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qemu-doc: split qemu-doc.texi in multiple files

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In order to facilitate the reorganization of qemu-doc.texi content,
as well as the conversion to rST/Sphinx, split it in multiple .texi
files that are included from docs/system.

The "other devices" section is renamed to ivshmem and placed last.

Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Alex Bennée <alex.bennee@linaro.org>
Tested-by: Alex Bennée <alex.bennee@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Message-id: 20200228153619.9906-6-peter.maydell@linaro.org
Message-id: 20200226113034.6741-6-pbonzini@redhat.com
Reviewed-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
This commit is contained in:
Paolo Bonzini 2020-02-28 15:35:51 +00:00 committed by Peter Maydell
parent 5600d275d5
commit fdeccf932d
17 changed files with 1483 additions and 1454 deletions
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@ -1123,6 +1123,22 @@ qemu-doc.html qemu-doc.info qemu-doc.pdf qemu-doc.txt: \
qemu-tech.texi qemu-option-trace.texi \
qemu-deprecated.texi qemu-monitor.texi \
qemu-monitor-info.texi \
docs/system/quickstart.texi \
docs/system/invocation.texi \
docs/system/keys.texi \
docs/system/mux-chardev.texi \
docs/system/monitor.texi \
docs/system/cpu-models-x86.texi \
docs/system/images.texi \
docs/system/net.texi \
docs/system/usb.texi \
docs/system/ivshmem.texi \
docs/system/linuxboot.texi \
docs/system/vnc-security.texi \
docs/system/tls.texi \
docs/system/gdb.texi \
docs/system/build-platforms.texi \
docs/system/license.texi \
docs/system/cpu-models-x86.texi docs/system/cpu-models-mips.texi \
docs/security.texi

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@node Supported build platforms
@appendix Supported build platforms
QEMU aims to support building and executing on multiple host OS platforms.
This appendix outlines which platforms are the major build targets. These
platforms are used as the basis for deciding upon the minimum required
versions of 3rd party software QEMU depends on. The supported platforms
are the targets for automated testing performed by the project when patches
are submitted for review, and tested before and after merge.
If a platform is not listed here, it does not imply that QEMU won't work.
If an unlisted platform has comparable software versions to a listed platform,
there is every expectation that it will work. Bug reports are welcome for
problems encountered on unlisted platforms unless they are clearly older
vintage than what is described here.
Note that when considering software versions shipped in distros as support
targets, QEMU considers only the version number, and assumes the features in
that distro match the upstream release with the same version. In other words,
if a distro backports extra features to the software in their distro, QEMU
upstream code will not add explicit support for those backports, unless the
feature is auto-detectable in a manner that works for the upstream releases
too.
The Repology site @url{https://repology.org} is a useful resource to identify
currently shipped versions of software in various operating systems, though
it does not cover all distros listed below.
@section Linux OS
For distributions with frequent, short-lifetime releases, the project will
aim to support all versions that are not end of life by their respective
vendors. For the purposes of identifying supported software versions, the
project will look at Fedora, Ubuntu, and openSUSE distros. Other short-
lifetime distros will be assumed to ship similar software versions.
For distributions with long-lifetime releases, the project will aim to support
the most recent major version at all times. Support for the previous major
version will be dropped 2 years after the new major version is released,
or when it reaches ``end of life''. For the purposes of identifying
supported software versions, the project will look at RHEL, Debian,
Ubuntu LTS, and SLES distros. Other long-lifetime distros will be
assumed to ship similar software versions.
@section Windows
The project supports building with current versions of the MinGW toolchain,
hosted on Linux.
@section macOS
The project supports building with the two most recent versions of macOS, with
the current homebrew package set available.
@section FreeBSD
The project aims to support the all the versions which are not end of life.
@section NetBSD
The project aims to support the most recent major version at all times. Support
for the previous major version will be dropped 2 years after the new major
version is released.
@section OpenBSD
The project aims to support the all the versions which are not end of life.

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@node gdb_usage
@section 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:
@example
@value{qemu_system} -s -kernel bzImage -hda rootdisk.img -append "root=/dev/hda"
Connected to host network interface: tun0
Waiting gdb connection on port 1234
@end example
Then launch gdb on the 'vmlinux' executable:
@example
> gdb vmlinux
@end example
In gdb, connect to QEMU:
@example
(gdb) target remote localhost:1234
@end example
Then you can use gdb normally. For example, type 'c' to launch the kernel:
@example
(gdb) c
@end example
Here are some useful tips in order to use gdb on system code:
@enumerate
@item
Use @code{info reg} to display all the CPU registers.
@item
Use @code{x/10i $eip} to display the code at the PC position.
@item
Use @code{set architecture i8086} to dump 16 bit code. Then use
@code{x/10i $cs*16+$eip} to dump the code at the PC position.
@end enumerate
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 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:
@table @code
@item maintenance packet qqemu.sstepbits
This will display the MASK bits used to control the single stepping IE:
@example
(gdb) maintenance packet qqemu.sstepbits
sending: "qqemu.sstepbits"
received: "ENABLE=1,NOIRQ=2,NOTIMER=4"
@end example
@item maintenance packet qqemu.sstep
This will display the current value of the mask used when single stepping IE:
@example
(gdb) maintenance packet qqemu.sstep
sending: "qqemu.sstep"
received: "0x7"
@end example
@item 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:
@example
(gdb) maintenance packet Qqemu.sstep=0x5
sending: "qemu.sstep=0x5"
received: "OK"
@end example
@end table

