Ext4
ext4 (fourth extended file system, quarto file system esteso) è un open source filesystem e la versione più recente della serie estesa di filesystem. È il file system principale in uso da molti sistemi Linux, rendendolo probabilmente il file system più stabile e ben testato supportato in Linux.
Initially created as a fork of ext3, ext4 brings new features, performance improvements, and removal of size limits with moderate changes to the on-disk format. It can span volumes up to 1 Exabyte and with maximum file size of 16TB. Instead of the classic ext2/3 bitmap block allocation, ext4 uses extents, which improve large file performance and reduce fragmentation. Ext4 also provides more sophisticated block allocation algorithms (delayed allocation and multiblock allocation) giving the filesystem driver more ways to optimize the layout of data on the disk.
Installazione
Kernel
Attivare le seguenti opzioni del kernel per abilitare il supporto ext4:
File systems --->
<*> The Extended 4 (ext4) filesystem
Supporto per funzionalità ext4 opzionali:
File systems --->
[*] Ext4 POSIX Access Control Lists
[*] Ext4 Security Labels
[ ] EXT4 debugging support
The ext4 driver can handle ext2, ext3 and ext4 filesystems. It will maintain compatibility if the filesystem is mounted as ext2 or ext3, and will provide upgradability when mounted as ext4. Additionally tune2fs can be used to add ext3- and ext4-specific features to an existing ext2 or ext3 filesystem, though certain hard limits will remain.
Both ext2 and ext3 file timestamps are affected by the year 2038 problem, while ext4 is Y2k38-safe since 2016, Linux kernel 4.3.6 and e2fsprogs 1.43. When an Extended filesystem specifically without a journal is desired, instead of ext2 a journal-less ext4 filesystem should be used; see ext4 without a journal.
Ext3
The original ext3 driver was removed from the Linux kernel with version 4.3. There should remain only rare cases which make it necessary to use an ext3 filesystem, in which case the ext4 driver may be used.
It is advised to use the ext4 driver to mount ext3 filesystems. The old ext3 driver should not be enabled.
Activate the following kernel options for ext3 driver:
File systems --->
<*> Ext3 journalling file system support
Support for optional ext3 features:
File systems --->
[*] Default to 'data=ordered' in ext3
[*] Ext3 extended attributes
[*] Ext3 POSIX Access Control Lists
[*] Ext3 Security Labels
Ext2
The ext2 filesystem does not have journaling support.
When the original ext2 filesystem driver is enabled, it will be used to mount ext2 filesystems. Under normal circumstances it is highly recommended to use the ext4 driver, and not to enable the older ext2 driver: there is absolutely no necessity for a separate driver when the ext4 driver is already available to mount ext2 filesystems.
The original ext2 driver remains available for special cases. For example: compared to the ext4 driver, the original ext2 code has a lower memory footprint. (In such cases, the ext4 driver will be entirely omitted, so ext3 and ext4 filesystems will not be available.)
Activate the following kernel options for ext2 support using the original ext2 driver:
File systems --->
<*> Second extended fs support
Support for optional ext2 features:
File systems --->
[*] Ext2 extended attributes
[*] Ext2 POSIX Access Control Lists
[*] Ext2 Security Labels
Supporto per unità di grandi dimensioni
-*- Enable the block layer --->
[*] Support for large (2TB+) block devices and files
USE flags
USE flags for sys-fs/e2fsprogs Standard EXT2/EXT3/EXT4 filesystem utilities
+tools
|
Build extfs tools (mke2fs, e2fsck, tune2fs, etc.) |
archive
|
Add support for mke2fs to read a tarball as input. This allows not needing privileges. Needs app-arch/libarchive. |
cron
|
Install e2scrub_all cron script |
fuse
|
Build fuse2fs, a FUSE file system client for ext2/ext3/ext4 file systems |
nls
|
Add Native Language Support (using gettext - GNU locale utilities) |
static-libs
|
Build static versions of dynamic libraries as well |
test
|
Enable dependencies and/or preparations necessary to run tests (usually controlled by FEATURES=test but can be toggled independently) |
verify-sig
|
Verify upstream signatures on distfiles |
Emerge
The sys-fs/e2fsprogs package and should be available as part of the default system set. Despite the historical name, the package includes utilities for ext3 and ext4.
root #emerge --ask sys-fs/e2fsprogsUtilizzo
Creazione
Il comando mkfs.ext4 distrugge irreversibilmente ogni contenuto della partizione che sarà per essere formattata. Assicurati di selezionare la partizione giusta!
