path: root/util/nvramtool/cli/nvramtool.8

.\"***************************************************************************\
.\" nvramtool.8
.\"***************************************************************************
.\"  This file is part of nvramtool, a utility for reading/writing coreboot
.\"  parameters and displaying information from the coreboot table.
.\"  For details, see https://www.coreboot.org/nvramtool.
.\"
.\"  Please also read the file DISCLAIMER which is included in this software
.\"  distribution.
.\"
.\"  This program is free software; you can redistribute it and/or modify it
.\"  under the terms of the GNU General Public License (as published by the
.\"  Free Software Foundation) version 2, dated June 1991.
.\"
.\"  This program is distributed in the hope that it will be useful, but
.\"  WITHOUT ANY WARRANTY; without even the IMPLIED WARRANTY OF
.\"  MERCHANTABILITY or FITNESS FOR A PARTICULAR PURPOSE.  See the terms and
.\"  conditions of the GNU General Public License for more details.
.\"***************************************************************************/
.TH NVRAMTOOL 8 "September 2008"
.SH NAME
nvramtool \- read/write coreboot-related information
.SH SYNOPSIS
.B "nvramtool [OPTS] [-n] -r NAME"
.br
.B "nvramtool [OPTS] -e NAME"
.br
.B "nvramtool [OPTS] -a"
.br
.B "nvramtool [OPTS] -w NAME=VALUE"
.br
.B "nvramtool [OPTS] -p INPUT_FILE"
.br
.B "nvramtool [OPTS] -i"
.br
.B "nvramtool [OPTS] -c [VALUE]"
.br
.B "nvramtool [OPTS] -l [ARG]"
.br
.B "nvramtool [OPTS] -d"
.br
.B "nvramtool [OPTS] -Y"
.br
.B "nvramtool [OPTS] -b OUTPUT_FILE"
.br
.B "nvramtool [OPTS] -B INPUT_FILE"
.br
.B "nvramtool [OPTS] -x"
.br
.B "nvramtool [OPTS] -X DUMPFILE"
.br
.B "nvramtool [OPTS] -v"
.br
.B "nvramtool [OPTS] -h"
.SH DESCRIPTION
.B "nvramtool"
is a utility for reading/writing coreboot parameters and displaying
information from the coreboot table.

The coreboot table resides in low physical memory.  It is created at boot
time by coreboot, and contains various system information such as the type
of mainboard in use.  It specifies locations in the CMOS (nonvolatile RAM)
where the coreboot parameters are stored.

