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       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 ] ] ]


       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:


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


       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.

               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.


       -r     Causes rdev to act like ramsize.

       -R     Causes rdev to act like rootflags.

       -v     Causes rdev to act like vidmode.

       -h     Provides help.


       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  num­
       bers.  It  does not work on architectures other than i386.
       Its use is strongly discouraged. Use a  boot  loader  like
       SysLinux or LILO instead.


       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.


       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)
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