efivar
—
UEFI environment variable interaction
efivar |
[-abdDHlLNpqRtuw ] [-n
name] [-f
file] [--append ]
[--ascii ] [--attributes ]
[--binary ] [--delete ]
[--device-path ]
[--fromfile file]
[--guid ] [--hex ]
[--list-guids ] [--list ]
[--load-option ] [--name
name] [--no-name ]
[--print ]
[--print-decimal ]
[--quiet ] [--raw-guid ]
[--utf8 ] [--write ] |
This program manages “Unified Extensible Firmware Interface”
(UEFI) environment variables. UEFI variables have three part: A namespace, a
name and a value. The namespace is a GUID that is self assigned by the group
defining the variables. The name is a Unicode name for the variable. The value
is binary data. All Unicode data is presented to the user as UTF-8.
The following options are available:
-n
name --name
name
- Specify the name of the variable to operate on. The
name argument is the GUID of the variable, followed
by a dash, followed by the UEFI variable name. The GUID may be in numeric
format, or may be one of the well known symbolic name (see
--list-guids
for a complete list).
-f
file --fromfile
file
- When writing or appending to a variable, take the data for the variable's
value from file instead of from the command line.
This flag implies
--write
unless the
--append
or --print
flags
are given. This behavior is not well understood and is currently
unimplemented for writes. When --print
is
specified, the contents of the file are used as the value to print using
any other specified flags. This is used primarily for testing purposes for
more complicated variable decoding.
-a
--append
- Append the specified value to the UEFI variable rather than replacing
it.
-t
attr --attributes
attr
- Specify, in hexadecimal, the attributes for this variable. See section 7.2
(GetVariable subsection, Related Definitions) of the UEFI Specification
for hex values to use.
-A
--ascii
- Display the variable data as modified ascii: All printable characters are
printed, while unprintable characters are rendered as a two-digit
hexadecimal number preceded by a % character.
-b
--binary
- Display the variable data as binary data. Usually will be used with the
-N
or --no-name
flag.
Useful in scripts.
-D
--delete
- Delete the specified variable. May not be used with either the
--write
or the --append
flags. No value may be specified.
-d
--device
--device-path
- Interpret the variables printed as UEFI device paths and print the UEFI
standard string representation.
-g
--guid
- Convert GUIDs to names if they are known (and show them up in
--list-guids
).
-H
--hex
- List variable data as a hex dump.
-L
--list-guids
- Lists the well known GUIDs. The names listed here may be used in place of
the numeric GUID values. These names will replace the numeric GUID values
unless
--raw-guid
flag is specified.
-l
--list
- List all the variables. If the
--print
flag is
also listed, their values will be displayed.
--load-option
- Decode the variable as if it were a UEFI Boot Option, including
information about what device and/or paths the UEFI DevicePaths decode
to.
-N
--no-name
- Do not display the variable name.
-p
--print
- Print the value of the variable.
-q
--quiet
- When an error occurs, exit with a non-zero value without outputting any
error messages. Otherwise, produce the normal output and exit with a zero
status.
-R
--raw-guid
- Do not substitute well known names for GUID numeric values in output.
-u
--utf8
- Treat the value of the variable as UCS2 and convert it to UTF8 and print
the result.
-w
--write
- Write (replace) the variable specified with the value specified from
standard input. No command line option to do this is available since UEFI
variables are binary structures rather than strings.
echo(1)
-n
can be used to specify simple strings.
- name
- Display the name environment variable.
The efivar
program is intended to be compatible (strict
superset) with a program of the same name included in the Red Hat libefivar
package, but the -d
and
--print-decimal
flags are not implemented and never
will be.
The -d
flag is short for
--device-path
.
Appendix A of the UEFI specification has the format for GUIDs. All GUIDs
“Globally Unique Identifiers” have the format described in RFC
4122.
The efivar
utility first appeared in
FreeBSD 11.1.