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@node disk_images
@section Disk Images
QEMU supports many disk image formats, including growable disk images
(their size increase as non empty sectors are written), compressed and
encrypted disk images.
@menu
* disk_images_quickstart:: Quick start for disk image creation
* disk_images_snapshot_mode:: Snapshot mode
* vm_snapshots:: VM snapshots
@end menu
@node disk_images_quickstart
@subsection Quick start for disk image creation
You can create a disk image with the command:
@example
qemu-img create myimage.img mysize
@end example
where @var{myimage.img} is the disk image filename and @var{mysize} is its
size in kilobytes. You can add an @code{M} suffix to give the size in
megabytes and a @code{G} suffix for gigabytes.
@c When this document is converted to rst we should make this into
@c a proper linked reference to the qemu-img documentation again:
See the qemu-img invocation documentation for more information.
@node disk_images_snapshot_mode
@subsection 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 @file{/tmp}. You can however force the
write back to the raw disk images by using the @code{commit} monitor
command (or @key{C-a s} in the serial console).
@node vm_snapshots
@subsection 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 @code{qcow2} disk image
format. Normally this device is the first virtual hard drive.
Use the monitor command @code{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 @code{loadvm} to restore a VM snapshot and @code{delvm} to remove
a VM snapshot. @code{info snapshots} lists the available snapshots
with their associated information:
@example
(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
@end example
A VM snapshot is made of a VM state info (its size is shown in
@code{info snapshots}) and a snapshot of every writable disk image.
The VM state info is stored in the first @code{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 @code{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) @code{-snapshot} option
(@ref{disk_images_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:
@itemize
@item
They cannot cope with removable devices if they are removed or
inserted after a snapshot is done.
@item
A few device drivers still have incomplete snapshot support so their
state is not saved or restored properly (in particular USB).
@end itemize

