NAME
nvramtool - read/write coreboot-related information
SYNOPSIS
nvramtool [OPTS] [-n] -r NAME
nvramtool [OPTS] -e NAME
nvramtool [OPTS] -a
nvramtool [OPTS] -w NAME=VALUE
nvramtool [OPTS] -p INPUT_FILE
nvramtool [OPTS] -i
nvramtool [OPTS] -c [VALUE]
nvramtool [OPTS] -l [ARG]
nvramtool [OPTS] -d
nvramtool [OPTS] -Y
nvramtool [OPTS] -b OUTPUT_FILE
nvramtool [OPTS] -B INPUT_FILE
nvramtool [OPTS] -x
nvramtool [OPTS] -X DUMPFILE
nvramtool [OPTS] -v
nvramtool [OPTS] -h
DESCRIPTION
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
http://www.coreboot.org/.
PARAMETERS
[-n] -r NAME
Show the value of the coreboot parameter given by NAME. If -n
is specified, show only the value. Otherwise show both
parameter name and value.
-e NAME
Show all possible values for parameter given by NAME.
-a Show the names and values for all coreboot parameters.
-w NAME=VALUE
Assign VALUE to coreboot parameter given by NAME.
-p INPUT_FILE
Assign values to coreboot parameters according to the contents
of INPUT_FILE. The format of this file is described below.
-i This is similar to the -p option, except that the contents of
the input file are taken from standard input.
-c [VALUE]
If VALUE is present then set the CMOS checksum for the coreboot
parameters to VALUE. Otherwise, show the checksum value.
-l [ARG]
If ARG is present then show information from the coreboot table
as specified by ARG. Otherwise show all possible values for
ARG.
-d Do a low-level dump of the coreboot table.
-Y Write CMOS layout information to standard output. If redirected
to a file, the layout information may be used as input for the
’-y LAYOUT_FILE’ option (see below).
-b OUTPUT_FILE
Write the contents of CMOS memory to the binary file
OUTPUT_FILE. The first 14 bytes of 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.
-B INPUT_FILE
Read binary data from INPUT_FILE and write the data to CMOS
memory. The first 14 bytes of 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.
-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.
-X DUMPFILE
Read binary data from DUMPFILE (presumably a CMOS dumpfile
created using the -b OUTPUT_FILE option) and show a hex dump of
the data.
-v Show version information for this program.
-h Show a help message for this program.
OPTIONS
In all cases above, [OPTS] evaluates to the following:
[-y LAYOUT_FILE | -t]
The ’-y LAYOUT_FILE’ option tells nvramtool to obtain CMOS layout
information from the contents of LAYOUT_FILE. Likewise, the ’-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. LAYOUT_FILE
follows the format of the cmos.layout files provided by coreboot.
If the coreboot installed on your system was built without specifying
HAVE_OPTION_TABLE, then the coreboot table will not contain a CMOS
option table. In this case, the ’-y LAYOUT_FILE’ option must be used.
These two options are silently ignored when used in combination with
other options (such as -h, for instance) for which they are not
applicable.
FILE FORMAT
For the -p option, 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:
[ws]#[text]
Here, [ws] indicates optional whitespace characters and [text]
indicates optional text. Blank lines and comments are both ignored.
An assignment is constructed as follows:
[ws]NAME[ws]=[ws]VALUE[ws]
Here, NAME is the name of a coreboot parameter and VALUE is the value
that will be assigned to NAME. 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 VALUE. It is useful to observe that the output
produced by both the -a and the ’[-n] NAME’ options (without -n
specified) adheres to this file format.
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.
AUTHORS
David S. Peterson <dsp@llnl.gov> <dave_peterson@pobox.com>
Stefan Reinauer <stepan@coresystems.de>