bochsrc man page

bochsrc — Configuration file for Bochs.


Bochsrc is the configuration file that specifies where Bochs should look for disk images, how the Bochs emulation layer should work, etc. The syntax used for bochsrc can also be used as command line arguments for Bochs. The .bochsrc file should be placed either in the current directory before running Bochs or in your home directory.

Starting with Bochs 1.3, you can use environment variables in the bochsrc file, for example:

floppya: 1_44="$IMAGES/bootdisk.img", status=inserted

Starting with version 2.0, two environment variables have a built-in default value which is set at compile time. $BXSHARE points to the "share" directory which is typically /usr/share/bochs on UNIX machines. See the $(sharedir) variable in the Makefile for the exact value. $BXSHARE is used by disk images to locate the directory where the BIOS images and keymaps can be found. If $BXSHARE is not defined, Bochs will supply the default value. Also, $LTDL_LIBRARY_PATH points to a list of directories (separated by colons if more than one) to search in for Bochs plugins. A compile-time default is provided if this variable is not defined by the user.



This option includes another configuration file. It is possible to put installation defaults in a global config file (e.g. location of rom images).

#include /etc/bochsrc


Controls the presence of optional device plugins. These plugins are loaded directly with this option and some of them install a config option that is only available when the plugin device is loaded. The value "1" means to load the plugin and "0" will unload it (if loaded before).

These plugins will be loaded by default (if present): 'biosdev', 'extfpuirq', 'gameport', 'iodebug','parallel', 'serial', 'speaker' and 'unmapped'.

These plugins are also supported, but they are usually loaded directly with their bochsrc option: 'e1000', 'es1370', 'ne2k', 'pcidev', 'pcipnic', 'sb16', 'usb_ohci', 'usb_uhci' and 'usb_xhci'.

This plugin currently must be loaded with plugin_ctrl: 'voodoo'.

plugin_ctrl: unmapped=0, e1000=1 # unload 'unmapped' and load 'e1000'


The configuration interface is a series of menus or dialog boxes that allows you to change all the settings that control Bochs's behavior. Depending on the platform there are up to 3 choices of configuration interface: a text mode version called "textconfig" and two graphical versions called "win32config" and "wx". The text mode version uses stdin/stdout and is always compiled in, unless Bochs is compiled for wx only. The choice "win32config" is only available on win32 and it is the default there. The choice "wx" is only available when you use "--with-wx" on the configure command. If you do not write a config_interface line, Bochs will choose a default for you.

NOTE: if you use the "wx" configuration interface, you must also use the "wx" display library.

config_interface: textconfig


The display library is the code that displays the Bochs VGA screen. Bochs has a selection of about 10 different display library implementations for different platforms. If you run configure with multiple --with-* options, the display_library command lets you choose which one you want to run with. If you do not write a display_library line, Bochs will choose a default for you.

The choices are:
x X windows interface, cross platform
win32 native win32 libraries
carbon Carbon library (for MacOS X)
macintosh MacOS pre-10
amigaos native AmigaOS libraries
sdl SDL library, cross platform
term text only, uses curses/ncurses library, cross platform
rfb provides an interface to AT&T's VNC viewer, cross platform
wx wxWidgets library, cross platform
nogui no display at all

NOTE: if you use the "wx" configuration interface, you must also use the "wx" display library.

Specific options: Some display libraries now support specific options to control their behaviour. These options are supported by more than one display library:

"gui_debug" - use GTK debugger gui (sdl, x)
"hideIPS" - disable IPS output in status bar (rfb, sdl, wx, x)
"nokeyrepeat" - turn off host keyboard repeat (sdl, x)

See the examples below for other currently supported options.

display_library: x
display_library: rfb, options="timeout=60" # time to wait for client
display_library: sdl, options="fullscreen" # startup in fullscreen mode


The ROM BIOS controls what the PC does when it first powers on. Normally, you can use a precompiled BIOS in the source or binary distribution called BIOS-bochs-latest. The default ROM BIOS is usually loaded starting at address 0xe0000, and it is exactly 128k long. The legacy version of the Bochs BIOS is usually loaded starting at address 0xf0000, and it is exactly 64k long. You can also use the environment variable $BXSHARE to specify the location of the BIOS. The usage of external large BIOS images (up to 512k) at memory top is now supported, but we still recommend to use the BIOS distributed with Bochs. The start address is optional, since it can be calculated from image size.

romimage: file=bios/BIOS-bochs-latest
romimage: file=$BXSHARE/BIOS-bochs-legacy
romimage: file=mybios.bin, address=0xfff80000
romimage: file=mybios.bin


This defines cpu-related parameters inside Bochs:


Set the number of processors:cores per processor:threads per core when Bochs is compiled for SMP emulation. Bochs currently supports up to 8 processors. If Bochs is compiled without SMP support, it won't accept values different from 1.


