FAT
文件分配表 (FAT) 文件系统是最初创建为了在MS-DOS(和之后的NT 内核的微软Windows)使用;目前,最新版本的FAT (FAT32) 用于 U 盘。[1] 它已经过渡到了 Linux系统上,并获得 Linux 内核的官方支持。
Although FAT32 lacks many of the features inherent in modern file systems, this filesystem can still be found in modern computers, for example, when using EFI System Partition. In 2006 Microsoft has developed a new version of FAT (exFAT) that is not backward compatible with the previous version. See the exFAT article for more info.
安装
内核
File systems --->
DOS/FAT/NT Filesystems --->
< > MSDOS fs support
<*> VFAT (Windows-95) fs support
(437) Default codepage for FAT
(iso8859-1) Default iocharset for FAT
[ ] Enable FAT UTF-8 option by default
-*- Native language support --->
(iso8859-1) Default NLS Option
<*> Codepage 437 (United States, Canada)
<*> NLS ISO 8859-1 (Latin 1; Western European Languages)
-*- NLS UTF-8
Snippet
CONFIG_FAT_FS=y
CONFIG_MSDOS_FS=y
CONFIG_VFAT_FS=y
CONFIG_FAT_DEFAULT_CODEPAGE=437
CONFIG_FAT_DEFAULT_IOCHARSET="iso8859-1"
When planning on mounting FAT partitions, users may need to specify a codepage=
option with mount. In the example above the codepage for the United States and Canada is used, however other codepages can be enabled a necessary. Optionally, users can also set a default codepage for FAT in the kernel configuration. Be sure each codepage value which is to be used has been enabled in the kernel.
Using the
codepage
option via the mount will override the settings used in the kernel.Avoid setting Default iocharset for fat
to UTF-8; it is not recommended. Instead, pass the utf8=true
option when mounting FAT partitions (this requires CONFIG_NLS_UTF8 to be enabled in the kernel). For further information see mount(8) man page or see the appropriate kernel documentation at /usr/src/linux/Documentation/filesystems/vfat.rst
Emerge
The sys-fs/dosfstools package is needed for FAT userspace utilities:
root #
emerge --ask sys-fs/dosfstools
使用
Formatting
To create an FAT file system, use mkfs.fat:
user $
mkfs.fat
mkfs.fat 4.2 (2021-01-31) No device specified. Usage: mkfs.fat [OPTIONS] TARGET [BLOCKS] Create FAT filesystem in TARGET, which can be a block device or file. Use only up to BLOCKS 1024 byte blocks if specified. With the -C option, file TARGET will be created with a size of 1024 bytes times BLOCKS, which must be specified. Options: -a Disable alignment of data structures -A Toggle Atari variant of the filesystem -b SECTOR Select SECTOR as location of the FAT32 backup boot sector -c Check device for bad blocks before creating the filesystem -C Create file TARGET then create filesystem in it -D NUMBER Write BIOS drive number NUMBER to boot sector -f COUNT Create COUNT file allocation tables -F SIZE Select FAT size SIZE (12, 16 or 32) -g GEOM Select disk geometry: heads/sectors_per_track -h NUMBER Write hidden sectors NUMBER to boot sector -i VOLID Set volume ID to VOLID (a 32 bit hexadecimal number) -I Ignore and disable safety checks -l FILENAME Read bad blocks list from FILENAME -m FILENAME Replace default error message in boot block with contents of FILENAME -M TYPE Set media type in boot sector to TYPE --mbr[=y|n|a] Fill (fake) MBR table with one partition which spans whole disk -n LABEL Set volume name to LABEL (up to 11 characters long) --codepage=N use DOS codepage N to encode label (default: 850) -r COUNT Make room for at least COUNT entries in the root directory -R COUNT Set minimal number of reserved sectors to COUNT -s COUNT Set number of sectors per cluster to COUNT -S SIZE Select a sector size of SIZE (a power of two, at least 512) -v Verbose execution --variant=TYPE Select variant TYPE of filesystem (standard or Atari) --invariant Use constants for randomly generated or time based values --offset=SECTOR Write the filesystem at a specific sector into the device file. --help Show this help message and exit
To format /dev/sdx9 partition with the FAT32 filesystem with label "ESP" with verbose output.
root #
mkfs.fat -v -F 32 -n "ESP" /dev/sdx9
It should be possible to mount FAT filesystems with the mount command. Resizing could be done using sys-fs/fatresize.
