryption=

Memory encryption object to use. The default is none.

thread=single|multi

Controls number of TCG threads. When the TCG is multi-threaded there will be one thread per vCPU therefor taking advantage of additional host cores. The default is to enable multi-threading where both the back-end and front-ends support it and no incompatible TCG features have been enabled (e.g. icount/replay).

fd=fd

This option defines the file descriptor of which a duplicate is added to fd set. The file descriptor cannot be stdin, stdout, or stderr.

set=set

This option defines the ID of the fd set to add the file descriptor to.

opaque=opaque

This option defines a free-form string that can be used to describe fd.

You can open an image using pre-opened file descriptors from an fd set:

        qemu-system-i386
        -add-fd fd=3,set=2,opaque="rdwr:/path/to/file"
        -add-fd fd=4,set=2,opaque="rdonly:/path/to/file"
        -drive file=/dev/fdset/2,index=0,media=disk

bmc=id

The BMC to connect to, one of ipmi-bmc-sim or ipmi-bmc-extern above.

slave_addr=val

Define slave address to use for the BMC. The default is 0x20.

sdrfile=file

file containing raw Sensor Data Records (SDR) data. The default is none.

fruareasize=val

size of a Field Replaceable Unit (FRU) area. The default is 1024.

frudatafile=file

file containing raw Field Replaceable Unit (FRU) inventory data. The default is none.

bmc=id

The BMC to connect to, one of ipmi-bmc-sim or ipmi-bmc-extern above.

ioport=val

Define the I/O address of the interface. The default is 0xca0 for KCS.

irq=val

Define the interrupt to use. The default is 5. To disable interrupts, set this to 0.

Valid options for any block driver node:

Driver-specific options for "file"

This is the protocol-level block driver for accessing regular files.

        -blockdev driver=file,node-name=disk,filename=disk.img

Driver-specific options for "raw"

This is the image format block driver for raw images. It is usually stacked on top of a protocol level block driver such as "file".

        -blockdev driver=file,node-name=disk_file,filename=disk.img
        -blockdev driver=raw,node-name=disk,file=disk_file

        -blockdev driver=raw,node-name=disk,file.driver=file,file.filename=disk.img

Driver-specific options for "qcow2"

This is the image format block driver for qcow2 images. It is usually stacked on top of a protocol level block driver such as "file".

        -blockdev driver=file,node-name=my_file,filename=/tmp/disk.qcow2
        -blockdev driver=qcow2,node-name=hda,file=my_file,overlap-check=none,cache-size=16777216

        -blockdev driver=qcow2,node-name=disk,file.driver=http,file.filename=http://example.com/image.qcow2

Driver-specific options for other drivers

Please refer to the QAPI documentation of the "blockdev-add" QMP command.

file=file

This option defines which disk image to use with this drive. If the filename contains comma, you must double it (for instance, "file=my,,file" to use file "my,file").

Special files such as iSCSI devices can be specified using protocol specific URLs. See the section for "Device URL Syntax" for more information.

if=interface

This option defines on which type on interface the drive is connected. Available types are: ide, scsi, sd, mtd, floppy, pflash, virtio, none.

bus=bus,unit=unit

These options define where is connected the drive by defining the bus number and the unit id.

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.

media=media

This option defines the type of the media: disk or cdrom.

snapshot=snapshot

snapshot is "on" or "off" and controls snapshot mode for the given drive (see -snapshot).

cache=cache

cache is "none", "writeback", "unsafe", "directsync" or "writethrough" and controls how the host cache is used to access block data. This is a shortcut that sets the cache.direct and cache.no-flush options (as in -blockdev), and additionally cache.writeback, which provides a default for the write-cache option of block guest devices (as in -device). The modes correspond to the following settings:

                     │ cache.writeback   cache.direct   cache.no-flush
        ─────────────┼─────────────────────────────────────────────────
        writeback    │ on                off            off
        none         │ on                on             off
        writethrough │ off               off            off
        directsync   │ off               on             off
        unsafe       │ on                off            on
    

The default mode is cache=writeback.

aio=aio

aio is "threads", or "native" and selects between pthread based disk I/O and native Linux AIO.

format=format

Specify which disk format will be used rather than detecting the format. Can be used to specify format=raw to avoid interpreting an untrusted format header.

werror=action,rerror=action

Specify which action to take on write and read errors. Valid actions are: "ignore" (ignore the error and try to continue), "stop" (pause QEMU), "report" (report the error to the guest), "enospc" (pause QEMU only if the host disk is full; report the error to the guest otherwise). The default setting is werror=enospc and rerror=report.

copy-on-read=copy-on-read

copy-on-read is "on" or "off" and enables whether to copy read backing file sectors into the image file.

bps=b,bps_rd=r,bps_wr=w

Specify bandwidth throttling limits in bytes per second, either for all request types or for reads or writes only. Small values can lead to timeouts or hangs inside the guest. A safe minimum for disks is 2 MB/s.

bps_max=bm,bps_rd_max=rm,bps_wr_max=wm

Specify bursts in bytes per second, either for all request types or for reads or writes only. Bursts allow the guest I/O to spike above the limit temporarily.

iops=i,iops_rd=r,iops_wr=w

Specify request rate limits in requests per second, either for all request types or for reads or writes only.

iops_max=bm,iops_rd_max=rm,iops_wr_max=wm

Specify bursts in requests per second, either for all request types or for reads or writes only. Bursts allow the guest I/O to spike above the limit temporarily.

iops_size=is

Let every is bytes of a request count as a new request for iops throttling purposes. Use this option to prevent guests from circumventing iops limits by sending fewer but larger requests.

group=g

Join a throttling quota group with given name g. All drives that are members of the same group are accounted for together. Use this option to prevent guests from circumventing throttling limits by using many small disks instead of a single larger disk.

By default, the cache.writeback=on mode is used. It will report data writes as completed as soon as the data is present in the host page cache. This is safe as long as your guest OS makes sure to correctly flush disk caches where needed. If your guest OS does not handle volatile disk write caches correctly and your host crashes or loses power, then the guest may experience data corruption.

For such guests, you should consider using cache.writeback=off. 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 after QEMU has made sure to flush each write to the disk. Be aware that this has a major impact on performance.