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@node sec_invocation
@section Invocation
@example
@c man begin SYNOPSIS
@command{@value{qemu_system}} [@var{options}] [@var{disk_image}]
@c man end
@end example
@c man begin OPTIONS
@var{disk_image} is a raw hard disk image for IDE hard disk 0. Some
targets do not need a disk image.
@include qemu-options.texi
@c man end
@subsection Device URL Syntax
@c TODO merge this with section Disk Images
@c man begin NOTES
In addition to using normal file images for the emulated storage devices,
QEMU can also use networked resources such as iSCSI devices. These are
specified using a special URL syntax.
@table @option
@item iSCSI
iSCSI support allows QEMU to access iSCSI resources directly and use as
images for the guest storage. Both disk and cdrom images are supported.
Syntax for specifying iSCSI LUNs is
``iscsi://<target-ip>[:<port>]/<target-iqn>/<lun>''
By default qemu will use the iSCSI initiator-name
'iqn.2008-11.org.linux-kvm[:<name>]' but this can also be set from the command
line or a configuration file.
Since version Qemu 2.4 it is possible to specify a iSCSI request timeout to detect
stalled requests and force a reestablishment of the session. The timeout
is specified in seconds. The default is 0 which means no timeout. Libiscsi
1.15.0 or greater is required for this feature.
Example (without authentication):
@example
@value{qemu_system} -iscsi initiator-name=iqn.2001-04.com.example:my-initiator \
-cdrom iscsi://192.0.2.1/iqn.2001-04.com.example/2 \
-drive file=iscsi://192.0.2.1/iqn.2001-04.com.example/1
@end example
Example (CHAP username/password via URL):
@example
@value{qemu_system} -drive file=iscsi://user%password@@192.0.2.1/iqn.2001-04.com.example/1
@end example
Example (CHAP username/password via environment variables):
@example
LIBISCSI_CHAP_USERNAME="user" \
LIBISCSI_CHAP_PASSWORD="password" \
@value{qemu_system} -drive file=iscsi://192.0.2.1/iqn.2001-04.com.example/1
@end example
@item NBD
QEMU supports NBD (Network Block Devices) both using TCP protocol as well
as Unix Domain Sockets. With TCP, the default port is 10809.
Syntax for specifying a NBD device using TCP, in preferred URI form:
``nbd://<server-ip>[:<port>]/[<export>]''
Syntax for specifying a NBD device using Unix Domain Sockets; remember
that '?' is a shell glob character and may need quoting:
``nbd+unix:///[<export>]?socket=<domain-socket>''
Older syntax that is also recognized:
``nbd:<server-ip>:<port>[:exportname=<export>]''
Syntax for specifying a NBD device using Unix Domain Sockets
``nbd:unix:<domain-socket>[:exportname=<export>]''
Example for TCP
@example
@value{qemu_system} --drive file=nbd:192.0.2.1:30000
@end example
Example for Unix Domain Sockets
@example
@value{qemu_system} --drive file=nbd:unix:/tmp/nbd-socket
@end example
@item SSH
QEMU supports SSH (Secure Shell) access to remote disks.
Examples:
@example
@value{qemu_system} -drive file=ssh://user@@host/path/to/disk.img
@value{qemu_system} -drive file.driver=ssh,file.user=user,file.host=host,file.port=22,file.path=/path/to/disk.img
@end example
Currently authentication must be done using ssh-agent. Other
authentication methods may be supported in future.
@item Sheepdog
Sheepdog is a distributed storage system for QEMU.
QEMU supports using either local sheepdog devices or remote networked
devices.
Syntax for specifying a sheepdog device
@example
sheepdog[+tcp|+unix]://[host:port]/vdiname[?socket=path][#snapid|#tag]
@end example
Example
@example
@value{qemu_system} --drive file=sheepdog://192.0.2.1:30000/MyVirtualMachine
@end example
See also @url{https://sheepdog.github.io/sheepdog/}.
@item GlusterFS
GlusterFS is a user space distributed file system.
QEMU supports the use of GlusterFS volumes for hosting VM disk images using
TCP, Unix Domain Sockets and RDMA transport protocols.
Syntax for specifying a VM disk image on GlusterFS volume is
@example
URI:
gluster[+type]://[host[:port]]/volume/path[?socket=...][,debug=N][,logfile=...]
JSON:
'json:@{"driver":"qcow2","file":@{"driver":"gluster","volume":"testvol","path":"a.img","debug":N,"logfile":"...",
@ "server":[@{"type":"tcp","host":"...","port":"..."@},
@ @{"type":"unix","socket":"..."@}]@}@}'
@end example
Example
@example
URI:
@value{qemu_system} --drive file=gluster://192.0.2.1/testvol/a.img,
@ file.debug=9,file.logfile=/var/log/qemu-gluster.log
JSON:
@value{qemu_system} 'json:@{"driver":"qcow2",
@ "file":@{"driver":"gluster",
@ "volume":"testvol","path":"a.img",
@ "debug":9,"logfile":"/var/log/qemu-gluster.log",
@ "server":[@{"type":"tcp","host":"1.2.3.4","port":24007@},
@ @{"type":"unix","socket":"/var/run/glusterd.socket"@}]@}@}'
@value{qemu_system} -drive driver=qcow2,file.driver=gluster,file.volume=testvol,file.path=/path/a.img,
@ file.debug=9,file.logfile=/var/log/qemu-gluster.log,
@ file.server.0.type=tcp,file.server.0.host=1.2.3.4,file.server.0.port=24007,
@ file.server.1.type=unix,file.server.1.socket=/var/run/glusterd.socket
@end example
See also @url{http://www.gluster.org}.
@item HTTP/HTTPS/FTP/FTPS
QEMU supports read-only access to files accessed over http(s) and ftp(s).
Syntax using a single filename:
@example
<protocol>://[<username>[:<password>]@@]<host>/<path>
@end example
where:
@table @option
@item protocol
'http', 'https', 'ftp', or 'ftps'.
@item username
Optional username for authentication to the remote server.
@item password
Optional password for authentication to the remote server.
@item host
Address of the remote server.
@item path
Path on the remote server, including any query string.
@end table
The following options are also supported:
@table @option
@item url
The full URL when passing options to the driver explicitly.
@item 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.
@item 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'.
@item 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.
@item 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.
@end table
Note that when passing options to qemu explicitly, @option{driver} is the value
of <protocol>.
Example: boot from a remote Fedora 20 live ISO image
@example
@value{qemu_system_x86} --drive media=cdrom,file=https://archives.fedoraproject.org/pub/archive/fedora/linux/releases/20/Live/x86_64/Fedora-Live-Desktop-x86_64-20-1.iso,readonly
@value{qemu_system_x86} --drive media=cdrom,file.driver=http,file.url=http://archives.fedoraproject.org/pub/fedora/linux/releases/20/Live/x86_64/Fedora-Live-Desktop-x86_64-20-1.iso,readonly
@end example
Example: boot from a remote Fedora 20 cloud image using a local overlay for
writes, copy-on-read, and a readahead of 64k
@example
qemu-img create -f qcow2 -o backing_file='json:@{"file.driver":"http",, "file.url":"http://archives.fedoraproject.org/pub/archive/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
@value{qemu_system_x86} -drive file=/tmp/Fedora-x86_64-20-20131211.1-sda.qcow2,copy-on-read=on
@end example
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.
@example
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
@value{qemu_system_x86} -drive file=/tmp/test.qcow2
@end example
@end table
@c man end

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@node pcsys_ivshmem
@section Inter-VM Shared Memory device
On Linux hosts, a shared memory device is available. The basic syntax
is:
@example
@value{qemu_system_x86} -device ivshmem-plain,memdev=@var{hostmem}
@end example
where @var{hostmem} names a host memory backend. For a POSIX shared
memory backend, use something like
@example
-object memory-backend-file,size=1M,share,mem-path=/dev/shm/ivshmem,id=@var{hostmem}
@end example
If desired, interrupts can be sent between guest VMs accessing the same shared
memory region. Interrupt support requires using a shared memory server and
using a chardev socket to connect to it. The code for the shared memory server
is qemu.git/contrib/ivshmem-server. An example syntax when using the shared
memory server is:
@example
# First start the ivshmem server once and for all
ivshmem-server -p @var{pidfile} -S @var{path} -m @var{shm-name} -l @var{shm-size} -n @var{vectors}
# Then start your qemu instances with matching arguments
@value{qemu_system_x86} -device ivshmem-doorbell,vectors=@var{vectors},chardev=@var{id}
-chardev socket,path=@var{path},id=@var{id}
@end example
When using the server, the guest will be assigned a VM ID (>=0) that allows guests
using the same server to communicate via interrupts. Guests can read their
VM ID from a device register (see ivshmem-spec.txt).
@subsection Migration with ivshmem
With device property @option{master=on}, the guest will copy the shared
memory on migration to the destination host. With @option{master=off},
the guest will not be able to migrate with the device attached. In the
latter case, the device should be detached and then reattached after
migration using the PCI hotplug support.
At most one of the devices sharing the same memory can be master. The
master must complete migration before you plug back the other devices.
@subsection ivshmem and hugepages
Instead of specifying the <shm size> using POSIX shm, you may specify
a memory backend that has hugepage support:
@example
@value{qemu_system_x86} -object memory-backend-file,size=1G,mem-path=/dev/hugepages/my-shmem-file,share,id=mb1
-device ivshmem-plain,memdev=mb1
@end example
ivshmem-server also supports hugepages mount points with the
@option{-m} memory path argument.