Case sensitivity
In the original FAT file system only short filenames (8.3 or SFN) are possible, and they are being stored in all upper case only. The systems using the original FAT file system were not case-sensitive (like MS-DOS). As extension to FAT, VFAT not only allows long filenames (LFN) but also lower case letters in filenames. VFAT is case-preserving, but for compatibility reasons existing operating systems (such as Microsoft Windows 95 and Windows NT) were still treating filenames case-insensitive. On the other hand, Unix traditionally was strictly case-sensitive.
In Linux vfat
defaults to treating names case-insensitive (mount option check=r
for relaxed). VFAT can, however, also be mounted with strict case-checking, mount option check=s
, but this can cause problems.
Manual mount options
Using anything other than the default options will cause problems! You have been warned! See section Problem cases for details.
For short names of directories and files (8.3, i.e. "short filenames" or SFN) the behavior of how the name is stored in the filesystem and how it is displayed can be changed using mount option shortname
, which defaults to mixed
since Linux kernel 2.6.32 (December 2009).[2]
file system | mount option | display short name | short name example | store long name | long name example |
FAT12 FAT16 FAT32 VFAT |
FILENAME.EXT
|
– | |||
shortname=lower
|
always forced to lower case | filename.ext
|
when the short name is not all upper case | – | |
shortname=win95
|
upper case | FILENAME.EXT
|
when the short name is not all upper case | – | |
shortname=winnt
|
as is (original) | FILENAME.EXT
|
when the short name is not all lower case or all upper case | – | |
shortname=mixed
|
as is (original) | FILENAME.EXT
|
when the short name is not all upper case | – | |
VFAT | FILENA~1.EXT
|
FileName.Ext
| |||
shortname=lower
|
always forced to lower case | – | when the short name is not all upper case | FileName.Ext
| |
shortname=win95
|
upper case | – | when the short name is not all upper case | FileName.Ext
| |
shortname=winnt
|
as is (original) | – | when the short name is not all lower case or all upper case | FileName.Ext
| |
shortname=mixed
|
as is (original) | – | when the short name is not all upper case | FileName.Ext
| |
VFAT | LONGNA~1.EXT
|
long name.ext
| |||
shortname=lower
|
always forced to lower case | – | when the short name is not all upper case | long name.ext
| |
shortname=win95
|
upper case | – | when the short name is not all upper case | long name.ext
| |
shortname=winnt
|
as is (original) | – | when the short name is not all lower case or all upper case | long name.ext
| |
shortname=mixed
|
as is (original) | – | when the short name is not all upper case | long name.ext
|
A special case is an all lower case short filename, e.g. filename.ext
. If it is created with shortname=winnt
, no LFN VFAT entry will be created.
file system | mount option | store long name | long name example | display short name | short name example |
VFAT | filename.ext
|
→ | FILENAME.EXT
| ||
shortname=winnt
|
when the short name is not all lower case or all upper case | – | as is (short name) | FILENAME.EXT
| |
shortname=lower
|
– | – | always forced to lower case | filename.ext
| |
shortname=win95
|
– | – | upper case | FILENAME.EXT
| |
shortname=mixed
|
– | – | as is | FILENAME.EXT
|
If the file is created with shortname=lower|win95|mixed
however, there will be a VFAT entry (LFN) and a short filename as well, e.g. FILENA~2.EXT
. Whenever there is an LFN, VFAT will display the LFN, not the SFN. This is particularly tricky since the LFN entry might look like an 8.3 SFN, as in the example filename.ext
.
file system | mount option | long name example | display short name | short name example |
VFAT | filename.ext
|
FILENA~2.EXT
| ||
shortname=lower
|
filename.ext
|
lower case | – | |
shortname=win95
|
filename.ext
|
upper case | – | |
shortname=winnt
|
filename.ext
|
as is | – | |
shortname=mixed
|
filename.ext
|
as is | ~ |
Problem cases
With the default settings existing file systems will just work.[3] Firstly, VFAT currently defaults to relaxed case-checking (mount option check=r
). This means that names for directories and files below the mount point will always work as long as they otherwise match in any possible combination of upper and lower case spelling, e.g. filename.ext
will be found even when e.g. FILENAME.EXT
or FileName.Ext
is actually present, because the difference is only in case.
And secondly, short names (8.3, SFN) that are not all upper case will get an additional long filename entry to store the case correctly i.e. making VFAT case-preserving (mount option shortname=mixed
).