Maximum amount of instructions allowed to execute by processor before returning control to another cpu. This option exists only in Bochs binary compiled with SMP support.


Reset the CPU when triple fault occur (highly recommended) rather than PANIC. Remember that if you trying to continue after triple fault the simulation will be completely bogus !


Determine whether to limit maximum CPUID function to 2. This mode is required to workaround WinNT installation and boot issues.


When this option is enabled MWAIT will not put the CPU into a sleep state. This option exists only if Bochs compiled with --enable-monitor-mwait.


Define path to user CPU Model Specific Registers (MSRs) specification. See example in msrs.def.


Ignore MSR references that Bochs does not understand; print a warning message instead of generating #GP exception. This option is enabled by default but will not be avaiable if configurable MSRs are enabled.


Emulated Instructions Per Second. This is the number of IPS that Bochs is capable of running on your machine. You can recompile Bochs with --enable-show-ips option enabled, to find your workstation's capability. Measured IPS value will then be logged into your log file or status bar (if supported by the gui).

IPS is used to calibrate many time-dependent events within the bochs simulation. For example, changing IPS affects the frequency of VGA updates, the duration of time before a key starts to autorepeat, and the measurement of BogoMips and other benchmarks.

Example Specifications[1]
Bochs Machine/Compiler Mips
2.4.6 3.4Ghz Intel Core i7 2600 with Win7x64/g++ 4.5.2 85 to 95 Mips
2.3.7 3.2Ghz Intel Core 2 Q9770 with WinXP/g++ 3.4 50 to 55 Mips
2.3.7 2.6Ghz Intel Core 2 Duo with WinXP/g++ 3.4 38 to 43 Mips
2.2.6 2.6Ghz Intel Core 2 Duo with WinXP/g++ 3.4 21 to 25 Mips
2.2.6 2.1Ghz Athlon XP with Linux 2.6/g++ 3.4 12 to 15 Mips

[1] IPS measurements depend on OS and compiler configuration in addition to processor clock speed.

cpu: count=2, ips=10000000, msrs="msrs.def"


This defines features and functionality supported by Bochs emulated CPU:


Set emulated CPU level information returned by CPUID. Default value is determined by configure option --enable-cpu-level. Currently supported values are 5 (for Pentium and similar processors) and 6 (for P6 and later processors).


Set family information returned by CPUID. Default family value determined by configure option --enable-cpu-level.


Set model information returned by CPUID. Default model value is 3.


Set stepping information returned by CPUID. Default stepping value is 3.


Set the CPUID vendor string returned by CPUID(0x0). This should be a twelve-character ASCII string.


Set the CPUID vendor string returned by CPUID(0x80000002 .. 0x80000004). This should be at most a forty-eight-character ASCII string.


Select MMX instruction set support. This option exists only if Bochs compiled with BX_CPU_LEVEL >= 5.


Select APIC configuration (LEGACY/XAPIC/XAPIC_EXT/X2APIC). This option exists only if Bochs compiled with BX_CPU_LEVEL >= 5.


Select SYSENTER/SYSEXIT instruction set support. This option exists only if Bochs compiled with BX_CPU_LEVEL >= 6.


Select SSE instruction set support. Any of NONE/SSE/SSE2/SSE3/SSSE3/SSE4_1/SSE4_2 could be selected. This option exists only if Bochs compiled with BX_CPU_LEVEL >= 6.


Select AMD SSE4A instructions support. This option exists only if Bochs compiled with BX_CPU_LEVEL >= 6.


Select AMD Misaligned SSE mode support. This option exists only if Bochs compiled with BX_CPU_LEVEL >= 6.


Select AES instruction set support. This option exists only if Bochs compiled with BX_CPU_LEVEL >= 6.


Select MOVBE Intel(R) Atom instruction support. This option exists only if Bochs compiled with BX_CPU_LEVEL >= 6.


Select ADCX/ADOX instructions support. This option exists only if Bochs compiled with BX_CPU_LEVEL >= 6.


Select XSAVE extensions support. This option exists only if Bochs compiled with BX_CPU_LEVEL >= 6.


Select XSAVEOPT instruction support. This option exists only if Bochs compiled with BX_CPU_LEVEL >= 6.