When using the -snapshot option, unsafe caching is always used.

Copy-on-read avoids accessing the same backing file sectors repeatedly and is useful when the backing file is over a slow network. By default copy-on-read is off.

Instead of -cdrom you can use:

        qemu-system-i386 -drive file=file,index=2,media=cdrom

Instead of -hda, -hdb, -hdc, -hdd, you can use:

        qemu-system-i386 -drive file=file,index=0,media=disk
        qemu-system-i386 -drive file=file,index=1,media=disk
        qemu-system-i386 -drive file=file,index=2,media=disk
        qemu-system-i386 -drive file=file,index=3,media=disk

You can open an image using pre-opened file descriptors from an fd set:

        qemu-system-i386
        -add-fd fd=3,set=2,opaque="rdwr:/path/to/file"
        -add-fd fd=4,set=2,opaque="rdonly:/path/to/file"
        -drive file=/dev/fdset/2,index=0,media=disk

You can connect a CDROM to the slave of ide0:

        qemu-system-i386 -drive file=file,if=ide,index=1,media=cdrom

If you don't specify the "file=" argument, you define an empty drive:

        qemu-system-i386 -drive if=ide,index=1,media=cdrom

Instead of -fda, -fdb, you can use:

        qemu-system-i386 -drive file=file,index=0,if=floppy
        qemu-system-i386 -drive file=file,index=1,if=floppy

By default, interface is "ide" and index is automatically incremented:

        qemu-system-i386 -drive file=a -drive file=b"

is interpreted like:

        qemu-system-i386 -hda a -hdb b

fsdriver

This option specifies the fs driver backend to use. Currently "local", "handle" and "proxy" file system drivers are supported.

id=id

Specifies identifier for this device

path=path

Specifies the export path for the file system device. Files under this path will be available to the 9p client on the guest.

security_model=security_model

Specifies the security model to be used for this export path. Supported security models are "passthrough", "mapped-xattr", "mapped-file" and "none". In "passthrough" security model, files are stored using the same credentials as they are created on the guest. This requires QEMU to run as root. In "mapped-xattr" security model, some of the file attributes like uid, gid, mode bits and link target are stored as file attributes. For "mapped-file" these attributes are stored in the hidden .virtfs_metadata directory. Directories exported by this security model cannot interact with other unix tools. "none" security model is same as passthrough except the sever won't report failures if it fails to set file attributes like ownership. Security model is mandatory only for local fsdriver. Other fsdrivers (like handle, proxy) don't take security model as a parameter.

writeout=writeout

This is an optional argument. The only supported value is "immediate". This means that 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.

readonly

Enables exporting 9p share as a readonly mount for guests. By default read-write access is given.

socket=socket

Enables proxy filesystem driver to use passed socket file for communicating with virtfs-proxy-helper

sock_fd=sock_fd

Enables proxy filesystem driver to use passed socket descriptor for communicating with virtfs-proxy-helper. Usually a helper like libvirt will create socketpair and pass one of the fds as sock_fd

fmode=fmode

Specifies the default mode for newly created files on the host. Works only with security models "mapped-xattr" and "mapped-file".

dmode=dmode

Specifies the default mode for newly created directories on the host. Works only with security models "mapped-xattr" and "mapped-file".

-fsdev option is used along with -device driver "virtio-9p-pci".

fsdev=id

Specifies the id value specified along with -fsdev option

mount_tag=mount_tag

Specifies the tag name to be used by the guest to mount this export point

fsdriver

This option specifies the fs driver backend to use. Currently "local", "handle" and "proxy" file system drivers are supported.

id=id

Specifies identifier for this device

path=path

Specifies the export path for the file system device. Files under this path will be available to the 9p client on the guest.

security_model=security_model

Specifies the security model to be used for this export path. Supported security models are "passthrough", "mapped-xattr", "mapped-file" and "none". In "passthrough" security model, files are stored using the same credentials as they are created on the guest. This requires QEMU to run as root. In "mapped-xattr" security model, some of the file attributes like uid, gid, mode bits and link target are stored as file attributes. For "mapped-file" these attributes are stored in the hidden .virtfs_metadata directory. Directories exported by this security model cannot interact with other unix tools. "none" security model is same as passthrough except the sever won't report failures if it fails to set file attributes like ownership. Security model is mandatory only for local fsdriver. Other fsdrivers (like handle, proxy) don't take security model as a parameter.

writeout=writeout

This is an optional argument. The only supported value is "immediate". This means that 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.

readonly

Enables exporting 9p share as a readonly mount for guests. By default read-write access is given.

socket=socket

Enables proxy filesystem driver to use passed socket file for communicating with virtfs-proxy-helper. Usually a helper like libvirt will create socketpair and pass one of the fds as sock_fd

sock_fd

Enables proxy filesystem driver to use passed 'sock_fd' as the socket descriptor for interfacing with virtfs-proxy-helper

fmode=fmode

Specifies the default mode for newly created files on the host. Works only with security models "mapped-xattr" and "mapped-file".

dmode=dmode

Specifies the default mode for newly created directories on the host. Works only with security models "mapped-xattr" and "mapped-file".

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.

braille

Braille device. This will use BrlAPI to display the braille output on a real or fake device.

sdl

Display video output via SDL (usually in a separate graphics window; see the SDL documentation for other possibilities).

curses

Display video output via curses. For graphics device models which support a text mode, QEMU can display this output using a curses/ncurses interface. Nothing is displayed when the graphics device is in graphical mode or if the graphics device does not support a text mode. Generally only the VGA device models support text mode.

none

Do not display video output. The guest will still see an emulated graphics card, but its output will not be displayed to the QEMU user. This option differs from the -nographic option in that it only affects what is done with video output; -nographic also changes the destination of the serial and parallel port data.

gtk

Display video output in a GTK window. This interface provides drop-down menus and other UI elements to configure and control the VM during runtime.

vnc

Start a VNC server on display <arg>

egl-headless

Offload all OpenGL operations to a local DRI device. For any graphical display, this display needs to be paired with either VNC or SPICE displays.

port=<nr>

Set the TCP port spice is listening on for plaintext channels.

addr=<addr>

Set the IP address spice is listening on. Default is any address.

ipv4

ipv6

unix

Force using the specified IP version.