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@node pcsys_keys
@section Keys in the graphical frontends
@c man begin OPTIONS
During the graphical emulation, you can use special key combinations to change
modes. The default key mappings are shown below, but if you use @code{-alt-grab}
then the modifier is Ctrl-Alt-Shift (instead of Ctrl-Alt) and if you use
@code{-ctrl-grab} then the modifier is the right Ctrl key (instead of Ctrl-Alt):
@table @key
@item Ctrl-Alt-f
@kindex Ctrl-Alt-f
Toggle full screen
@item Ctrl-Alt-+
@kindex Ctrl-Alt-+
Enlarge the screen
@item Ctrl-Alt--
@kindex Ctrl-Alt--
Shrink the screen
@item Ctrl-Alt-u
@kindex Ctrl-Alt-u
Restore the screen's un-scaled dimensions
@item Ctrl-Alt-n
@kindex Ctrl-Alt-n
Switch to virtual console 'n'. Standard console mappings are:
@table @emph
@item 1
Target system display
@item 2
Monitor
@item 3
Serial port
@end table
@item Ctrl-Alt
@kindex Ctrl-Alt
Toggle mouse and keyboard grab.
@end table
@kindex Ctrl-Up
@kindex Ctrl-Down
@kindex Ctrl-PageUp
@kindex Ctrl-PageDown
In the virtual consoles, you can use @key{Ctrl-Up}, @key{Ctrl-Down},
@key{Ctrl-PageUp} and @key{Ctrl-PageDown} to move in the back log.
@c man end

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@node License
@appendix License
QEMU is a trademark of Fabrice Bellard.
QEMU is released under the
@url{https://www.gnu.org/licenses/gpl-2.0.txt,GNU General Public License},
version 2. Parts of QEMU have specific licenses, see file
@url{https://git.qemu.org/?p=qemu.git;a=blob_plain;f=LICENSE,LICENSE}.

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@node direct_linux_boot
@section 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:
@example
@value{qemu_system} -kernel bzImage -hda rootdisk.img -append "root=/dev/hda"
@end example
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.
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:
@example
@value{qemu_system} -kernel bzImage -hda rootdisk.img \
-append "root=/dev/hda console=ttyS0" -nographic
@end example
Use @key{Ctrl-a c} to switch between the serial console and the
monitor (@pxref{pcsys_keys}).

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@node pcsys_monitor
@section QEMU Monitor
@cindex QEMU monitor
The QEMU monitor is used to give complex commands to the QEMU
emulator. You can use it to:
@itemize @minus
@item
Remove or insert removable media images
(such as CD-ROM or floppies).
@item
Freeze/unfreeze the Virtual Machine (VM) and save or restore its state
from a disk file.
@item Inspect the VM state without an external debugger.
@end itemize
@subsection Commands
The following commands are available:
@include qemu-monitor.texi
@include qemu-monitor-info.texi
@subsection 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 @emph{$}.

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@node mux_keys
@section Keys in the character backend multiplexer
@c man begin OPTIONS
During emulation, if you are using a character backend multiplexer
(which is the default if you are using @option{-nographic}) then
several commands are available via an escape sequence. These
key sequences all start with an escape character, which is @key{Ctrl-a}
by default, but can be changed with @option{-echr}. The list below assumes
you're using the default.
@table @key
@item Ctrl-a h
@kindex Ctrl-a h
Print this help
@item Ctrl-a x
@kindex Ctrl-a x
Exit emulator
@item Ctrl-a s
@kindex Ctrl-a s
Save disk data back to file (if -snapshot)
@item Ctrl-a t
@kindex Ctrl-a t
Toggle console timestamps
@item Ctrl-a b
@kindex Ctrl-a b
Send break (magic sysrq in Linux)
@item Ctrl-a c
@kindex Ctrl-a c
Rotate between the frontends connected to the multiplexer (usually
this switches between the monitor and the console)
@item Ctrl-a Ctrl-a
@kindex Ctrl-a Ctrl-a
Send the escape character to the frontend
@end table
@c man end
@ignore
@c man begin SEEALSO
The HTML documentation of QEMU for more precise information and Linux
user mode emulator invocation.
@c man end
@c man begin AUTHOR
Fabrice Bellard
@c man end
@end ignore