Select AVX/AVX2 instruction set support. This option exists only if Bochs compiled with --enable-avx option.


Select AVX float16 convert instructions support. This option exists only if Bochs compiled with --enable-avx option.


Select AVX fused multiply add (FMA) instructions support. This option exists only if Bochs compiled with --enable-avx option.


Select BMI1/BMI2 instructions support. This option exists only if Bochs compiled with --enable-avx option.


Select AMD four operand FMA instructions support. This option exists only if Bochs compiled with --enable-avx option.


Select AMD XOP instructions support. This option exists only if Bochs compiled with --enable-avx option.


Select AMD TBM instructions support. This option exists only if Bochs compiled with --enable-avx option.


Enable x85-64 and long mode support. This option exists only if Bochs compiled with x86-64 support.


Enable 1G page size support in long mode. This option exists only if Bochs compiled with x86-64 support.


Enable Process-Context Identifiers (PCID) support in long mode. This option exists only if Bochs compiled with x86-64 support.


Enable Supervisor Mode Execution Protection (SMEP) support. This option exists only if Bochs compiled with BX_CPU_LEVEL >= 6.


Enable Supervisor Mode Access Prevention (SMAP) support. This option exists only if Bochs compiled with BX_CPU_LEVEL >= 6.


Select MONITOR/MWAIT instructions support. This option exists only if Bochs compiled with --enable-monitor-mwait.


Select VMX extensions emulation support. This option exists only if Bochs compiled with --enable-vmx option.


Select AMD SVM (Secure Virtual Machine) extensions emulation support. This option exists only if Bochs compiled with --enable-svm option.

cpuid: mmx=1, sep=1, sse=sse4_2, xapic=1, aes=1, movbe=1, xsave=1


Set the amount of physical memory you want to emulate.


Set amount of guest physical memory to emulate. The default is 32MB, the maximum amount limited only by physical address space limitations.


Set amount of host memory you want to allocate for guest RAM emulation. It is possible to allocate less memory than you want to emulate in guest system. This will fake guest to see the non-existing memory. Once guest system touches new memory block it will be dynamically taken from the memory pool. You will be warned (by FATAL PANIC) in case guest already used all allocated host memory and wants more.

memory: guest=512, host=256


The 'megs:' option sets the 'guest' and 'host' memory parameters to the same value. In all other cases the 'memory' option should be used instead.

megs: 32

optromimage1: , optromimage2: , optromimage3: or optromimage4:

You may now load up to 4 optional ROM images. Be sure to use a read-only area, typically between C8000 and EFFFF. These optional ROM images should not overwrite the rombios (located at F0000-FFFFF) and the videobios (located at C0000-C7FFF). Those ROM images will be initialized by the bios if they contain the right signature (0x55AA). It can also be a convenient way to upload some arbitrary code/data in the simulation, that can be retrieved by the boot loader

optromimage1: file=optionalrom.bin, address=0xd0000


You also need to load a VGA ROM BIOS into 0xC0000.

vgaromimage: file=bios/VGABIOS-elpin-2.40
vgaromimage: file=bios/VGABIOS-lgpl-latest
vgaromimage: file=$BXSHARE/VGABIOS-lgpl-latest


This defines parameters related to the VGA display.


Here you can specify the display extension to be used. With the value 'none' you can use standard VGA with no extension. Other supported values are 'vbe' for Bochs VBE and 'cirrus' for Cirrus SVGA support.


The VGA update frequency is based on the emulated clock and the default value is 5. Keep in mind that you must tweak the 'cpu: ips=N' directive to be as close to the number of emulated instructions-per-second your workstation can do, for this to be accurate. If the realtime sync is enabled with the 'clock' option, the value is based on the real time. This parameter can be changed at runtime.

vga: extension=cirrus, update_freq=10
vga: extension=vbe

floppya: or floppyb:

Point this to the pathname of a floppy image file or device. Floppya is the first drive, and floppyb is the second drive. If you're booting from a floppy, floppya should point to a bootable disk.

You can set the initial status of the media to 'ejected' or 'inserted'. Usually you will want to use 'inserted'.

The parameter 'type' can be used to enable the floppy drive without media and status specified. Usually the drive type is set up based on the media type.

The optional parameter 'write_protected' can be used to control the media write protect switch. By default it is turned off.


