nvramtool man page
nvramtool — read/write coreboot-related information
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
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
- [-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.
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.
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.
Do a low-level dump of the coreboot table.
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.
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.
Show version information for this program.
Show a help message for this program.
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 CONFIG_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.
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:
Here, [ws] indicates optional whitespace characters and [text] indicates optional text. Blank lines and comments are both ignored. An assignment is constructed as follows:
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.
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.
David S. Peterson <email@example.com> <firstname.lastname@example.org>
Stefan Reinauer <email@example.com>