On platforms with UEFI this is especially important for compatibility with existing directories and files on the EFI System Partition (ESP), which is vital for the boot configuration. Systems using FAT and VFAT traditionally haven't been case-sensitive, hence it is to be expected that existing directories and filenames differ slightly in their use of upper and lower case letters. With the default settings for
vfat
, Linux is adapting to this convention and treats the whole mount point case-insensitive as well, i.e. /efi/EFI/boot/bootx64.efi (assuming the ESP is mounted under /efi) and other EFI bootloader paths will always work as expected.If only Linux is installed and all file references remain exactly the same, everything should also work with strict case-checking (mount option check=s
). However, since the VFAT file system stores two filenames in some but not all cases, one short (8.3, SFN) and one long name (LFN), conventions regarding the management of those names can cause additional problems. The obvious example is the use of shortname=winnt
, which will convert a short filename in all lower case to a standard FAT filename in all upper case, and skip creating an LFN counterpart. For example, the filename bootx64.efi
would be stored as traditional 8.3 short filename (SFN) BOOTX64.EFI
only. Additionally, shortname=winnt
will display short filenames as is, so the originally written bootx64.efi
doesn't exist, and together with strict case-checking this will cause big problems under Linux.
故障排除
Slow file transfer speeds
If file transfer speeds are slow (can be viewed using iotop), ensure the filesystem is mounted with the async
filesystem option. Edit /etc/fstab (or /etc/autofs/auto.misc when using autofs) system files as needed, likely removing the sync
mount option. By default, filesystems are mounted using the async
mount option.
The filesystem
sync
mount option inhibits slower transfer speeds than the default async
mount option.
The sync
mount option may cause flash media life-cycle shortening also! See man mount option sync
explanation.If file transfer speeds are still slow, try remounting the filesystem with the flush
mount option:
root #
mount -o remount,flush /path/to/mountpoint
Alternative operating system compatible filesystems
Try UDF filesystem using UDFTools, requiring sys-fs/udftools and Linux kernel UDF filesystem driver. Recently code was added to mkudffs for a fix for creating a mock partition increasing compatibility with Microsoft related operating systems. If using an older Linux kernel, ensure block size is set to 512 for increased compatibility. Most options are now default for compatibility, except for the required --bootarea=mbr
creating the mock partition.
root #
mkudffs --bootarea=mbr --label=your_label /dev/device_file
Try Samsung's F2FS filesystem.
UTF-8/UTF-16 character hardware bugs
Sometimes hardware firmware bugs will occur on embedded devices (eg. car radios) when reading their required formatted FAT/FAT32 filesystems containing UTF-8 characters. A workaround is to ensure initially mounting the FAT filesystem using (current default) mount options codepage=437,iocharset=iso8859-1,shortname=mixed,errors=remount-ro
.
For short filenames, codepage=437
is IBM-PC characters or basically ASCII. For long filenames, iocharset=iso8859-1
specifies ASCII. The option shortname=mixed
is default, and can also try shortname=win95
option. Of which, are all current defaults. Additionally to further remedy UTF-8/UTF-16 incompatible characters, use a loop with sed to replace all incompatible UTF-8/UTF-16 characters with an underscore or other ASCII character. (See this replace_chars.sh script.)
For reference, this bug was encountered with a Sony car radio. The MEX-GS610BT radio model would hard reset upon attempting to read a USB flash media/drive containing UTF-8/UTF-16 characters.
As mentioned previously, see /usr/src/linux/Documentation/filesystems/vfat.txt, the Linux Kernel vfat source code documentation, for further explanation on whether to use codepage, iocharset, or utf8 mount options.
Unsorted files and folders
When writing files to the FAT/FAT32 filesystem, devices used for reading the filesystem may show the files and folders as unsorted. Commonly, viewer prefer seeing files and folders sorted alphabetically. Install sys-fs/fatsort, and issue the following command:
root #
fatsort /dev/device_file
另请参阅
- ExFAT — a Microsoft file system optimized for flash memory storage
- ext4 — 一个开源的磁盘文件系统并且是扩展系列文件系统的最新版本。
- btrfs — 一个写入时复制(CoW) 的 Linux 文件系统 ,旨在实现高级功能的同时专注于容错、修复和易于管理等功能。
- removable media — any media that is easily removed from a system.
- /etc/fstab — 定义主要的文件系统在哪里以及如何挂载它们(特别是在启动时)的配置文件。
外部资源
- /usr/src/linux/Documentation/filesystems/vfat.txt - Documentation on the VFAT filesystem included with the Linux kernel sources.
- FAT filesystem and Linux - from Wikipedia