2.88M 3.5" media:
floppya: 2_88=path, status=ejected

1.44M 3.5" media (write protected):
floppya: 1_44=path, status=inserted, write_protected=1

1.2M 5.25" media:
floppyb: 1_2=path, status=ejected

720K 3.5" media:
floppya: 720k=path, status=inserted

360K 5.25" media:
floppya: 360k=path, status=inserted

Autodetect floppy media type:
floppya: image=path, status=inserted

Use directory as 1.44M VFAT media:
floppya: 1_44=vvfat:path, status=inserted

1.44M 3.5" floppy drive, no media:
floppya: type=1_44

ata0: , ata1: , ata2: or ata3:

These options enables up to 4 ata channels. For each channel the two base io addresses and the irq must be specified. ata0 and ata1 are enabled by default, with the values shown below.

ata0: enabled=1, ioaddr1=0x1f0, ioaddr2=0x3f0, irq=14
ata1: enabled=1, ioaddr1=0x170, ioaddr2=0x370, irq=15
ata2: enabled=1, ioaddr1=0x1e8, ioaddr2=0x3e0, irq=11
ata3: enabled=1, ioaddr1=0x168, ioaddr2=0x360, irq=9

ata[0-3]-master: or ata[0-3]-slave:

This defines the type and characteristics of all attached ata devices:
type= type of attached device [disk|cdrom]
path= path of the image
mode= image mode [flat|concat|external|dll|sparse|vmware3|vmware4|undoable|growing|volatile|vpc|vvfat], only valid for disks
cylinders= only valid for disks
heads= only valid for disks
spt= only valid for disks
status= only valid for cdroms [inserted|ejected]
biosdetect= type of biosdetection [none|auto], only for disks on ata0 [cmos]
translation=type of translation of the bios, only for disks [none|lba|large|rechs|auto]
model= string returned by identify device command
journal= optional filename of the redolog for undoable, volatile and vvfat disks

Point this at a hard disk image file, cdrom iso file, or a physical cdrom device. To create a hard disk image, try running bximage. It will help you choose the size and then suggest a line that works with it.

In UNIX it is possible to use a raw device as a Bochs hard disk, but WE DON'T RECOMMEND IT.

The path is mandatory for hard disks. Disk geometry autodetection works with images created by bximage if CHS is set to 0/0/0 (cylinders are calculated using heads=16 and spt=63). For other hard disk images and modes the cylinders, heads, and spt are mandatory. In all cases the disk size reported from the image must be exactly C*H*S*512.

The mode option defines how the disk image is handled. Disks can be defined as:
- flat : one file flat layout
- concat : multiple files layout
- external : developer's specific, through a C++ class
- dll : developer's specific, through a DLL
- sparse : stackable, commitable, rollbackable
- vmware3 : vmware3 disk support
- vmware4 : vmware4 disk support (aka VMDK)
- undoable : flat file with commitable redolog
- growing : growing file
- volatile : flat file with volatile redolog
- vpc : fixed / dynamic size VirtualPC image
- vvfat: local directory appears as read-only VFAT disk (with volatile redolog)

The disk translation scheme (implemented in legacy int13 bios functions, and used by older operating systems like MS-DOS), can be defined as:
- none : no translation, for disks up to 528MB (1032192 sectors)
- large : a standard bitshift algorithm, for disks up to 4.2GB (8257536 sectors)
- rechs : a revised bitshift algorithm, using a 15 heads fake physical geometry, for disks up to 7.9GB (15482880 sectors). (don't use this unless you understand what you're doing)
- lba : a standard lba-assisted algorithm, for disks up to 8.4GB (16450560 sectors)
- auto : autoselection of best translation scheme. (it should be changed if system does not boot)

Default values are:
mode=flat, biosdetect=auto, translation=auto, model="Generic 1234"

The biosdetect option has currently no effect on the bios

ata0-master: type=disk, path=10M.sample, cylinders=306, heads=4, spt=17
ata0-slave: type=disk, path=20M.sample, cylinders=615, heads=4, spt=17
ata1-master: type=disk, path=30M.sample, cylinders=615, heads=6, spt=17
ata1-slave: type=disk, path=46M.sample, cylinders=940, heads=6, spt=17
ata2-master: type=disk, path=62M.sample, cylinders=940, heads=8, spt=17
ata2-slave: type=disk, path=112M.sample, cylinders=900, heads=15, spt=17
ata3-master: type=disk, path=483M.sample, cylinders=1024, heads=15, spt=63
ata3-slave: type=cdrom, path=iso.sample, status=inserted

com1: , com2: , com3: or com4:

This defines a serial port (UART type 16550A). In the 'term' mode you can specify a device to use as com1. This can be a real serial line, or a pty. To use a pty (under X/Unix), create two windows (xterms, usually). One of them will run bochs, and the other will act as com1. Find out the tty the com1 window using the `tty' command, and use that as the `dev' parameter. Then do `sleep 1000000' in the com1 window to keep the shell from messing with things, and run bochs in the other window. Serial I/O to com1 (port 0x3f8) will all go to the other window.

