Qemu on Linux

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Techniques: Qemu on Linux

This article is about setting up and running the Qemu emulator on Linux.

Notes

When Bochs mysteriously stopped being able to run Win98, I found that Qemu was able to use the exact same .img file Bochs had been using, and it did manage to load Win98 quite easily. It would appear, then, that the setup for Qemu on Linux is probably quite similar to that of Bochs.

Current issue: "warning: could not open /dev/net/tun: no virtual network emulation"

Manpage Documentation

NAME

qemu - QEMU System Emulator

SYNOPSIS

usage: qemu [options] [disk_image]

DESCRIPTION

The QEMU System emulator simulates a complete PC.

In order to meet specific user needs, two versions of QEMU are available:

1. "qemu-fast" uses the host Memory Management Unit (MMU) to simulate the x86 MMU. It is fast but has limitations because the whole 4 GB address space cannot be used and some memory mapped peripherials cannot be emulated accurately yet. Therefore, a specific guest Linux kernel can be used.

   Moreover there is no separation between the host and target address spaces, so it offers no security (the target OS can modify the "qemu-fast" code by writing at the right addresses).

2. "qemu" uses a software MMU. It is about two times slower but gives a more accurate emulation and a complete separation between the host and target address spaces.

QEMU emulates the following PC peripherials:

• i440FX host PCI bridge and PIIX3 PCI to ISA bridge
• Cirrus CLGD 5446 PCI VGA card or dummy VGA card with Bochs VESA extensions (hardware level, including all non-standard modes).
• PS/2 mouse and keyboard
• 2 PCI IDE interfaces with hard disk and CD-ROM support
• Floppy disk
• NE2000 PCI network adapters
• Serial ports
• Soundblaster 16 card

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

OPTIONS

• disk_image is a raw hard disk image for IDE hard disk 0.

General options

• -fda file
• -fdb file

Use file as floppy disk 0/1 image You can use the host floppy by using /dev/fd0 as filename.

• -hda file
• -hdb file
• -hdc file
• -hdd file

Use file as hard disk 0, 1, 2 or 3 image

• -cdrom file

Use file as CD-ROM image (you cannot use -hdc and and -cdrom at the same time). You can use the host CD-ROM by using /dev/cdrom as filename.

• -boot [a|c|d]

Boot on floppy (a), hard disk (c) or CD-ROM (d). Hard disk boot is the default.

• -snapshot

Write to temporary files instead of disk image files. In this case, the raw disk image you use is not written back. You can however force the write back by pressing C-a s

• -m megs

Set virtual RAM size to megs megabytes. Default is 128 MB.

• -nographic

Normally, QEMU uses SDL to display the VGA output. With this option, you can totally disable graphical output so that QEMU is a simple command line application. The emulated serial port is redirected on the console. Therefore, you can still use QEMU to debug a Linux kernel with a serial console.

• -enable-audio

The SB16 emulation is disabled by default as it may give problems with Windows. You can enable it manually with this option.

• -localtime

Set the real time clock to local time (the default is to UTC time). This option is needed to have correct date in MS-DOS or Windows.

• -full-screen

Start in full screen.

Network options

• -n script

Set TUN/TAP network init script [default=/etc/qemu-ifup]. This script is launched to configure the host network interface (usually tun0) corresponding to the virtual NE2000 card.

• -macaddr addr

Set the mac address of the first interface (the format is aa:bb:cc:dd:ee:ff in hexa). The mac address is incremented for each new network interface.

• -tun-fd fd

Assumes fd talks to a tap/tun host network interface and use it. Read <http://bellard.org/qemu/tetrinet.html> to have an example of its use.

• -user-net

Use the user mode network stack. This is the default if no tun/tap network init script is found.

• -tftp prefix

When using the user mode network stack, activate a built-in TFTP server. All filenames beginning with prefix can be downloaded from the host to the guest using a TFTP client. The TFTP client on the guest must be configured in binary mode (use the command "bin" of the Unix TFTP client). The host IP address on the guest is as usual 10.0.2.2.

• -smb dir

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.

In the guest Windows OS, the line:

10.0.2.4 smbserver

must be added in the file C:\WINDOWS\LMHOSTS (for windows 9x/Me) or C:\WINNT\SYSTEM32\DRIVERS\ETC\LMHOSTS (Windows NT/2000). Then dir can be accessed in \\smbserver\qemu.

Note that a SAMBA server must be installed on the host OS in /usr/sbin/smbd. QEMU was tested succesfully with smbd version 2.2.7a from the Red Hat 9.

• -redir [tcp|udp]:host-port:[guest-host]:guest-port

When using the user mode network stack, redirect incoming TCP or UDP connections to the host port host-port to the guest guest-host on guest port guest-port. If guest-host is not specified, its value is 10.0.2.15 (default address given by the built-in DHCP server).

For example, to redirect host X11 connection from screen 1 to guest screen 0, use the following:

# on the host
qemu -redir tcp: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 -redir tcp:5555::23 [...]
telnet localhost 5555

Then when you use on the host "telnet localhost 5555", you connect to the guest telnet server.

• -dummy-net

Use the dummy network stack: no packet will be received by the network cards.

Linux boot specific

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

• -kernel bzImage

Use bzImage as kernel image.

• -append cmdline

Use cmdline as kernel command line

• -initrd file

Use file as initial ram disk.

Debug/Expert options

• -serial dev

Redirect the virtual serial port to host device dev. Available devices are:

• • "vc"

    Virtual console

  • "pty"

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

  • "null"

    void device

  • "stdio"

    [Unix only] standard input/output

The default device is "vc" in graphical mode and "stdio" in non graphical mode.

This option can be used several times to simulate up to 4 serials ports.

• -monitor dev

Redirect the monitor to host device dev (same devices as the serial port). The default device is "vc" in graphical mode and "stdio" in non graphical mode.

• -s

Wait gdb connection to port 1234

• -p port

Change gdb connection port.

• -S

Do not start CPU at startup (you must type 'c' in the monitor).

• -d

Output log in /tmp/qemu.log

• -isa

Simulate an ISA-only system (default is PCI system).

• -std-vga

Simulate a standard VGA card with Bochs VBE extensions (default is Cirrus Logic GD5446 PCI VGA)

• -loadvm file

Start right away with a saved state ("loadvm" in monitor)

PowerPC Options

The following options are specific to the PowerPC emulation:

• -prep

Simulate a PREP system (default is PowerMAC)

• -g WxH[xDEPTH]

Set the initial VGA graphic mode. The default is 800x600x15.

Keys

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

• Ctrl-Alt-f

  Toggle full screen

• Ctrl-Alt-n

  Switch to virtual console 'n'. Standard console mappings are:

  • 1 : Target system display
  • 2 : Monitor
  • 3 :Serial port
• Ctrl-Alt

  Toggle mouse and keyboard grab.

• In the virtual consoles, you can use Ctrl-Up, Ctrl-Down, Ctrl-PageUp and Ctrl-PageDown to move in the back log.
• During emulation, if you are using the -nographic option, use Ctrl-a h to get terminal commands:
  • Ctrl-a h

    Print this help

  • Ctrl-a x

    Exit emulatior

  • Ctrl-a s

    Save disk data back to file (if -snapshot)

  • Ctrl-a b

    Send break (magic sysrq in Linux)

  • Ctrl-a c

    Switch between console and monitor

  • Ctrl-a Ctrl-a

    Send Ctrl-a

SEE ALSO

The HTML documentation of QEMU for more precise information and Linux user mode emulator invocation.

AUTHOR

Fabrice Bellard

Edit Log

• 2005-06-25: Added contents of manpage