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

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

SYNOPSIS
       rdev [ -rsvh ] [ -o offset ] [ image [ value [ offset ] ] ]
       rdev [ -o offset ] [ image [ root_device [ offset ] ] ]
       swapdev [ -o offset ] [ image [ swap_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, swapdev,
       ramsize, vidmode, and rootflags print usage information.

       In a bootable image for the Linux kernel, there  are  sev-
       eral  pairs  of  bytes  which specify the root device, the
       video mode, the size of the RAM disk, and the swap device.
       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, are as follows:

              /vmlinux
              /vmlinux.test
              /vmunix
              /vmunix.test
              /dev/fd0
              /dev/fd1

       When  using the rdev, or swapdev commands, the root_device
       or swap_device parameter are as follows:

              /dev/hda[1-8]
              /dev/hdb[1-8]
              /dev/sda[1-8]
              /dev/sdb[1-8]

       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
       -s     Causes rdev to act like swapdev.

       -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
       For historical reasons, there are two methods for specify-
       ing alternative values for the offset.

       The  user  interface  is  cumbersome,  non-intuitive,  and
       should  probably be re-written from scratch, allowing mul-
       tiple kernel image parameters to be  changed  or  examined
       with a single command.

       If  LILO is used, rdev is no longer needed for setting the
       root device and the VGA mode, since these parameters  that
       rdev  modifies  can  be  set from the LILO prompt during a
       boot.  However, rdev is still needed at this time for set-
       ting  the RAM disk size.  Users are encouraged to find the
       LILO documentation for more information, and to  use  LILO
       when booting their systems.

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                       1