Other serial modes are 'null' (no input/output), 'file' (output to a file specified as the 'dev' parameter), 'raw' (use the real serial port - under construction for win32) and 'mouse' (standard serial mouse - requires mouse option setting 'type=serial' or 'type=serial_wheel')

com1: enabled=1, mode=term, dev=/dev/ttyp7
com2: enabled=1, mode=file, dev=serial.out
com1: enabled=1, mode=mouse

parport1: or parport2:

This defines a parallel (printer) port. When turned on and an output file is defined the emulated printer port sends characters printed by the guest OS into the output file. On some platforms a device filename can be used to send the data to the real parallel port (e.g. "/dev/lp0" on Linux).

parport1: enabled=1, file=parport.out
parport2: enabled=1, file="/dev/lp0"
parport1: enabled=0


This defines the boot sequence. Now you can specify up to 3 boot drives, which can be 'floppy', 'disk', 'cdrom' or 'network' (boot ROM). Legacy 'a' and 'c' are also supported.

boot: cdrom, floppy, disk


This disables the 0xaa55 signature check on boot floppies The check is enabled by default.

floppy_bootsig_check: disabled=1


Give the path of the log file you'd like Bochs debug and misc. verbiage to be written to. If you really don't want it, make it /dev/null.

log: bochs.out
log: /dev/tty (unix only)
log: /dev/null (unix only)


This handles the format of the string prepended to each log line : You may use those special tokens :
%t : 11 decimal digits timer tick
%i : 8 hexadecimal digits of cpu0 current eip
%e : 1 character event type ('i'nfo, 'd'ebug, 'p'anic, 'e'rror)
%d : 5 characters string of the device, between brackets

Default : %t%e%d

logprefix: %t-%e-@%i-%d
logprefix: %i%e%d


If Bochs reaches a condition where it cannot emulate correctly, it does a panic. This can be a configuration problem (like a misspelled bochsrc line) or an emulation problem (like an unsupported video mode). The "panic" setting in bochsrc tells Bochs how to respond to a panic. You can set this to fatal (terminate the session), report (print information to the console), or ignore (do nothing).

The safest setting is action=fatal. If you are getting panics, you can try action=report instead. If you allow Bochs to continue after a panic, don't be surprised if you get strange behavior or crashes if a panic occurs. Please report panic messages unless it is just a configuration problem like "could not find hard drive image."

panic: action=fatal


Bochs produces an error message when it finds a condition that really shouldn't happen, but doesn't endanger the simulation. An example of an error might be if the emulated software produces an illegal disk command.

The "error" setting tells Bochs how to respond to an error condition. You can set this to fatal (terminate the session), report (print information to the console), or ignore (do nothing).

error: action=report


This setting tells Bochs what to do when an event occurs that generates informational messages. You can set this to fatal (that would not be very smart though), report (print information to the console), or ignore (do nothing). For general usage, the "report" option is probably a good choice.

info: action=report


This setting tells Bochs what to do with messages intended to assist in debugging. You can set this to fatal (but you shouldn't), report (print information to the console), or ignore (do nothing). You should generally set this to ignore, unless you are trying to diagnose a particular problem.

NOTE: When action=report, Bochs may spit out thousands of debug messages per second, which can impact performance and fill up your disk.

debug: action=ignore


Give the path of the log file you'd like Bochs to log debugger output. If you really don't want it, make it '/dev/null', or '-'.

log: debugger.out
log: /dev/null (unix only)
log: -


This defines the SB16 sound emulation. It can have several of the following properties. All properties are in this format:
sb16: property=value



The filename is where the midi data is sent. This can be a device or just a file if you want to record the midi data.


0 = No data should be output.
1 = output to device (system dependent - midi
denotes the device driver).
2 = SMF file output, including headers.
3 = Output the midi data stream to the file
(no midi headers and no delta times, just
command and data bytes).


This is the device/file where wave output is stored.


0 = no data
1 = output to device (system dependent - wave
denotes the device driver).
2 = VOC file output, including headers.
3 = Output the raw wave stream to the file.


The file to write the sb16 emulator messages to.