This program is intended for (x86-based) systems that use coreboot.  For
information about coreboot, see
.br
https://www.coreboot.org/.
.SH PARAMETERS
.TP
.B "[-n] -r NAME"
Show the value of the coreboot parameter given by
.B "NAME."
If
.B "-n"
is specified, show only the value.  Otherwise show both parameter name and
value.
.TP
.B "-e NAME"
Show all possible values for parameter given by
.B "NAME."
.TP
.B "-a"
Show the names and values for all coreboot parameters.
.TP
.B "-w NAME=VALUE"
Assign
.B "VALUE"
to coreboot parameter given by
.B "NAME."
.TP
.B "-p INPUT_FILE"
Assign values to coreboot parameters according to the contents of
.B "INPUT_FILE."
The format of this file is described below.
.TP
.B "-i"
This is similar to the
.B "-p"
option, except that the contents of the input file are taken from standard
input.
.TP
.B "-c [VALUE]"
If
.B "VALUE"
is present then set the CMOS checksum for the coreboot parameters to
.B "VALUE."
Otherwise, show the checksum value.
.TP
.B "-l [ARG]"
If
.B "ARG"
is present then show information from the coreboot table as specified by
.B "ARG."
Otherwise show all possible values for
.B "ARG."
.TP
.B "-d"
Do a low-level dump of the coreboot table.
.TP
.B "-Y"
Write CMOS layout information to standard output.  If redirected to a file,
the layout information may be used as input for the
.B "'-y LAYOUT_FILE'"
option (see below).
.TP
.B "-b OUTPUT_FILE"
Write the contents of CMOS memory to the binary file
.B "OUTPUT_FILE."
The first 14 bytes of
.B "OUTPUT_FILE"
do not contain actual CMOS data, and are always written as zeros.  This is
because the first 14 bytes of the CMOS area do not contain CMOS memory.  These
bytes are involved with the functioning of the real time clock.
.TP
.B "-B INPUT_FILE"
Read binary data from
.B "INPUT_FILE"
and write the data to CMOS memory.  The first 14 bytes of
.B "INPUT_FILE"
are skipped and data is written to CMOS starting at the 15th byte of the CMOS
area.  This is because the first 14 bytes of the CMOS area do not contain CMOS
memory.  These bytes are involved with the functioning of the real time clock.
.TP
.B "-x"
Show a hex dump of all CMOS data.  The first 14 bytes of the dump do not
contain actual CMOS data, and are always shown as zeros.  This is because the
first 14 bytes of the CMOS area do not contain CMOS memory.  These bytes are
involved with the functioning of the real time clock.
.TP
.B "-X DUMPFILE"
Read binary data from
.B "DUMPFILE"
(presumably a CMOS dumpfile created using the
.B "-b OUTPUT_FILE"
option) and show a hex dump of the data.
.TP
.B "-v"
Show version information for this program.
.TP
.B "-h"
Show a help message for this program.
.SH "OPTIONS"
In all cases above,
.B "[OPTS]"
evaluates to the following:

.B "    [-y LAYOUT_FILE | -t]"

The
.B "'-y LAYOUT_FILE'"
option tells nvramtool to obtain CMOS layout information from the contents of
.B "LAYOUT_FILE."
Likewise, the
.B "'-t'"
option tells nvramtool to obtain CMOS layout information from the CMOS option
table (contained within the coreboot table).  If neither option is
specified, the CMOS option table is used by default.
.B "LAYOUT_FILE"
follows the format of the
.B "cmos.layout"
files provided by coreboot.

If the coreboot installed on your system was built without specifying
.B "CONFIG_HAVE_OPTION_TABLE,"
then the coreboot table will not contain a CMOS option table.  In this case,
the
.B "'-y LAYOUT_FILE'"
option must be used.

These two options are silently ignored when used in combination with other
options (such as
.B "-h,"
for instance) for which they are not applicable.
.SH FILE FORMAT
For the
.B "-p"
option,
.B "INPUT_FILE"
must consist of a sequence of lines such that each line is either a blank
line, a comment, or an assignment.  A blank line consists only of zero or
more whitespace characters (spaces and tabs).  A comment is constructed as
follows:

.B "    [ws]#[text]"

Here,
.B "[ws]"
indicates optional whitespace characters and
.B "[text]"
indicates optional text.  Blank lines and comments are both ignored.  An
assignment is constructed as follows:

.B "    [ws]NAME[ws]=[ws]VALUE[ws]"

Here,
.B "NAME"
is the name of a coreboot parameter and
.B "VALUE"
is the value that will be assigned to
.B "NAME."
.B "VALUE"
is allowed to contain whitespace characters, but it must begin and end with
nonwhitespace characters.  Note that each comment must appear on a line by
itself.  If you attempt to add a comment to the end of an assignment, then the
comment will be interpreted as part of
.B "VALUE."
It is useful to observe that the output produced by both the
.B "-a"
and the
.B "'[-n] NAME'"
options (without
.B "-n"
specified) adheres to this file format.
.SH BUGS
This program does not implement any type of synchronization to ensure that
different processes don't stomp on each other when trying to access the
nonvolatile RAM simultaneously.  Therefore, corruption of the BIOS parameter
values may occur if multiple instances of this program are executed
concurrently.
.SH AUTHORS
David S. Peterson <dsp@llnl.gov> <dave_peterson@pobox.com>
.br
Stefan Reinauer <stepan@coresystems.de>