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@node pcsys_network
@section Network emulation
QEMU can simulate several network cards (e.g. PCI or ISA cards on the PC
target) and can connect them to a network backend on the host or an emulated
hub. The various host network backends can either be used to connect the NIC of
the guest to a real network (e.g. by using a TAP devices or the non-privileged
user mode network stack), or to other guest instances running in another QEMU
process (e.g. by using the socket host network backend).
@subsection 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 @code{tapN}), and you
can then configure it as if it was a real ethernet card.
@subsubsection Linux host
As an example, you can download the @file{linux-test-xxx.tar.gz}
archive and copy the script @file{qemu-ifup} in @file{/etc} and
configure properly @code{sudo} so that the command @code{ifconfig}
contained in @file{qemu-ifup} can be executed as root. You must verify
that your host kernel supports the TAP network interfaces: the
device @file{/dev/net/tun} must be present.
See @ref{sec_invocation} to have examples of command lines using the
TAP network interfaces.
@subsubsection 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 : @url{https://openvpn.net/}.
@subsection 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:
@example
guest (10.0.2.15) <------> Firewall/DHCP server <-----> Internet
| (10.0.2.2)
|
----> DNS server (10.0.2.3)
|
----> SMB server (10.0.2.4)
@end example
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 ICMP traffic in general does not work with user mode networking.
@code{ping}, aka. ICMP echo, to the local router (10.0.2.2) shall work,
however. If you're using QEMU on Linux >= 3.0, it can use unprivileged ICMP
ping sockets to allow @code{ping} to the Internet. The host admin has to set
the ping_group_range in order to grant access to those sockets. To allow ping
for GID 100 (usually users group):
@example
echo 100 100 > /proc/sys/net/ipv4/ping_group_range
@end example
When using the built-in TFTP server, the router is also the TFTP
server.
When using the @option{'-netdev user,hostfwd=...'} 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.
@subsection Hubs
QEMU can simulate several hubs. A hub can be thought of 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). You can connect
guest NICs or host network backends to such a hub using the @option{-netdev
hubport} or @option{-nic hubport} options. The legacy @option{-net} option
also connects the given device to the emulated hub with ID 0 (i.e. the default
hub) unless you specify a netdev with @option{-net nic,netdev=xxx} here.
@subsection Connecting emulated networks between QEMU instances
Using the @option{-netdev socket} (or @option{-nic socket} or
@option{-net socket}) option, it is possible to create emulated
networks that span several QEMU instances.
See the description of the @option{-netdev socket} option in the
@ref{sec_invocation,,Invocation chapter} to have a basic example.

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@node pcsys_quickstart
@section Quick Start
@cindex quick start
Download and uncompress a hard disk image with Linux installed (e.g.
@file{linux.img}) and type:
@example
@value{qemu_system} linux.img
@end example
Linux should boot and give you a prompt.

