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RDEV
!!!RDEV
NAME
SYNOPSIS
DESCRIPTION
OPTIONS
BUGS
HISTORY
AUTHORS
----
!!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
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
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)
----

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Last edited on Monday, June 3, 2002 6:56:48 pm by "perry"

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