password=<secret>

Set the password you need to authenticate.

sasl

Require that the client use SASL to authenticate with the spice. 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.

disable-ticketing

Allow client connects without authentication.

disable-copy-paste

Disable copy paste between the client and the guest.

disable-agent-file-xfer

Disable spice-vdagent based file-xfer between the client and the guest.

tls-port=<nr>

Set the TCP port spice is listening on for encrypted channels.

x509-dir=<dir>

Set the x509 file directory. Expects same filenames as -vnc $display,x509=$dir

x509-key-file=<file>

x509-key-password=<file>

x509-cert-file=<file>

x509-cacert-file=<file>

x509-dh-key-file=<file>

The x509 file names can also be configured individually.

tls-ciphers=<list>

Specify which ciphers to use.

tls-channel=[main|display|cursor|inputs|record|playback]

plaintext-channel=[main|display|cursor|inputs|record|playback]

Force specific channel to be used with or without TLS encryption. The options can be specified multiple times to configure multiple channels. The special name "default" can be used to set the default mode. For channels which are not explicitly forced into one mode the spice client is allowed to pick tls/plaintext as he pleases.

image-compression=[auto_glz|auto_lz|quic|glz|lz|off]

Configure image compression (lossless). Default is auto_glz.

jpeg-wan-compression=[auto|never|always]

zlib-glz-wan-compression=[auto|never|always]

Configure wan image compression (lossy for slow links). Default is auto.

streaming-video=[off|all|filter]

Configure video stream detection. Default is off.

agent-mouse=[on|off]

Enable/disable passing mouse events via vdagent. Default is on.

playback-compression=[on|off]

Enable/disable audio stream compression (using celt 0.5.1). Default is on.

seamless-migration=[on|off]

Enable/disable spice seamless migration. Default is off.

gl=[on|off]

Enable/disable OpenGL context. Default is off.

rendernode=<file>

DRM render node for OpenGL rendering. If not specified, it will pick the first available. (Since 2.9)

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 card was the default before QEMU 2.2)

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. (This card is the default since QEMU 2.2)

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.

qxl

QXL paravirtual graphic card. It is VGA compatible (including VESA 2.0 VBE support). Works best with qxl guest drivers installed though. Recommended choice when using the spice protocol.

tcx

(sun4m only) Sun TCX framebuffer. This is the default framebuffer for sun4m machines and offers both 8-bit and 24-bit colour depths at a fixed resolution of 1024x768.

cg3

(sun4m only) Sun cgthree framebuffer. This is a simple 8-bit framebuffer for sun4m machines available in both 1024x768 (OpenBIOS) and 1152x900 (OBP) resolutions aimed at people wishing to run older Solaris versions.

virtio

Virtio VGA card.

none

Disable VGA card.

to=L

With this option, QEMU will try next available VNC displays, until the number L, if the origianlly defined "-vnc display" is not available, e.g. port 5900+display is already used by another application. By default, to=0.

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.

unix:path

Connections will be allowed over UNIX domain sockets where path is the location of a unix socket to listen for connections on.

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

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.

websocket

Opens an additional TCP listening port dedicated to VNC Websocket connections. If a bare websocket option is given, the Websocket port is 5700+display. An alternative port can be specified with the syntax "websocket"=port.

If host is specified connections will only be allowed from this host. It is possible to control the websocket listen address independently, using the syntax "websocket"=host:port.

If no TLS credentials are provided, the websocket connection runs in unencrypted mode. If TLS credentials are provided, the websocket connection requires encrypted client connections.

password

Require that password based authentication is used for client connections.

The password must be set separately using the "set_password" command in the pcsys_monitor. The syntax to change your password is: "set_password <protocol> <password>" where <protocol> could be either "vnc" or "spice".

If you would like to change <protocol> password expiration, you should use "expire_password <protocol> <expiration-time>" where expiration time could be one of the following options: now, never, +seconds or UNIX time of expiration, e.g. +60 to make password expire in 60 seconds, or 1335196800 to make password expire on "Mon Apr 23 12:00:00 EDT 2012" (UNIX time for this date and time).

You can also use keywords "now" or "never" for the expiration time to allow <protocol> password to expire immediately or never expire.

tls-creds=ID

Provides the ID of a set of TLS credentials to use to secure the VNC server. They will apply to both the normal VNC server socket and the websocket socket (if enabled). Setting TLS credentials will cause the VNC server socket to enable the VeNCrypt auth mechanism. The credentials should have been previously created using the -object tls-creds argument.

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 vnc_security section for details on using SASL authentication.

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 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.

lossy

Enable lossy compression methods (gradient, JPEG, ...). If this option is set, VNC client may receive lossy framebuffer updates depending on its encoding settings. Enabling this option can save a lot of bandwidth at the expense of quality.

non-adaptive

Disable adaptive encodings. Adaptive encodings are enabled by default. An adaptive encoding will try to detect frequently updated screen regions, and send updates in these regions using a lossy encoding (like JPEG). This can be really helpful to save bandwidth when playing videos. Disabling adaptive encodings restores the original static behavior of encodings like Tight.

share=[allow-exclusive|force-shared|ignore]

Set display sharing policy. 'allow-exclusive' allows clients to ask for exclusive access. As suggested by the rfb spec this is implemented by dropping other connections. Connecting multiple clients in parallel requires all clients asking for a shared session (vncviewer: -shared switch). This is the default. 'force-shared' disables exclusive client access. Useful for shared desktop sessions, where you don't want someone forgetting specify -shared disconnect everybody else. 'ignore' completely ignores the shared flag and allows everybody connect unconditionally. Doesn't conform to the rfb spec but is traditional QEMU behavior.

key-delay-ms

Set keyboard delay, for key down and key up events, in milliseconds. Default is 10. Keyboards are low-bandwidth devices, so this slowdown can help the device and guest to keep up and not lose events in case events are arriving in bulk. Possible causes for the latter are flaky network connections, or scripts for automated testing.

id=id

Assign symbolic name for use in monitor commands.

ipv4=on|off and ipv6=on|off

Specify that either IPv4 or IPv6 must be enabled. If neither is specified both protocols are enabled.

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 10.0.2.0/24.

