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.\" Copyright 1992, 1993 Rickard E. Faith (faith@cs.unc.edu)
.\" May be distributed under the GNU General Public License
.\" Changes from sct@dcs.ed.ac.uk added Sat Oct 9 09:54:00 1993.
.TH RDEV 8 "20 November 1993" "Linux 0.99" "Linux Programmer's Manual"
.SH NAME
rdev \- query/set image root device, swap device, RAM disk size, or video mode
.SH SYNOPSIS
.nf
.BR "rdev [ \-rsvh ] [ \-o " offset " ] [ " image " [ " value " [ " offset " ] ] ]"
.BR "rdev [ \-o " offset " ] [ " image " [ " root_device " [ " offset " ] ] ]"
.BR "swapdev [ \-o " offset " ] [ " image " [ " swap_device " [ " offset " ] ] ]"
.BR "ramsize [ \-o " offset " ] [ " image " [ " size " [ " offset " ] ] ]"
.BR "vidmode [ \-o " offset " ] [ " image " [ " mode " [ " offset " ] ] ]"
.BR "rootflags [ \-o " offset " ] [ " image " [ " flags " [ " offset " ] ] ]"
.fi
.SH DESCRIPTION
.\" " for emacs hilit19
With no arguments,
.B rdev
outputs an
.I /etc/mtab
line for the current root file system.
With no arguments,
.BR swapdev ", " ramsize ", " vidmode ", and " rootflags
print usage information.
In a bootable image for the Linux kernel, there are several 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:
.nf
.RS
498 Root flags
(500 and 502 Reserved)
504 RAM Disk Size
506 VGA Mode
508 Root Device
(510 Boot Signature)
.RE
.fi
.B rdev
will change these values.
Typical values for the
.I image
parameter, which is a bootable Linux kernel image, might be:
.nf
.RS
/vmlinux
/vmunix
/boot/bzImage-2.4.0
/dev/fd0
/dev/fd1
.RE
.fi
When using the
.BR rdev ", or " swapdev
commands, the
.IR root_device " or " swap_device
parameter might be something like:
.nf
.RS
/dev/hda1
/dev/hdf13
/dev/sda2
/dev/sdc4
/dev/ida/c0d0p1
.RE
.fi
For the
.B ramsize
command, the
.B size
parameter specifies the size of the RAM disk in kilobytes.
For the
.B rootflags
command, the
.B 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
.B flags
is non-zero.
For the
.B vidmode
command, the
.B mode
parameter specifies the video mode:
.nf
.RS
-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
.RE
.fi
If the
.I value
is not specified, the
.I image
will be examined to determine the current settings.
.SH OPTIONS
.TP
.B \-s
Causes
.B rdev
to act like
.BR swapdev .
.TP
.B \-r
Causes
.B rdev
to act like
.BR ramsize .
.TP
.B \-R
Causes
.B rdev
to act like
.BR rootflags .
.TP
.B \-v
Causes
.B rdev
to act like
.BR vidmode .
.TP
.B \-h
Provides help.
.SH BUGS
For historical reasons, there are two methods for specifying alternative
values for the offset.
.sp
The user interface is cumbersome, non-intuitive, and should probably be
re-written from scratch, allowing multiple kernel image parameters to be
changed or examined with a single command.
.sp
If LILO is used,
.B rdev
is no longer needed for setting the root device and the VGA mode, since
these parameters that
.B rdev
modifies can be set from the LILO prompt during a boot. However,
.B rdev
is still needed at this time for setting the RAM disk size. Users are
encouraged to find the LILO documentation for more information, and to use
LILO when booting their systems.
.SH AUTHORS
.nf
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)
.fi
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