0 = No log.
1 = Resource changes, midi program and bank changes.
2 = Severe errors.
3 = All errors.
4 = All errors plus all port accesses.
5 = All errors and port accesses plus a lot
of extra information.

It is possible to change the loglevel at runtime.


Microseconds per second for a DMA cycle. Make it smaller to fix non-continuous sound. 750000 is usually a good value. This needs a reasonably correct setting for the IPS parameter of the CPU option. It is possible to adjust the dmatimer at runtime.

Example for output to OSS:
sb16: midimode=1, midi=/dev/midi00,
wavemode=1, wave=/dev/dsp, loglevel=2,
log=sb16.log, dmatimer=600000

Example for output to ALSA:
sb16: midimode=1, midi=alsa:128:0,
wavemode=1, wave=alsa,
log=sb16.log, dmatimer=600000

Example for output using SDL:
sb16: wavemode=1, wave=sdl

NOTE: The examples are wrapped onto three lines for formatting reasons, but it should all be on one line in the actual bochsrc file.


This defines the ES1370 sound emulation. The parameter 'enabled' controls the presence of the device. The 'wavedev' parameter is similar to the 'wave' parameter of the SB16 soundcard. The emulation supports recording and playback (except DAC1+DAC2 output at the same time).

es1370: enabled=1, wavedev="" # win32
es1370: enabled=1, wavedev=alsa # Linux with ALSA
es1370: enabled=1, wavedev=sdl # use SDL audio (if present) for output


This defines parameters related to the emulated keyboard:


Type of keyboard return by a "identify keyboard" command to the keyboard controller. It must be one of "xt", "at" or "mf". Defaults to "mf". It should be ok for almost everybody. A known exception is french macs, that do have a "at"-like keyboard.


Approximate time in microseconds that it takes one character to be transferred from the keyboard to controller over the serial path.


Approximate time in microseconds between attempts to paste characters to the keyboard controller. This leaves time for the guest os to deal with the flow of characters. The ideal setting depends on how your operating system processes characters. The default of 100000 usec (.1 seconds) was chosen because it works consistently in Windows.

If your OS is losing characters during a paste, increase the paste delay until it stops losing characters.


This enables a remap of a physical localized keyboard to a virtualized us keyboard, as the PC architecture expects.


This defines the keyboard shortcut to be sent when you press the "user" button in the header bar. The shortcut string is a combination of maximum 3 key names (listed below) separated with a '-' character.

Valid key names:

"alt", "bksl", "bksp", "ctrl", "del", "down", "end", "enter", "esc", "f1", ... "f12", "home", "ins", "left", "menu", "minus", "pgdwn", "pgup", "plus", "right", "shift", "space", "tab", "up", "win", "print" and "power".

keyboard: type=mf, serial_delay=200, paste_delay=100000
keyboard: keymap=gui/keymaps/x11-pc-de.map
keyboard: user_shortcut=ctrl-alt-del


This defines the parameters of the clock inside Bochs.


This defines the method how to synchronize the Bochs internal time with realtime. With the value 'none' the Bochs time relies on the IPS value and no host time synchronization is used. The 'slowdown' method sacrifices performance to preserve reproducibility while allowing host time correlation. The 'realtime' method sacrifices reproducibility to preserve performance and host-time correlation. It is possible to enable both synchronization methods.


Specifies the start (boot) time of the virtual machine. Use a time value as returned by the time(2) system call. If no time0 value is set or if time0 equal to 1 (special case) or if time0 equal 'local', the simulation will be started at the current local host time. If time0 equal to 2 (special case) or if time0 equal 'utc', the simulation will be started at the current utc time.

clock: sync=[none|slowdown|realtime|both], time0=[timeValue|local|utc]

Default value are sync=none, time0=local

clock: sync=realtime, time0=938581955 # Wed Sep 29 07:12:35 1999


This defines parameters for the emulated mouse type, the initial status of the mouse capture and the runtime method to toggle it.


With the mouse type option you can select the type of mouse to emulate. The default value is 'ps2'. The other choices are 'imps2' (wheel mouse on PS/2), 'serial', 'serial_wheel' and 'serial_msys' (one com port requires setting 'mode=mouse'). To connect a mouse to an USB port, see the 'usb_uhci', 'usb_ohci' or 'usb_xhci' option (requires PCI and USB support).


The Bochs gui creates mouse "events" unless the 'enabled' option is set to 0. The hardware emulation itself is not disabled by this. Unless you have a particular reason for enabling the mouse by default, it is recommended that you leave it off. You can also toggle the mouse usage at runtime (RFB, SDL, Win32, wxWidgets and X11 - see below).