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.

ipv6-net=addr[/int]

Set IPv6 network address the guest will see (default is fec0::/64). The network prefix is given in the usual hexadecimal IPv6 address notation. The prefix size is optional, and is given as the number of valid top-most bits (default is 64).

ipv6-host=addr

Specify the guest-visible IPv6 address of the host. Default is the 2nd IPv6 in the guest network, i.e. xxxx::2.

restrict=on|off

If this option 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 any explicitly set forwarding rules.

hostname=name

Specifies the client hostname reported by the built-in DHCP server.

dhcpstart=addr

Specify the first of the 16 IPs the built-in DHCP server can assign. Default is the 15th to 31st IP in the guest network, i.e. x.x.x.15 to x.x.x.31.

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.

ipv6-dns=addr

Specify the guest-visible address of the IPv6 virtual nameserver. The address must be different from the host address. Default is the 3rd IP in the guest network, i.e. xxxx::3.

dnssearch=domain

Provides an entry for the domain-search list sent by the built-in DHCP server. More than one domain suffix can be transmitted by specifying this option multiple times. If supported, this will cause the guest to automatically try to append the given domain suffix(es) in case a domain name can not be resolved.

Example:

        qemu-system-i386 -nic user,dnssearch=mgmt.example.org,dnssearch=example.org
    

domainname=domain

Specifies the client domain name reported by the built-in DHCP server.

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).

tftp-server-name=name

In BOOTP reply, broadcast name as the "TFTP server name" (RFC2132 option 66). This can be used to advise the guest to load boot files or configurations from a different server than the host address.

bootfile=file

When using the user mode network stack, broadcast file as the BOOTP filename. In conjunction with tftp, this can be used to network boot a guest from a local directory.

Example (using pxelinux):

        qemu-system-i386 -hda linux.img -boot n -device e1000,netdev=n1 \
        -netdev user,id=n1,tftp=/path/to/tftp/files,bootfile=/pxelinux.0
    

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.

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-system-i386 -nic 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-system-i386 -nic 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.

guestfwd=[tcp]:server:port-dev

guestfwd=[tcp]:server:port-cmd:command

Forward guest TCP connections to the IP address server on port port to the character device dev or to a program executed by cmd:command which gets spawned for each connection. This option can be given multiple times.

You can either use a chardev directly and have that one used throughout QEMU's lifetime, like in the following example:

        # open 10.10.1.1:4321 on bootup, connect 10.0.2.100:1234 to it whenever
        # the guest accesses it
        qemu-system-i386 -nic user,guestfwd=tcp:10.0.2.100:1234-tcp:10.10.1.1:4321
    

Or you can execute a command on every TCP connection established by the guest, so that QEMU behaves similar to an inetd process for that virtual server:

        # call "netcat 10.10.1.1 4321" on every TCP connection to 10.0.2.100:1234
        # and connect the TCP stream to its stdin/stdout
        qemu-system-i386 -nic  'user,id=n1,guestfwd=tcp:10.0.2.100:1234-cmd:netcat 10.10.1.1 4321'
    

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 ethN=mcast), see <http://user-mode-linux.sf.net>.

3.

Use fd=h to specify an already opened UDP multicast socket.

Example:

        # launch one QEMU instance
        qemu-system-i386 linux.img \
        -device e1000,netdev=n1,mac=52:54:00:12:34:56 \
        -netdev socket,id=n1,mcast=230.0.0.1:1234
        # launch another QEMU instance on same "bus"
        qemu-system-i386 linux.img \
        -device e1000,netdev=n2,mac=52:54:00:12:34:57 \
        -netdev socket,id=n2,mcast=230.0.0.1:1234
        # launch yet another QEMU instance on same "bus"
        qemu-system-i386 linux.img \
        -device e1000,netdev=n3,mac=52:54:00:12:34:58 \
        -netdev socket,id=n3,mcast=230.0.0.1:1234

Example (User Mode Linux compat.):

        # launch QEMU instance (note mcast address selected is UML's default)
        qemu-system-i386 linux.img \
        -device e1000,netdev=n1,mac=52:54:00:12:34:56 \
        -netdev socket,id=n1,mcast=239.192.168.1:1102
        # launch UML
        /path/to/linux ubd0=/path/to/root_fs eth0=mcast

Example (send packets from host's 1.2.3.4):

        qemu-system-i386 linux.img \
        -device e1000,netdev=n1,mac=52:54:00:12:34:56 \
        -netdev socket,id=n1,mcast=239.192.168.1:1102,localaddr=1.2.3.4

src=srcaddr

source address (mandatory)

dst=dstaddr

destination address (mandatory)

udp

select udp encapsulation (default is ip).

srcport=srcport

source udp port.

dstport=dstport

destination udp port.

ipv6

force v6, otherwise defaults to v4.

rxcookie=rxcookie

txcookie=txcookie

Cookies are a weak form of security in the l2tpv3 specification. Their function is mostly to prevent misconfiguration. By default they are 32 bit.

cookie64

Set cookie size to 64 bit instead of the default 32

counter=off

Force a 'cut-down' L2TPv3 with no counter as in draft-mkonstan-l2tpext-keyed-ipv6-tunnel-00

pincounter=on

Work around broken counter handling in peer. This may also help on networks which have packet reorder.

offset=offset

Add an extra offset between header and data

For example, to attach a VM running on host 4.3.2.1 via L2TPv3 to the bridge br-lan on the remote Linux host 1.2.3.4:

        # Setup tunnel on linux host using raw ip as encapsulation
        # on 1.2.3.4
        ip l2tp add tunnel remote 4.3.2.1 local 1.2.3.4 tunnel_id 1 peer_tunnel_id 1 \
        encap udp udp_sport 16384 udp_dport 16384
        ip l2tp add session tunnel_id 1 name vmtunnel0 session_id \
        0xFFFFFFFF peer_session_id 0xFFFFFFFF
        ifconfig vmtunnel0 mtu 1500
        ifconfig vmtunnel0 up
        brctl addif br-lan vmtunnel0
        
        
        # on 4.3.2.1
        # launch QEMU instance - if your network has reorder or is very lossy add ,pincounter
        
        qemu-system-i386 linux.img -device e1000,netdev=n1 \
        -netdev l2tpv3,id=n1,src=4.2.3.1,dst=1.2.3.4,udp,srcport=16384,dstport=16384,rxsession=0xffffffff,txsession=0xffffffff,counter

TCP options: port=port[,host=host][,to=to][,ipv4][,ipv6][,nodelay]

host for a listening socket specifies the local address to be bound. For a connecting socket species the remote host to connect to. host is optional for listening sockets. If not specified it defaults to 0.0.0.0.

