Boot options

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Other name freeldr.ini options

The kernel command line is a text string that is passed to ReactOS by the boot loader (usually FreeLoader). It consists of several switches, each of which has a special meaning to ReactOS. A switch is a forward slash (/) followed by a text string (the name of the switch), and optionally an equal sign (=) and a text string (the value). If the equal sign is present, then at least one value is required to follow.

The syntax, variables, and device strings used by FreeLoader conform to the ARC firmware and boot specification, similarly to the boot system used in all Windows NT implementations (such as the Windows NT boot loader on the x86 architecture, or the ARC console used to boot Windows NT 4.0 on the MIPS, Alpha AXP, and PowerPC architectures). Because of this, boot disks and other firmware- or BIOS-accessible devices are specified by each of the bus, disk, slice, and partition values associated with the device.

In FreeLoader the kernel command line is specified in an Options setting in freeldr.ini. The following text is an example of the contents of freeldr.ini, which boots ReactOS from the first partition of the first IDE drive of the computer system:


As used in the above sample file, DEBUGPORT is a boot option. By adding the boot option /DEBUGREPORT=SCREEN, ReactOS will print debugging information to the screen.


The following boot options may be used:

Turn on debugging output. This option is automatically turned on when building debug version.

To specify output device use DEBUGPORT option. If DEBUGPORT is not specified output by default goes to COM1.

  • Format: DEBUG
Specifying DEBUGPORT as a boot option will enable certain debugging features.
    Any one of the following values may set:
    • SCREEN: Send debug output to the screen.
    • BOCHS: Send debug output to bochs.
    • GDB: Enable the GNU debugger (GDB) stub so remote debugging using GDB is possible.
    • PICE: Enable the Private ICE driver so debugging using Private ICE is possible.
    • COM1: Send debug output to COM1.
    • COM2: Send debug output to COM2.
    • COM3: Send debug output to COM3.
    • COM4: Send debug output to COM4.
    • COM:[hex address]: Specifies the COM I/O port address. (Example: /DEBUGPORT=COM:0xCC00 --here 0xCC00 is base I/O port number)
    • FILE: Send debug output to a file %systemroot%/reactos/debug.log
    • MDA: Send debug output to MDA (The old text graphic card from IBM).

It is allowed to use several DEBUGPORT options, but for ports of the same class, for example, COM ports, only the one (last one) will be used for output.

Specifies baudrate of the serial port to be [baudrate] bps. Used in conjunction with COM1-4 or GDB.
  • Format: BAUDRATE=[baudrate]
Specifies the IRQ number of the serial port to be [irq-number]. Used in conjunction with COM1-4 or GDB.
  • Format: IRQ=[irq-number]
Enables profiling. Profiling information will be written in %windir%\profiler.log. This will slow down the system quite a bit.
  • Format: PROFILE
Will restrict ReactOS to use only the first [maxmem] MB of physical memory.
  • Format: MAXMEM=[maxmem]
disables the bitmap that displays the progress bar at ReactOS startup.
Set up exceptions to be passed to debugger on its occurrence, before being handled by regular exception handling code.
loads the Registry SYSTEM hive as a volatile hive, such, that changes made to it in memory are not saved back to the hive image, into registry file. Useful for running ReactOS from liveCD.
The /SOS parameter displays the names of the drivers as they load during the boot process.

See also: List of Windows NTLDR options (Wikipedia link)