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@node network_tls
@section TLS setup for network services
Almost all network services in QEMU have the ability to use TLS for
session data encryption, along with x509 certificates for simple
client authentication. What follows is a description of how to
generate certificates suitable for usage with QEMU, and applies to
the VNC server, character devices with the TCP backend, NBD server
and client, and migration server and client.
At a high level, QEMU requires certificates and private keys to be
provided in PEM format. Aside from the core fields, the certificates
should include various extension data sets, including v3 basic
constraints data, key purpose, key usage and subject alt name.
The GnuTLS package includes a command called @code{certtool} which can
be used to easily generate certificates and keys in the required format
with expected data present. Alternatively a certificate management
service may be used.
At a minimum it is necessary to setup a certificate authority, and
issue certificates to each server. If using x509 certificates for
authentication, then each client will also need to be issued a
certificate.
Assuming that the QEMU network services will only ever be exposed to
clients on a private intranet, there is no need to use a commercial
certificate authority to create certificates. A self-signed CA is
sufficient, and in fact likely to be more secure since it removes
the ability of malicious 3rd parties to trick the CA into mis-issuing
certs for impersonating your services. The only likely exception
where a commercial CA might be desirable is if enabling the VNC
websockets server and exposing it directly to remote browser clients.
In such a case it might be useful to use a commercial CA to avoid
needing to install custom CA certs in the web browsers.
The recommendation is for the server to keep its certificates in either
@code{/etc/pki/qemu} or for unprivileged users in @code{$HOME/.pki/qemu}.
@menu
* tls_generate_ca::
* tls_generate_server::
* tls_generate_client::
* tls_creds_setup::
* tls_psk::
@end menu
@node tls_generate_ca
@subsection 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.
@example
# certtool --generate-privkey > ca-key.pem
@end example
To generate a self-signed certificate requires one core piece of information,
the name of the organization. A template file @code{ca.info} should be
populated with the desired data to avoid having to deal with interactive
prompts from certtool:
@example
# 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
@end example
The @code{ca} keyword in the template sets the v3 basic constraints extension
to indicate this certificate is for a CA, while @code{cert_signing_key} sets
the key usage extension to indicate this will be used for signing other keys.
The generated @code{ca-cert.pem} file should be copied to all servers and
clients wishing to utilize TLS support in the VNC server. The @code{ca-key.pem}
must not be disclosed/copied anywhere except the host responsible for issuing
certificates.
@node tls_generate_server
@subsection 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 pieces of information for a server certificate are the hostnames and/or IP
addresses that will be used by clients when connecting. The hostname / IP address
that the client specifies when connecting will be validated against the hostname(s)
and IP address(es) recorded in the server certificate, and if no match is found
the client will close the connection.
Thus it is recommended that the server certificate include both the fully qualified
and unqualified hostnames. If the server will have permanently assigned IP address(es),
and clients are likely to use them when connecting, they may also be included in the
certificate. Both IPv4 and IPv6 addresses are supported. Historically certificates
only included 1 hostname in the @code{CN} field, however, usage of this field for
validation is now deprecated. Instead modern TLS clients will validate against the
Subject Alt Name extension data, which allows for multiple entries. In the future
usage of the @code{CN} field may be discontinued entirely, so providing SAN
extension data is strongly recommended.
On the host holding the CA, create template files containing the information
for each server, and use it to issue server certificates.
@example
# cat > server-hostNNN.info <<EOF
organization = Name of your organization
cn = hostNNN.foo.example.com
dns_name = hostNNN
dns_name = hostNNN.foo.example.com
ip_address = 10.0.1.87
ip_address = 192.8.0.92
ip_address = 2620:0:cafe::87
ip_address = 2001:24::92
tls_www_server
encryption_key
signing_key
EOF
# certtool --generate-privkey > server-hostNNN-key.pem
# certtool --generate-certificate \
--load-ca-certificate ca-cert.pem \
--load-ca-privkey ca-key.pem \
--load-privkey server-hostNNN-key.pem \
--template server-hostNNN.info \
--outfile server-hostNNN-cert.pem
@end example
The @code{dns_name} and @code{ip_address} fields in the template are setting
the subject alt name extension data. The @code{tls_www_server} keyword is the
key purpose extension to indicate this certificate is intended for usage in
a web server. Although QEMU network services are not in fact HTTP servers
(except for VNC websockets), setting this key purpose is still recommended.
The @code{encryption_key} and @code{signing_key} keyword is the key usage
extension to indicate this certificate is intended for usage in the data
session.
The @code{server-hostNNN-key.pem} and @code{server-hostNNN-cert.pem} files
should now be securely copied to the server for which they were generated,
and renamed to @code{server-key.pem} and @code{server-cert.pem} when added
to the @code{/etc/pki/qemu} directory on the target host. The @code{server-key.pem}
file is security sensitive and should be kept protected with file mode 0600
to prevent disclosure.
@node tls_generate_client
@subsection Issuing client certificates
The QEMU x509 TLS credential setup defaults to enabling client verification
using certificates, providing a simple authentication mechanism. If this
default is used, each client also needs to be issued a certificate. The client
certificate contains enough metadata to uniquely identify the client with the
scope of the certificate authority. The client certificate would typically
include fields for organization, state, city, building, etc.
Once again on the host holding the CA, create template files containing the
information for each client, and use it to issue client certificates.
@example
# cat > client-hostNNN.info <<EOF
country = GB
state = London
locality = City Of London
organization = Name of your organization
cn = hostNNN.foo.example.com
tls_www_client
encryption_key
signing_key
EOF
# certtool --generate-privkey > client-hostNNN-key.pem
# certtool --generate-certificate \
--load-ca-certificate ca-cert.pem \
--load-ca-privkey ca-key.pem \
--load-privkey client-hostNNN-key.pem \
--template client-hostNNN.info \
--outfile client-hostNNN-cert.pem
@end example
The subject alt name extension data is not required for clients, so the
the @code{dns_name} and @code{ip_address} fields are not included.
The @code{tls_www_client} keyword is the key purpose extension to indicate
this certificate is intended for usage in a web client. Although QEMU
network clients are not in fact HTTP clients, setting this key purpose is
still recommended. The @code{encryption_key} and @code{signing_key} keyword
is the key usage extension to indicate this certificate is intended for
usage in the data session.
The @code{client-hostNNN-key.pem} and @code{client-hostNNN-cert.pem} files
should now be securely copied to the client for which they were generated,
and renamed to @code{client-key.pem} and @code{client-cert.pem} when added
to the @code{/etc/pki/qemu} directory on the target host. The @code{client-key.pem}
file is security sensitive and should be kept protected with file mode 0600
to prevent disclosure.
If a single host is going to be using TLS in both a client and server
role, it is possible to create a single certificate to cover both roles.
This would be quite common for the migration and NBD services, where a
QEMU process will be started by accepting a TLS protected incoming migration,
and later itself be migrated out to another host. To generate a single
certificate, simply include the template data from both the client and server
instructions in one.
@example
# cat > both-hostNNN.info <<EOF
country = GB
state = London
locality = City Of London
organization = Name of your organization
cn = hostNNN.foo.example.com
dns_name = hostNNN
dns_name = hostNNN.foo.example.com
ip_address = 10.0.1.87
ip_address = 192.8.0.92
ip_address = 2620:0:cafe::87
ip_address = 2001:24::92
tls_www_server
tls_www_client
encryption_key
signing_key
EOF
# certtool --generate-privkey > both-hostNNN-key.pem
# certtool --generate-certificate \
--load-ca-certificate ca-cert.pem \
--load-ca-privkey ca-key.pem \
--load-privkey both-hostNNN-key.pem \
--template both-hostNNN.info \
--outfile both-hostNNN-cert.pem
@end example
When copying the PEM files to the target host, save them twice,
once as @code{server-cert.pem} and @code{server-key.pem}, and
again as @code{client-cert.pem} and @code{client-key.pem}.
@node tls_creds_setup
@subsection TLS x509 credential configuration
QEMU has a standard mechanism for loading x509 credentials that will be
used for network services and clients. It requires specifying the
@code{tls-creds-x509} class name to the @code{--object} command line
argument for the system emulators. Each set of credentials loaded should
be given a unique string identifier via the @code{id} parameter. A single
set of TLS credentials can be used for multiple network backends, so VNC,
migration, NBD, character devices can all share the same credentials. Note,
however, that credentials for use in a client endpoint must be loaded
separately from those used in a server endpoint.
When specifying the object, the @code{dir} parameters specifies which
directory contains the credential files. This directory is expected to
contain files with the names mentioned previously, @code{ca-cert.pem},
@code{server-key.pem}, @code{server-cert.pem}, @code{client-key.pem}
and @code{client-cert.pem} as appropriate. It is also possible to
include a set of pre-generated Diffie-Hellman (DH) parameters in a file
@code{dh-params.pem}, which can be created using the
@code{certtool --generate-dh-params} command. If omitted, QEMU will
dynamically generate DH parameters when loading the credentials.
The @code{endpoint} parameter indicates whether the credentials will
be used for a network client or server, and determines which PEM
files are loaded.
The @code{verify} parameter determines whether x509 certificate
validation should be performed. This defaults to enabled, meaning
clients will always validate the server hostname against the
certificate subject alt name fields and/or CN field. It also
means that servers will request that clients provide a certificate
and validate them. Verification should never be turned off for
client endpoints, however, it may be turned off for server endpoints
if an alternative mechanism is used to authenticate clients. For
example, the VNC server can use SASL to authenticate clients
instead.
To load server credentials with client certificate validation
enabled
@example
@value{qemu_system} -object tls-creds-x509,id=tls0,dir=/etc/pki/qemu,endpoint=server
@end example
while to load client credentials use
@example
@value{qemu_system} -object tls-creds-x509,id=tls0,dir=/etc/pki/qemu,endpoint=client
@end example
Network services which support TLS will all have a @code{tls-creds}
parameter which expects the ID of the TLS credentials object. For
example with VNC:
@example
@value{qemu_system} -vnc 0.0.0.0:0,tls-creds=tls0
@end example
@node tls_psk
@subsection TLS Pre-Shared Keys (PSK)
Instead of using certificates, you may also use TLS Pre-Shared Keys
(TLS-PSK). This can be simpler to set up than certificates but is
less scalable.
Use the GnuTLS @code{psktool} program to generate a @code{keys.psk}
file containing one or more usernames and random keys:
@example
mkdir -m 0700 /tmp/keys
psktool -u rich -p /tmp/keys/keys.psk
@end example
TLS-enabled servers such as qemu-nbd can use this directory like so:
@example
qemu-nbd \
-t -x / \
--object tls-creds-psk,id=tls0,endpoint=server,dir=/tmp/keys \
--tls-creds tls0 \
image.qcow2
@end example
When connecting from a qemu-based client you must specify the
directory containing @code{keys.psk} and an optional @var{username}
(defaults to ``qemu''):
@example
qemu-img info \
--object tls-creds-psk,id=tls0,dir=/tmp/keys,username=rich,endpoint=client \
--image-opts \
file.driver=nbd,file.host=localhost,file.port=10809,file.tls-creds=tls0,file.export=/
@end example