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. port can be given as either a port number or a service name. port is required.

to is only relevant to listening sockets. If it is specified, and port cannot be bound, QEMU will attempt to bind to subsequent ports up to and including to until it succeeds. to must be specified as a port number.

ipv4 and ipv6 specify that either IPv4 or IPv6 must be used. If neither is specified the socket may use either protocol.

nodelay disables the Nagle algorithm.

unix options: path=path

path specifies the local path of the unix socket. path is required.

-bt hci,null

(default) The corresponding Bluetooth HCI assumes no internal logic and will not respond to any HCI commands or emit events.

-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.

-bt hci[,vlan=n]

Add a virtual, standard HCI that will participate in the Bluetooth scatternet n (default 0). Similarly to -net VLANs, devices inside a bluetooth network n can only communicate with other devices in the same network (scatternet).

keyboard

Virtual wireless keyboard implementing the HIDP bluetooth profile.

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
    

pty

[Linux only] Pseudo TTY (a new PTY is automatically allocated)

none

No device is allocated.

null

void device

chardev:id

Use a named character device defined with the "-chardev" option.

/dev/XXX

[Linux only] Use host tty, e.g. /dev/ttyS0. The host serial port parameters are set according to the emulated ones.

/dev/parportN

[Linux only, parallel port only] Use host parallel port N. Currently SPP and EPP parallel port features can be used.

file:filename

Write output to filename. No character can be read.

stdio

[Unix only] standard input/output

pipe:filename

name pipe filename

COMn

[Windows only] Use host serial port n

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 set up a netcat redirector to allow telnet on port 5555 to access the QEMU port.

tcp:[host]:port[,server][,nowait][,nodelay][,reconnect=seconds]

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. The "reconnect" option only applies if noserver is set, if the connection goes down it will attempt to reconnect at the given interval. 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.

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.

websocket:host:port,server[,nowait][,nodelay]

The WebSocket protocol is used instead of raw tcp socket. The port acts as a WebSocket server. Client mode is not supported.

unix:path[,server][,nowait][,reconnect=seconds]

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.

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. 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:

braille

Braille device. This will use BrlAPI to display the braille output on a real or fake device.

msmouse

Three button serial mouse. Configure the guest to use Microsoft protocol.

ib700

iBASE 700 is a very simple ISA watchdog with a single timer.

i6300esb

Intel 6300ESB I/O controller hub is a much more featureful PCI-based dual-timer watchdog.

diag288

A virtual watchdog for s390x backed by the diagnose 288 hypercall (currently KVM only).

"-watchdog i6300esb -watchdog-action pause"

"-watchdog ib700"

"-echr 0x14"

"-echr 20"

target="native|gdb|auto"

Defines where the semihosting calls will be addressed, to QEMU ("native") or to GDB ("gdb"). The default is "auto", which means "gdb" during debug sessions and "native" otherwise.

arg=str1,arg=str2,...

Allows the user to pass input arguments, and can be used multiple times to build up a list. The old-style "-kernel"/"-append" method of passing a command line is still supported for backward compatibility. If both the "--semihosting-config arg" and the "-kernel"/"-append" are specified, the former is passed to semihosting as it always takes precedence.

obsolete=string

Enable Obsolete system calls

elevateprivileges=string

Disable set*uid|gid system calls

spawn=string

Disable *fork and execve

resourcecontrol=string

Disable process affinity and schedular priority

[enable=]pattern

Immediately enable events matching pattern (either event name or a globbing pattern). This option is only available if QEMU has been compiled with the simple, log or ftrace tracing backend. To specify multiple events or patterns, specify the -trace option multiple times.

Use "-trace help" to print a list of names of trace points.

events=file

Immediately enable events listed in file. The file must contain one event name (as listed in the trace-events-all file) per line; globbing patterns are accepted too. This option is only available if QEMU has been compiled with the simple, log or ftrace tracing backend.

file=file

Log output traces to file. This option is only available if QEMU has been compiled with the simple tracing backend.

-object memory-backend-file,id=id,size=size,mem-path=dir,share=on|off,discard-data=on|off,merge=on|off,dump=on|off,prealloc=on|off,host-nodes=host-nodes,policy=default|preferred|bind|interleave,align=align

Creates a memory file backend object, which can be used to back the guest RAM with huge pages.

The id parameter is a unique ID that will be used to reference this memory region when configuring the -numa argument.

The size option provides the size of the memory region, and accepts common suffixes, eg 500M.

The mem-path provides the path to either a shared memory or huge page filesystem mount.

The share boolean option determines whether the memory region is marked as private to QEMU, or shared. The latter allows a co-operating external process to access the QEMU memory region.

The share is also required for pvrdma devices due to limitations in the RDMA API provided by Linux.

Setting share=on might affect the ability to configure NUMA bindings for the memory backend under some circumstances, see Documentation/vm/numa_memory_policy.txt on the Linux kernel source tree for additional details.

Setting the discard-data boolean option to on indicates that file contents can be destroyed when QEMU exits, to avoid unnecessarily flushing data to the backing file. Note that discard-data is only an optimization, and QEMU might not discard file contents if it aborts unexpectedly or is terminated using SIGKILL.

The merge boolean option enables memory merge, also known as MADV_MERGEABLE, so that Kernel Samepage Merging will consider the pages for memory deduplication.

Setting the dump boolean option to off excludes the memory from core dumps. This feature is also known as MADV_DONTDUMP.

The prealloc boolean option enables memory preallocation.

The host-nodes option binds the memory range to a list of NUMA host nodes.

The policy option sets the NUMA policy to one of the following values:

-object memory-backend-ram,id=id,merge=on|off,dump=on|off,share=on|off,prealloc=on|off,size=size,host-nodes=host-nodes,policy=default|preferred|bind|interleave

Creates a memory backend object, which can be used to back the guest RAM. Memory backend objects offer more control than the -m option that is traditionally used to define guest RAM. Please refer to memory-backend-file for a description of the options.

