sys-utils/rdev.8

   1 .\" Copyright 1992, 1993 Rickard E. Faith (faith@cs.unc.edu)
   2 .\" May be distributed under the GNU General Public License
   3 .\" Changes from sct@dcs.ed.ac.uk added Sat Oct  9 09:54:00 1993.
   4 .TH RDEV 8 "20 November 1993" "Linux 0.99" "Linux Programmer's Manual"
   5 .SH NAME
   6 rdev \- query/set image root device, swap device, RAM disk size, or video mode
   7 .SH SYNOPSIS
   8 .nf
   9 .BR "rdev [ \-rsvh ] [ \-o " offset " ] [ " image " [ " value " [ " offset " ] ] ]"
  10 .BR "rdev [ \-o " offset " ] [ " image " [ " root_device " [ " offset " ] ] ]"
  11 .BR "swapdev [ \-o " offset " ] [ " image " [ " swap_device " [ " offset " ] ] ]"
  12 .BR "ramsize [ \-o " offset " ] [ " image " [ " size " [ " offset " ] ] ]"
  13 .BR "vidmode [ \-o " offset " ] [ " image " [ " mode " [ " offset " ] ] ]"
  14 .BR "rootflags [ \-o " offset " ] [ " image " [ " flags " [ " offset " ] ] ]"
  15 .fi
  16 .SH DESCRIPTION
  17 .\" " for emacs hilit19
  18 With no arguments,
  19 .B rdev
  20 outputs an
  21 .I /etc/mtab
  22 line for the current root file system.
  23 With no arguments,
  24 .BR swapdev ", " ramsize ", " vidmode ", and " rootflags
  25 print usage information.
  26
  27 In a bootable image for the Linux kernel, there are several pairs of bytes
  28 which specify the root device, the video mode, the size of the RAM disk,
  29 and the swap device.  These pairs of bytes, by default, begin at offset 504
  30 (decimal) in the kernel image:
  31
  32 .nf
  33 .RS
  34  498 Root flags
  35 (500 and 502 Reserved)
  36  504 RAM Disk Size
  37  506 VGA Mode
  38  508 Root Device
  39 (510 Boot Signature)
  40 .RE
  41 .fi
  42
  43 .B rdev
  44 will change these values.
  45
  46 Typical values for the
  47 .I image
  48 parameter, which is a bootable Linux kernel image, might be:
  49
  50 .nf
  51 .RS
  52 /vmlinux
  53 /vmunix
  54 /boot/bzImage-2.4.0
  55 /dev/fd0
  56 /dev/fd1
  57 .RE
  58 .fi
  59
  60 When using the
  61 .BR rdev ", or " swapdev
  62 commands, the
  63 .IR root_device " or " swap_device
  64 parameter might be something like:
  65
  66 .nf
  67 .RS
  68 /dev/hda1
  69 /dev/hdf13
  70 /dev/sda2
  71 /dev/sdc4
  72 /dev/ida/c0d0p1
  73 .RE
  74 .fi
  75
  76 For the
  77 .B ramsize
  78 command, the
  79 .B size
  80 parameter specifies the size of the RAM disk in kilobytes.
  81
  82 For the
  83 .B rootflags
  84 command, the
  85 .B flags
  86 parameter contains extra information used when mounting root.
  87 Currently the only effect of these flags is to force the kernel to
  88 mount the root filesystem in readonly mode if
  89 .B flags
  90 is non-zero.
  91
  92 For the
  93 .B vidmode
  94 command, the
  95 .B mode
  96 parameter specifies the video mode:
  97
  98 .nf
  99 .RS
 100 -3 = Prompt
 101 -2 = Extended VGA
 102 -1 = Normal VGA
 103  0 = as if "0" was pressed at the prompt
 104  1 = as if "1" was pressed at the prompt
 105  2 = as if "2" was pressed at the prompt
 106  n = as if "n" was pressed at the prompt
 107 .RE
 108 .fi
 109
 110 If the
 111 .I value
 112 is not specified, the
 113 .I image
 114 will be examined to determine the current settings.
 115 .SH OPTIONS
 116 .TP
 117 .B \-s
 118 Causes
 119 .B rdev
 120 to act like
 121 .BR swapdev .
 122 .TP
 123 .B \-r
 124 Causes
 125 .B rdev
 126 to act like
 127 .BR ramsize .
 128 .TP
 129 .B \-R
 130 Causes
 131 .B rdev
 132 to act like
 133 .BR rootflags .
 134 .TP
 135 .B \-v
 136 Causes
 137 .B rdev
 138 to act like
 139 .BR vidmode .
 140 .TP
 141 .B \-h
 142 Provides help.
 143 .SH BUGS
 144 For historical reasons, there are two methods for specifying alternative
 145 values for the offset.
 146 .sp
 147 The user interface is cumbersome, non-intuitive, and should probably be
 148 re-written from scratch, allowing multiple kernel image parameters to be
 149 changed or examined with a single command.
 150 .sp
 151 If LILO is used,
 152 .B rdev
 153 is no longer needed for setting the root device and the VGA mode, since
 154 these parameters that
 155 .B rdev
 156 modifies can be set from the LILO prompt during a boot.  However,
 157 .B rdev
 158 is still needed at this time for setting the RAM disk size.  Users are
 159 encouraged to find the LILO documentation for more information, and to use
 160 LILO when booting their systems.
 161 .SH AUTHORS
 162 .nf
 163 Originally by Werner Almesberger (almesber@nessie.cs.id.ethz.ch)
 164 Modified by Peter MacDonald (pmacdona@sanjuan.UVic.CA)
 165 rootflags support added by Stephen Tweedie (sct@dcs.ed.ac.uk)
 166 .fi