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@node pcsys_usb
@section USB emulation
QEMU can emulate a PCI UHCI, OHCI, EHCI or XHCI USB controller. You can
plug virtual USB devices or real host USB devices (only works with certain
host operating systems). QEMU will automatically create and connect virtual
USB hubs as necessary to connect multiple USB devices.
@menu
* usb_devices::
* host_usb_devices::
@end menu
@node usb_devices
@subsection Connecting USB devices
USB devices can be connected with the @option{-device usb-...} command line
option or the @code{device_add} monitor command. Available devices are:
@table @code
@item usb-mouse
Virtual Mouse. This will override the PS/2 mouse emulation when activated.
@item usb-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.
@item usb-storage,drive=@var{drive_id}
Mass storage device backed by @var{drive_id} (@pxref{disk_images})
@item usb-uas
USB attached SCSI device, see
@url{https://git.qemu.org/?p=qemu.git;a=blob_plain;f=docs/usb-storage.txt,usb-storage.txt}
for details
@item usb-bot
Bulk-only transport storage device, see
@url{https://git.qemu.org/?p=qemu.git;a=blob_plain;f=docs/usb-storage.txt,usb-storage.txt}
for details here, too
@item usb-mtp,rootdir=@var{dir}
Media transfer protocol device, using @var{dir} as root of the file tree
that is presented to the guest.
@item usb-host,hostbus=@var{bus},hostaddr=@var{addr}
Pass through the host device identified by @var{bus} and @var{addr}
@item usb-host,vendorid=@var{vendor},productid=@var{product}
Pass through the host device identified by @var{vendor} and @var{product} ID
@item usb-wacom-tablet
Virtual Wacom PenPartner tablet. This device is similar to the @code{tablet}
above but it can be used with the tslib library because in addition to touch
coordinates it reports touch pressure.
@item usb-kbd
Standard USB keyboard. Will override the PS/2 keyboard (if present).
@item usb-serial,chardev=@var{id}
Serial converter. This emulates an FTDI FT232BM chip connected to host character
device @var{id}.
@item usb-braille,chardev=@var{id}
Braille device. This will use BrlAPI to display the braille output on a real
or fake device referenced by @var{id}.
@item usb-net[,netdev=@var{id}]
Network adapter that supports CDC ethernet and RNDIS protocols. @var{id}
specifies a netdev defined with @code{-netdev @dots{},id=@var{id}}.
For instance, user-mode networking can be used with
@example
@value{qemu_system} [...] -netdev user,id=net0 -device usb-net,netdev=net0
@end example
@item usb-ccid
Smartcard reader device
@item usb-audio
USB audio device
@end table
@node host_usb_devices
@subsection 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.
@enumerate
@item 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 @file{mydriver.o}
to @file{mydriver.o.disabled}.
@item Verify that @file{/proc/bus/usb} is working (most Linux distributions should enable it by default). You should see something like that:
@example
ls /proc/bus/usb
001 devices drivers
@end example
@item 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:
@example
chown -R myuid /proc/bus/usb
@end example
@item Launch QEMU and do in the monitor:
@example
info usbhost
Device 1.2, speed 480 Mb/s
Class 00: USB device 1234:5678, USB DISK
@end example
You should see the list of the devices you can use (Never try to use
hubs, it won't work).
@item Add the device in QEMU by using:
@example
device_add usb-host,vendorid=0x1234,productid=0x5678
@end example
Normally the guest OS should report that a new USB device is plugged.
You can use the option @option{-device usb-host,...} to do the same.
@item Now you can try to use the host USB device in QEMU.
@end enumerate
When relaunching QEMU, you may have to unplug and plug again the USB
device to make it work again (this is a bug).