-object memory-backend-memfd,id=id,merge=on|off,dump=on|off,share=on|off,prealloc=on|off,size=size,host-nodes=host-nodes,policy=default|preferred|bind|interleave,seal=on|off,hugetlb=on|off,hugetlbsize=size

Creates an anonymous memory file backend object, which allows QEMU to share the memory with an external process (e.g. when using vhost-user). The memory is allocated with memfd and optional sealing. (Linux only)

The seal option creates a sealed-file, that will block further resizing the memory ('on' by default).

The hugetlb option specify the file to be created resides in the hugetlbfs filesystem (since Linux 4.14). Used in conjunction with the hugetlb option, the hugetlbsize option specify the hugetlb page size on systems that support multiple hugetlb page sizes (it must be a power of 2 value supported by the system).

In some versions of Linux, the hugetlb option is incompatible with the seal option (requires at least Linux 4.16).

Please refer to memory-backend-file for a description of the other options.

The share boolean option is on by default with memfd.

-object rng-random,id=id,filename=/dev/random

Creates a random number generator backend which obtains entropy from a device on the host. The id parameter is a unique ID that will be used to reference this entropy backend from the virtio-rng device. The filename parameter specifies which file to obtain entropy from and if omitted defaults to /dev/random.

-object rng-egd,id=id,chardev=chardevid

Creates a random number generator backend which obtains entropy from an external daemon running on the host. The id parameter is a unique ID that will be used to reference this entropy backend from the virtio-rng device. The chardev parameter is the unique ID of a character device backend that provides the connection to the RNG daemon.

-object tls-creds-anon,id=id,endpoint=endpoint,dir=/path/to/cred/dir,verify-peer=on|off

Creates a TLS anonymous credentials object, which can be used to provide TLS support on network backends. The id parameter is a unique ID which network backends will use to access the credentials. The endpoint is either server or client depending on whether the QEMU network backend that uses the credentials will be acting as a client or as a server. If verify-peer is enabled (the default) then once the handshake is completed, the peer credentials will be verified, though this is a no-op for anonymous credentials.

The dir parameter tells QEMU where to find the credential files. For server endpoints, this directory may contain a file dh-params.pem providing diffie-hellman parameters to use for the TLS server. If the file is missing, QEMU will generate a set of DH parameters at startup. This is a computationally expensive operation that consumes random pool entropy, so it is recommended that a persistent set of parameters be generated upfront and saved.

-object tls-creds-psk,id=id,endpoint=endpoint,dir=/path/to/keys/dir[,username=username]

Creates a TLS Pre-Shared Keys (PSK) credentials object, which can be used to provide TLS support on network backends. The id parameter is a unique ID which network backends will use to access the credentials. The endpoint is either server or client depending on whether the QEMU network backend that uses the credentials will be acting as a client or as a server. For clients only, username is the username which will be sent to the server. If omitted it defaults to "qemu".

The dir parameter tells QEMU where to find the keys file. It is called "dir/keys.psk" and contains "username:key" pairs. This file can most easily be created using the GnuTLS "psktool" program.

For server endpoints, dir may also contain a file dh-params.pem providing diffie-hellman parameters to use for the TLS server. If the file is missing, QEMU will generate a set of DH parameters at startup. This is a computationally expensive operation that consumes random pool entropy, so it is recommended that a persistent set of parameters be generated up front and saved.

-object tls-creds-x509,id=id,endpoint=endpoint,dir=/path/to/cred/dir,priority=priority,verify-peer=on|off,passwordid=id

Creates a TLS anonymous credentials object, which can be used to provide TLS support on network backends. The id parameter is a unique ID which network backends will use to access the credentials. The endpoint is either server or client depending on whether the QEMU network backend that uses the credentials will be acting as a client or as a server. If verify-peer is enabled (the default) then once the handshake is completed, the peer credentials will be verified. With x509 certificates, this implies that the clients must be provided with valid client certificates too.

The dir parameter tells QEMU where to find the credential files. For server endpoints, this directory may contain a file dh-params.pem providing diffie-hellman parameters to use for the TLS server. If the file is missing, QEMU will generate a set of DH parameters at startup. This is a computationally expensive operation that consumes random pool entropy, so it is recommended that a persistent set of parameters be generated upfront and saved.

For x509 certificate credentials the directory will contain further files providing the x509 certificates. The certificates must be stored in PEM format, in filenames ca-cert.pem, ca-crl.pem (optional), server-cert.pem (only servers), server-key.pem (only servers), client-cert.pem (only clients), and client-key.pem (only clients).

For the server-key.pem and client-key.pem files which contain sensitive private keys, it is possible to use an encrypted version by providing the passwordid parameter. This provides the ID of a previously created "secret" object containing the password for decryption.

The priority parameter allows to override the global default priority used by gnutls. This can be useful if the system administrator needs to use a weaker set of crypto priorities for QEMU without potentially forcing the weakness onto all applications. Or conversely if one wants wants a stronger default for QEMU than for all other applications, they can do this through this parameter. Its format is a gnutls priority string as described at <https://gnutls.org/manual/html_node/Priority-Strings.html>.

-object filter-buffer,id=id,netdev=netdevid,interval=t[,queue=all|rx|tx][,status=on|off]

Interval t can't be 0, this filter batches the packet delivery: all packets arriving in a given interval on netdev netdevid are delayed until the end of the interval. Interval is in microseconds. status is optional that indicate whether the netfilter is on (enabled) or off (disabled), the default status for netfilter will be 'on'.

queue all|rx|tx is an option that can be applied to any netfilter.

all: the filter is attached both to the receive and the transmit queue of the netdev (default).

rx: the filter is attached to the receive queue of the netdev, where it will receive packets sent to the netdev.

tx: the filter is attached to the transmit queue of the netdev, where it will receive packets sent by the netdev.

-object filter-mirror,id=id,netdev=netdevid,outdev=chardevid,queue=all|rx|tx[,vnet_hdr_support]

filter-mirror on netdev netdevid,mirror net packet to chardevchardevid, if it has the vnet_hdr_support flag, filter-mirror will mirror packet with vnet_hdr_len.

