efivar
—
UEFI environment variable interaction
efivar |
[ -abdDHlLNpRtuw ]
[-n
name ]
[-f
file ]
[--append ]
[--ascii ]
[--attributes ]
[--binary ]
[--delete ]
[--device-path ]
[--fromfile
file ]
[--guid ]
[--hex ]
[--list-guids ]
[--list ]
[--name
name ]
[--no-name ]
[--print ]
[--print-decimal ]
[--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
flag is given. This
behavior is not well understood and is currently unimplemented.
-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
- flag is specified, guids are converted to names if they are known (and
show 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.
-N
--no-name
- Do not display the variable name.
-p
--print
- Print the value of the variable.
-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.