The default method to toggle the mouse capture at runtime is to press the CTRL key and the middle mouse button ('ctrl+mbutton'). This option allows to change the method to 'ctrl+f10' (like DOSBox), 'ctrl+alt' (like QEMU) or 'f12' (replaces win32 'legacyF12' option).

mouse: enabled=1
mouse: type=imps2, enabled=1
mouse: type=serial, enabled=1
mouse: enabled=0, toggle=ctrl+f10


Requests that the GUI create and use it's own non-shared colormap. This colormap will be used when in the bochs window. If not enabled, a shared colormap scheme may be used. Once again, enabled=1 turns on this feature and 0 turns it off.

private_colormap: enabled=1


This option controls the presence of a PCI chipset in Bochs. Currently it only supports the i440FX chipset. You can also specify the devices connected to PCI slots. Up to 5 slots are available. For these combined PCI/ISA devices assigning to slot is mandatory if you want to emulate the PCI model: cirrus, ne2k and pcivga. These PCI-only devices are also supported, but they are auto-assigned if you don't use the slot configuration: e1000, es1370, pcidev, pcipnic, usb_ohci and usb_xhci.

pci: enabled=1, chipset=i440fx, slot1=pcivga, slot2=ne2k


Enables the mapping of a host PCI hardware device within the PCI subsystem of the Bochs x86 emulator. This feature requires Linux as a host OS.

pcidev: vendor=0x1234, device=0x5678

The vendor and device arguments should contain the vendor ID respectively the device ID of the PCI device you want to map within Bochs. The PCI mapping is still very experimental.


Defines the characteristics of an attached ne2000 isa card :


IOADDR, IRQ: You probably won't need to change ioaddr and irq, unless there are IRQ conflicts. These parameters are ignored if the NE2000 is assigned to a PCI slot.

MAC: The MAC address MUST NOT match the address of any machine on the net. Also, the first byte must be an even number (bit 0 set means a multicast address), and you cannot use ff:ff:ff:ff:ff:ff because that's the broadcast address. For the ethertap module, you must use fe:fd:00:00:00:01. There may be other restrictions too. To be safe, just use the b0:c4... address.

ETHMOD: The ethmod value defines which low level OS specific module to be used to access physical ethernet interface. Current implemented values include
- fbsd : ethernet on freebsd and openbsd
- linux : ethernet on linux
- win32 : ethernet on win32
- tap : ethernet through a linux tap interface
- tuntap : ethernet through a linux tuntap interface
- slirp : ethernet backend for Slirp with builtin DHCP / TFTP servers

If you don't want to make connections to any physical networks, you can use the following 'ethmod's to simulate a virtual network.
- null : All packets are discarded, but logged to a few files
- vde : Virtual Distributed Ethernet
- vnet : ARP, ICMP-echo(ping), DHCP and TFTP are simulated
The virtual host uses
DHCP assigns to the guest
The TFTP server use 'ethdev' for the root directory and doesn't
overwrite files

ETHDEV: The ethdev value is the name of the network interface on your host platform. On UNIX machines, you can get the name by running ifconfig. On Windows machines, you must run niclist to get the name of the ethdev. Niclist source code is in misc/niclist.c and it is included in Windows binary releases.

SCRIPT: The script value is optional, and is the name of a script that is executed after bochs initialize the network interface. You can use this script to configure this network interface, or enable masquerading. This is mainly useful for the tun/tap devices that only exist during Bochs execution. The network interface name is supplied to the script as first parameter.

BOOTROM: The bootrom value is optional, and is the name of the ROM image to load. Note that this feature is only implemented for the PCI version of the NE2000.

ne2k: ioaddr=0x300, irq=9, mac=b0:c4:20:00:00:00, ethmod=fbsd, ethdev=xlo
ne2k: ioaddr=0x300, irq=9, mac=b0:c4:20:00:00:00, ethmod=linux, ethdev=eth0
ne2k: ioaddr=0x300, irq=9, mac=b0:c4:20:00:00:01, ethmod=win32, ethdev=MYCARD
ne2k: ioaddr=0x300, irq=9, mac=fe:fd:00:00:00:01, ethmod=tap, ethdev=tap0
ne2k: ioaddr=0x300, irq=9, mac=fe:fd:00:00:00:01, ethmod=tuntap, ethdev=/dev/net/tun0, script=./tunconfig
ne2k: ioaddr=0x300, irq=9, mac=b0:c4:20:00:00:01, ethmod=vde, ethdev="/tmp/vde.ctl"
ne2k: ioaddr=0x300, irq=9, mac=b0:c4:20:00:00:01, ethmod=vnet, ethdev="c:/temp"
ne2k: mac=b0:c4:20:00:00:01, ethmod=slirp, script=/usr/local/bin/slirp, bootrom=ne2k_pci.rom