-object filter-redirector,id=id,netdev=netdevid,indev=chardevid,outdev=chardevid,queue=all|rx|tx[,vnet_hdr_support]

filter-redirector on netdev netdevid,redirect filter's net packet to chardev chardevid,and redirect indev's packet to filter.if it has the vnet_hdr_support flag, filter-redirector will redirect packet with vnet_hdr_len. Create a filter-redirector we need to differ outdev id from indev id, id can not be the same. we can just use indev or outdev, but at least one of indev or outdev need to be specified.

-object filter-rewriter,id=id,netdev=netdevid,queue=all|rx|tx,[vnet_hdr_support]

Filter-rewriter is a part of COLO project.It will rewrite tcp packet to secondary from primary to keep secondary tcp connection,and rewrite tcp packet to primary from secondary make tcp packet can be handled by client.if it has the vnet_hdr_support flag, we can parse packet with vnet header.

usage: colo secondary: -object filter-redirector,id=f1,netdev=hn0,queue=tx,indev=red0 -object filter-redirector,id=f2,netdev=hn0,queue=rx,outdev=red1 -object filter-rewriter,id=rew0,netdev=hn0,queue=all

-object filter-dump,id=id,netdev=dev[,file=filename][,maxlen=len]

Dump the network traffic on netdev dev to the file specified by filename. 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.

-object colo-compare,id=id,primary_in=chardevid,secondary_in=chardevid,outdev=chardevid[,vnet_hdr_support]

Colo-compare gets packet from primary_inchardevid and secondary_inchardevid, than compare primary packet with secondary packet. If the packets are same, we will output primary packet to outdevchardevid, else we will notify colo-frame do checkpoint and send primary packet to outdevchardevid. if it has the vnet_hdr_support flag, colo compare will send/recv packet with vnet_hdr_len.

we must use it with the help of filter-mirror and filter-redirector.

        primary:
        -netdev tap,id=hn0,vhost=off,script=/etc/qemu-ifup,downscript=/etc/qemu-ifdown
        -device e1000,id=e0,netdev=hn0,mac=52:a4:00:12:78:66
        -chardev socket,id=mirror0,host=3.3.3.3,port=9003,server,nowait
        -chardev socket,id=compare1,host=3.3.3.3,port=9004,server,nowait
        -chardev socket,id=compare0,host=3.3.3.3,port=9001,server,nowait
        -chardev socket,id=compare0-0,host=3.3.3.3,port=9001
        -chardev socket,id=compare_out,host=3.3.3.3,port=9005,server,nowait
        -chardev socket,id=compare_out0,host=3.3.3.3,port=9005
        -object filter-mirror,id=m0,netdev=hn0,queue=tx,outdev=mirror0
        -object filter-redirector,netdev=hn0,id=redire0,queue=rx,indev=compare_out
        -object filter-redirector,netdev=hn0,id=redire1,queue=rx,outdev=compare0
        -object colo-compare,id=comp0,primary_in=compare0-0,secondary_in=compare1,outdev=compare_out0
        
        secondary:
        -netdev tap,id=hn0,vhost=off,script=/etc/qemu-ifup,down script=/etc/qemu-ifdown
        -device e1000,netdev=hn0,mac=52:a4:00:12:78:66
        -chardev socket,id=red0,host=3.3.3.3,port=9003
        -chardev socket,id=red1,host=3.3.3.3,port=9004
        -object filter-redirector,id=f1,netdev=hn0,queue=tx,indev=red0
        -object filter-redirector,id=f2,netdev=hn0,queue=rx,outdev=red1
    

If you want to know the detail of above command line, you can read the colo-compare git log.

-object cryptodev-backend-builtin,id=id[,queues=queues]

Creates a cryptodev backend which executes crypto opreation from the QEMU cipher APIS. The id parameter is a unique ID that will be used to reference this cryptodev backend from the virtio-crypto device. The queues parameter is optional, which specify the queue number of cryptodev backend, the default of queues is 1.

        # qemu-system-x86_64 \
        [...] \
        -object cryptodev-backend-builtin,id=cryptodev0 \
        -device virtio-crypto-pci,id=crypto0,cryptodev=cryptodev0 \
        [...]
    

-object cryptodev-vhost-user,id=id,chardev=chardevid[,queues=queues]

Creates a vhost-user cryptodev backend, backed by a chardev chardevid. The id parameter is a unique ID that will be used to reference this cryptodev backend from the virtio-crypto device. The chardev should be a unix domain socket backed one. The vhost-user uses a specifically defined protocol to pass vhost ioctl replacement messages to an application on the other end of the socket. The queues parameter is optional, which specify the queue number of cryptodev backend for multiqueue vhost-user, the default of queues is 1.

        # qemu-system-x86_64 \
        [...] \
        -chardev socket,id=chardev0,path=/path/to/socket \
        -object cryptodev-vhost-user,id=cryptodev0,chardev=chardev0 \
        -device virtio-crypto-pci,id=crypto0,cryptodev=cryptodev0 \
        [...]
    

-object secret,id=id,data=string,format=raw|base64[,keyid=secretid,iv=string]

-object secret,id=id,file=filename,format=raw|base64[,keyid=secretid,iv=string]

Defines a secret to store a password, encryption key, or some other sensitive data. The sensitive data can either be passed directly via the data parameter, or indirectly via the file parameter. Using the data parameter is insecure unless the sensitive data is encrypted.

The sensitive data can be provided in raw format (the default), or base64. When encoded as JSON, the raw format only supports valid UTF-8 characters, so base64 is recommended for sending binary data. QEMU will convert from which ever format is provided to the format it needs internally. eg, an RBD password can be provided in raw format, even though it will be base64 encoded when passed onto the RBD sever.

For added protection, it is possible to encrypt the data associated with a secret using the AES-256-CBC cipher. Use of encryption is indicated by providing the keyid and iv parameters. The keyid parameter provides the ID of a previously defined secret that contains the AES-256 decryption key. This key should be 32-bytes long and be base64 encoded. The iv parameter provides the random initialization vector used for encryption of this particular secret and should be a base64 encrypted string of the 16-byte IV.

