1 .. SPDX-License-Identifier: GPL-2.0 2 3 ======================================= 4 efivarfs - a (U)EFI variable filesystem 5 ======================================= 6 7 The efivarfs filesystem was created to address the shortcomings of 8 using entries in sysfs to maintain EFI variables. The old sysfs EFI 9 variables code only supported variables of up to 1024 bytes. This 10 limitation existed in version 0.99 of the EFI specification, but was 11 removed before any full releases. Since variables can now be larger 12 than a single page, sysfs isn't the best interface for this. 13 14 Variables can be created, deleted and modified with the efivarfs 15 filesystem. 16 17 efivarfs is typically mounted like this:: 18 19 mount -t efivarfs none /sys/firmware/efi/efivars 20 21 Due to the presence of numerous firmware bugs where removing non-standard 22 UEFI variables causes the system firmware to fail to POST, efivarfs 23 files that are not well-known standardized variables are created 24 as immutable files. This doesn't prevent removal - "chattr -i" will work - 25 but it does prevent this kind of failure from being accomplished 26 accidentally. 27 28 .. warning :: 29 When a content of an UEFI variable in /sys/firmware/efi/efivars is 30 displayed, for example using "hexdump", pay attention that the first 31 4 bytes of the output represent the UEFI variable attributes, 32 in little-endian format. 33 34 Practically the output of each efivar is composed of: 35 36 +-----------------------------------+ 37 |4_bytes_of_attributes + efivar_data| 38 +-----------------------------------+ 39 40 *See also:* 41 42 - Documentation/admin-guide/acpi/ssdt-overlays.rst 43 - Documentation/ABI/removed/sysfs-firmware-efi-vars
Linux® is a registered trademark of Linus Torvalds in the United States and other countries.
TOMOYO® is a registered trademark of NTT DATA CORPORATION.