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@node vnc_security
@section 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.
@menu
* vnc_sec_none::
* vnc_sec_password::
* vnc_sec_certificate::
* vnc_sec_certificate_verify::
* vnc_sec_certificate_pw::
* vnc_sec_sasl::
* vnc_sec_certificate_sasl::
* vnc_setup_sasl::
@end menu
@node vnc_sec_none
@subsection 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
@example
@value{qemu_system} [...OPTIONS...] -vnc unix:/home/joebloggs/.qemu-myvm-vnc
@end example
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.
@node vnc_sec_password
@subsection 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 not supported when operating
in FIPS 140-2 compliance mode as it requires the use of the DES cipher. Password
authentication is requested with the @code{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.
@example
@value{qemu_system} [...OPTIONS...] -vnc :1,password -monitor stdio
(qemu) change vnc password
Password: ********
(qemu)
@end example
@node vnc_sec_certificate
@subsection 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.
@example
@value{qemu_system} [...OPTIONS...] \
-object tls-creds-x509,id=tls0,dir=/etc/pki/qemu,endpoint=server,verify-peer=no \
-vnc :1,tls-creds=tls0 -monitor stdio
@end example
In the above example @code{/etc/pki/qemu} should contain at least three files,
@code{ca-cert.pem}, @code{server-cert.pem} and @code{server-key.pem}. Unprivileged
users will want to use a private directory, for example @code{$HOME/.pki/qemu}.
NB the @code{server-key.pem} file should be protected with file mode 0600 to
only be readable by the user owning it.
@node vnc_sec_certificate_verify
@subsection 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. It uses the
same syntax as previously, but with @code{verify-peer} set to @code{yes}
instead.
@example
@value{qemu_system} [...OPTIONS...] \
-object tls-creds-x509,id=tls0,dir=/etc/pki/qemu,endpoint=server,verify-peer=yes \
-vnc :1,tls-creds=tls0 -monitor stdio
@end example
@node vnc_sec_certificate_pw
@subsection 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.
@example
@value{qemu_system} [...OPTIONS...] \
-object tls-creds-x509,id=tls0,dir=/etc/pki/qemu,endpoint=server,verify-peer=yes \
-vnc :1,tls-creds=tls0,password -monitor stdio
(qemu) change vnc password
Password: ********
(qemu)
@end example
@node vnc_sec_sasl
@subsection 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:
@example
@value{qemu_system} [...OPTIONS...] -vnc :1,sasl -monitor stdio
@end example
@node vnc_sec_certificate_sasl
@subsection 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:
@example
@value{qemu_system} [...OPTIONS...] \
-object tls-creds-x509,id=tls0,dir=/etc/pki/qemu,endpoint=server,verify-peer=yes \
-vnc :1,tls-creds=tls0,sasl -monitor stdio
@end example
@node vnc_setup_sasl
@subsection Configuring SASL mechanisms
The following documentation assumes use of the Cyrus SASL implementation on a
Linux host, but the principles should apply to any other SASL implementation
or host. 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 file.
If the TLS option is enabled for VNC, then it will provide session encryption,
otherwise the SASL mechanism will have to provide encryption. In the latter
case the list of possible plugins that can be used is drastically reduced. In
fact only the GSSAPI SASL mechanism provides an acceptable level of security
by modern standards. Previous versions of QEMU referred to the DIGEST-MD5
mechanism, however, it has multiple serious flaws described in detail in
RFC 6331 and thus should never be used any more. The SCRAM-SHA-1 mechanism
provides a simple username/password auth facility similar to DIGEST-MD5, but
does not support session encryption, so can only be used in combination with
TLS.
When not using TLS the recommended configuration is
@example
mech_list: gssapi
keytab: /etc/qemu/krb5.tab
@end example
This says to use the 'GSSAPI' mechanism with the Kerberos v5 protocol, with
the server principal stored in /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 Kerberos Realm.
When using TLS, if username+password authentication is desired, then a
reasonable configuration is
@example
mech_list: scram-sha-1
sasldb_path: /etc/qemu/passwd.db
@end example
The @code{saslpasswd2} program can be used to populate the @code{passwd.db}
file with accounts.
Other SASL configurations will be left as an exercise for the reader. Note that
all mechanisms, except GSSAPI, should be combined with use of TLS to ensure a
secure data channel.

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