RDEV(8) 						     Linux Programmer's Manual							   RDEV(8)

NAME

       rdev - query/set image root device, RAM disk size, or video mode

SYNOPSIS

       rdev [ -rvh ] [ -o offset ] [ image [ value [ offset ] ] ]
       rdev [ -o offset ] [ image [ root_device [ offset ] ] ]
       ramsize [ -o offset ] [ image [ size [ offset ] ] ]
       vidmode [ -o offset ] [ image [ mode [ offset ] ] ]
       rootflags [ -o offset ] [ image [ flags [ offset ] ] ]

DESCRIPTION

       With  no  arguments,  rdev  outputs an /etc/mtab line for the current root file system.	With no arguments, ramsize, vidmode, and rootflags
       print usage information.

       In a bootable image for the Linux kernel on i386, there are several pairs of bytes which specify the root device, the video mode,  and  the
       size of the RAM disk.  These pairs of bytes, by default, begin at offset 504 (decimal) in the kernel image:

	       498 Root flags
	      (500 and 502 Reserved)
	       504 RAM Disk Size
	       506 VGA Mode
	       508 Root Device
	      (510 Boot Signature)

       rdev will change these values.

       Typical values for the image parameter, which is a bootable Linux kernel image, might be:

	      /vmlinux
	      /vmunix
	      /boot/bzImage-2.4.0
	      /dev/fd0
	      /dev/fd1

       When using the rdev command, the root_device parameter might be something like:

	      /dev/hda1
	      /dev/hdf13
	      /dev/sda2
	      /dev/sdc4
	      /dev/ida/c0d0p1

       One may also specify the device by a comma-separated pair of decimal integers major,minor.

       For the ramsize command, the size parameter specifies the size of the RAM disk in kilobytes.

       For  the  rootflags  command,  the  flags parameter contains extra information used when mounting root.	Currently the only effect of these
       flags is to force the kernel to mount the root filesystem in readonly mode if flags is non-zero.

       For the vidmode command, the mode parameter specifies the video mode:

	      -3 = Prompt
	      -2 = Extended VGA
	      -1 = Normal VGA
	       0 = as if "0" was pressed at the prompt
	       1 = as if "1" was pressed at the prompt
	       2 = as if "2" was pressed at the prompt
	       n = as if "n" was pressed at the prompt

       If the value is not specified, the image will be examined to determine the current settings.

OPTIONS

       -r     Causes rdev to act like ramsize.

       -R     Causes rdev to act like rootflags.

       -v     Causes rdev to act like vidmode.

       -h     Provides help.

BUGS

       The rdev utility, when used other than to find a name for the current root device, is an ancient hack that works by patching a kernel image
       at  a  magic  offset  with  magic  numbers. It does not work on architectures other than i386.  Its use is strongly discouraged. Use a boot
       loader like SysLinux or LILO instead.

HISTORY

       At offset 502 there used to be the device number of the swap device (in Linux 0.12), and "rdev -s" or "swapdev" would set  this.   However,
       since Linux 0.95 this constant is not used any longer, and the swap device is specified using the swapon() system call.

AUTHORS

       Originally by Werner Almesberger (almesber@nessie.cs.id.ethz.ch)
       Modified by Peter MacDonald (pmacdona@sanjuan.UVic.CA)
       rootflags support added by Stephen Tweedie (sct@dcs.ed.ac.uk)

Linux 0.99							 20 November 1993							   RDEV(8)