The simplest (insecure) usage is to provide the secret inline

        # $QEMU -object secret,id=sec0,data=letmein,format=raw
    

The simplest secure usage is to provide the secret via a file

# printf "letmein" > mypasswd.txt # $QEMU -object secret,id=sec0,file=mypasswd.txt,format=raw

For greater security, AES-256-CBC should be used. To illustrate usage, consider the openssl command line tool which can encrypt the data. Note that when encrypting, the plaintext must be padded to the cipher block size (32 bytes) using the standard PKCS#5/6 compatible padding algorithm.

First a master key needs to be created in base64 encoding:

        # openssl rand -base64 32 > key.b64
        # KEY=$(base64 -d key.b64 | hexdump  -v -e '/1 "%02X"')
    

Each secret to be encrypted needs to have a random initialization vector generated. These do not need to be kept secret

        # openssl rand -base64 16 > iv.b64
        # IV=$(base64 -d iv.b64 | hexdump  -v -e '/1 "%02X"')
    

The secret to be defined can now be encrypted, in this case we're telling openssl to base64 encode the result, but it could be left as raw bytes if desired.

        # SECRET=$(printf "letmein" |
        openssl enc -aes-256-cbc -a -K $KEY -iv $IV)
    

When launching QEMU, create a master secret pointing to "key.b64" and specify that to be used to decrypt the user password. Pass the contents of "iv.b64" to the second secret

        # $QEMU \
        -object secret,id=secmaster0,format=base64,file=key.b64 \
        -object secret,id=sec0,keyid=secmaster0,format=base64,\
        data=$SECRET,iv=$(<iv.b64)
    

-object sev-guest,id=id,cbitpos=cbitpos,reduced-phys-bits=val,[sev-device=string,policy=policy,handle=handle,dh-cert-file=file,session-file=file]

Create a Secure Encrypted Virtualization (SEV) guest object, which can be used to provide the guest memory encryption support on AMD processors.

When memory encryption is enabled, one of the physical address bit (aka the C-bit) is utilized to mark if a memory page is protected. The cbitpos is used to provide the C-bit position. The C-bit position is Host family dependent hence user must provide this value. On EPYC, the value should be 47.

When memory encryption is enabled, we loose certain bits in physical address space. The reduced-phys-bits is used to provide the number of bits we loose in physical address space. Similar to C-bit, the value is Host family dependent. On EPYC, the value should be 5.

The sev-device provides the device file to use for communicating with the SEV firmware running inside AMD Secure Processor. The default device is '/dev/sev'. If hardware supports memory encryption then /dev/sev devices are created by CCP driver.

The policy provides the guest policy to be enforced by the SEV firmware and restrict what configuration and operational commands can be performed on this guest by the hypervisor. The policy should be provided by the guest owner and is bound to the guest and cannot be changed throughout the lifetime of the guest. The default is 0.

If guest policy allows sharing the key with another SEV guest then handle can be use to provide handle of the guest from which to share the key.

The dh-cert-file and session-file provides the guest owner's Public Diffie-Hillman key defined in SEV spec. The PDH and session parameters are used for establishing a cryptographic session with the guest owner to negotiate keys used for attestation. The file must be encoded in base64.

e.g to launch a SEV guest

        # $QEMU \
        ......
        -object sev-guest,id=sev0,cbitpos=47,reduced-phys-bits=5 \
        -machine ...,memory-encryption=sev0
        .....
    

1

Target system display

2

Monitor

3

Serial port

protocol

'http', 'https', 'ftp', or 'ftps'.

username

Optional username for authentication to the remote server.

password

Optional password for authentication to the remote server.

host

Address of the remote server.

path

Path on the remote server, including any query string.

The following options are also supported:

url

The full URL when passing options to the driver explicitly.

readahead

The amount of data to read ahead with each range request to the remote server. This value may optionally have the suffix 'T', 'G', 'M', 'K', 'k' or 'b'. If it does not have a suffix, it will be assumed to be in bytes. The value must be a multiple of 512 bytes. It defaults to 256k.

sslverify

Whether to verify the remote server's certificate when connecting over SSL. It can have the value 'on' or 'off'. It defaults to 'on'.

cookie

Send this cookie (it can also be a list of cookies separated by ';') with each outgoing request. Only supported when using protocols such as HTTP which support cookies, otherwise ignored.

timeout

Set the timeout in seconds of the CURL connection. This timeout is the time that CURL waits for a response from the remote server to get the size of the image to be downloaded. If not set, the default timeout of 5 seconds is used.

Note that when passing options to qemu explicitly, driver is the value of <protocol>.

Example: boot from a remote Fedora 20 live ISO image

        qemu-system-x86_64 --drive media=cdrom,file=http://dl.fedoraproject.org/pub/fedora/linux/releases/20/Live/x86_64/Fedora-Live-Desktop-x86_64-20-1.iso,readonly
        
        qemu-system-x86_64 --drive media=cdrom,file.driver=http,file.url=http://dl.fedoraproject.org/pub/fedora/linux/releases/20/Live/x86_64/Fedora-Live-Desktop-x86_64-20-1.iso,readonly

Example: boot from a remote Fedora 20 cloud image using a local overlay for writes, copy-on-read, and a readahead of 64k

        qemu-img create -f qcow2 -o backing_file='json:{"file.driver":"http",, "file.url":"https://dl.fedoraproject.org/pub/fedora/linux/releases/20/Images/x86_64/Fedora-x86_64-20-20131211.1-sda.qcow2",, "file.readahead":"64k"}' /tmp/Fedora-x86_64-20-20131211.1-sda.qcow2
        
        qemu-system-x86_64 -drive file=/tmp/Fedora-x86_64-20-20131211.1-sda.qcow2,copy-on-read=on

Example: boot from an image stored on a VMware vSphere server with a self-signed certificate using a local overlay for writes, a readahead of 64k and a timeout of 10 seconds.

        qemu-img create -f qcow2 -o backing_file='json:{"file.driver":"https",, "file.url":"https://user:password@vsphere.example.com/folder/test/test-flat.vmdk?dcPath=Datacenter&dsName=datastore1",, "file.sslverify":"off",, "file.readahead":"64k",, "file.timeout":10}' /tmp/test.qcow2
        
        qemu-system-x86_64 -drive file=/tmp/test.qcow2