To support the Bochs/Etherboot pseudo-NIC, Bochs must be compiled with the --enable-pnic configure option. It accepts the same syntax (for mac, ethmod, ethdev, script, bootrom) and supports the same networking modules as the NE2000 adapter.

pnic: enabled=1, mac=b0:c4:20:00:00:00, ethmod=vnet


To support the Intel(R) 82540EM Gigabit Ethernet adapter, Bochs must be compiled with the --eanble-e1000 configure option. The E1000 accepts the same syntax (for mac, ethmod, ethdev, script, bootrom) and supports the same networking modules as the NE2000 adapter.

e1000: enabled=1, mac=52:54:00:12:34:56, ethmod=slirp, script=/usr/local/bin/slirp


This defines image file that can be loaded into the CMOS RAM at startup. The rtc_init parameter controls whether initialize the RTC with values stored in the image. By default the time0 argument given to the clock option is used. With 'rtc_init=image' the image is the source for the initial time.

cmosimage: file=cmos.img, rtc_init=time0


This option controls the presence of the USB root hub which is a part of the i440FX PCI chipset. With the portX option you can connect devices to the hub (currently supported: 'mouse', 'tablet', 'keypad', 'disk', 'cdrom', 'hub' and 'printer').

The optionsX parameter can be used to assign specific options to the device connected to the corresponding USB port. Currently this feature is only used to set the speed reported by device and by the 'disk' device to specify an alternative redolog file of some image modes.

If you connect the mouse or tablet to one of the ports, Bochs forwards the mouse movement data to the USB device instead of the selected mouse type. When connecting the keypad to one of the ports, Bochs forwards the input of the numeric keypad to the USB device instead of the PS/2 keyboard.

To connect a 'flat' mode image as an USB hardisk you can use the 'disk' device with the path to the image separated with a colon. To use other disk image modes similar to ATA disks the syntax 'disk:mode:filename' must be used (see below).

To emulate an USB cdrom you can use the 'cdrom' device name and the path to an ISO image or raw device name also separated with a colon. An option to insert/eject media is available in the runtime configuration.

The device 'printer' emulates the HP Deskjet 920C printer. The PCL data is sent to a file specified in bochsrc.txt. The current code appends the PCL code to the file if the file already existed. It would probably be nice to overwrite the file instead, asking user first.

usb_uhci: enabled=1, port1=mouse, port2=disk:usbstick.img
usb_uhci: enabled=1, port1=hub:7, port2=disk:growing:usbdisk.img
usb_uhci: enabled=1, port1=printer:printdata.bin, port2=cdrom:image.iso


This option controls the presence of the USB OHCI host controller with a 2-port hub. The portX option accepts the same device types with the same syntax as the UHCI controller (see above).

usb_ohci: enabled=1


This option controls the presence of the experimental USB xHCI host controller with a 4-port hub. The portX option accepts the same device types with the same syntax as the UHCI controller (see above).

usb_xhci: enabled=1


Load user-defined plugin. This option is available only if Bochs is compiled with plugin support. Maximum 8 different plugins are supported. See the example in the Bochs sources how to write a plugin device.

user_plugin: name=testdev


This program is distributed under the terms of the GNU Lesser General Public License as published by the Free Software Foundation. See the License and COPYING files located in /usr/share/doc/bochs/ for details on the license and the lack of warranty.


The latest version of this program can be found at:

See Also

bochs(1), bochs-dlx(1), bximage(1), bxcommit(1)

The Bochs IA-32 Emulator site on the World Wide Web:

Online Bochs Documentation


The Bochs emulator was created by Kevin Lawton (kevin@mandrakesoft.com), and is currently maintained by the members of the Bochs x86 Emulator Project. You can see a current roster of members at:


Please report all bugs to the bug tracker on our web site. Just go to http://bochs.sourceforge.net, and click "Bug Reports" on the sidebar under "Feedback".

Provide a detailed description of the bug, the version of the program you are running, the operating system you are running the program on and the operating system you are running in the emulator.

Referenced By

bochs(1), bxcommit(1), bximage(1).

Explore man page connections for bochsrc(5).

bochsrc The Bochs Project 24 Feb 2013