Per creare un filesystem ext4 nella partizione /dev/sda1:
root #mkfs.ext4 /dev/sda1Mounting
See filesystem.
Ext4 without a journal
In specific use-cases it may be desirable to create a journal-less filesystem. Even though ext2 does provide exactly that, it is also affected by the year 2038 problem regarding file timestamps. Only the ext4 filesystem has been made Y2K38-safe.
In order to get the current Extended filesystem without a journal, an ext4 filesystem can be created without the has_journal feature, or modified accordingly. (Note that this is not possible on ext3 filesystems.)
Removing the journal from an existing ext4 volume
To display filesystem features currently enabled on a specific ext2/3/4 volume:
root #dumpe2fs -h /dev/sdx5 | grep "^Filesystem features:"To disable the journal, the filesystem must be unmounted first:
root #umount /dev/sdx5 root #tune2fs -O ^has_journal /dev/sdx5The leading ^ disables the specified feature. Otherwise the feature would be enabled; i.e. to enable a journal on an existing ext2 or journal-less ext4 filesystem:
root #tune2fs -O has_journal /dev/sdx5Running dumpe2fs again, the has_journal feature should no longer be listed. The filesystem can now be mounted again:
root #mount /dev/sdx5 Create a new journal-less ext4 volume
To create (i.e. format) a new ext4 volume without a journal, the default options of the ext4 filesystem type have to be overridden:
root #mke2fs -t ext4 -O ^has_journal /dev/sdx5Utilities
Utilities included in the package consist of:
| Utility | Description | Man page |
|---|---|---|
| badblocks | A small program for stress testing block devices. | badblocks(8) |
| debugfs | An ext2/ext3/ext4 file system debugger. | debugfs(8) |
| dumpe2fs | A tool to dump ext2/ext3/ext4 filesystem information. | dumpe2fs(8) |
| e2fsck | A tool for checking ext2/ext3/ext4 filesystems. | e2fsck(8) |
| e2image | A tool for saving critical ext2/ext3/ext4 filesystem metadata to a file. | e2image(8) |
| e2label | A tool to change the label on an ext2/ext3/ext4 filesystem (symlinks to tune2fs). | |
| e2undo | A tool to replay an undo log for an ext2/ext3/ext4 filesystem. | e2undo(8) |
| fsck.ext2 | Checks, specifically, an ext2 filesystem (symlinks to e2fsck). | |
| fsck.ext3 | Checks, specifically, an ext3 filesystem (symlinks to e2fsck). | |
| fsck.ext4 | Checks, specifically, an ext4 filesystem (symlinks to e2fsck). | |
| fsck.ext4dev | Checks, specifically, an ext4dev filesystem (symlinks to e2fsck). | |
| logsave | A tool to save the output of a command in a logfile. | logsave(8) |
| mke2fs | The base program for creating ext2/ext3/ext4 filesystems. Creation commands symlink here. | mke2fs(8) |
| mkfs.ext2 | Creates, specifically, an ext2 filesystem (symlinks to mke2fs). | |
| mkfs.ext3 | Creates, specifically, an ext3 filesystem (symlinks to mke2fs). | |
| mkfs.ext4 | Creates, specifically, an ext4 filesystem (symlinks to mke2fs). | |
| mkfs.ext4dev | Creates, specifically, an ext24dev filesystem (symlinks to mke2fs). | |
| resize2fs | An ext2/ext3/ext4 filesystem resizer. | resize2fs(8) |
| tune2fs | Adjust tunable filesystem parameters on ext2/ext3/ext4 filesystems. | tune2fs(8) |
| chattr | Change file attributes on a Linux filesystem. | chattr(1) |
| lsattr | List ext2/ext3/ext4 file attributes. | lsattr(1) |
| e2freefrag | Report free space fragmentation information. | e2freefrag(8) |
| e4defrag | An online defragmenter for ext4 filesystem. | e4defrag(8) |
| filefrag | Report on file fragmentation. | filefrag(8) |
| mklost+found | Create a lost+found directory on a mounted ext2/ext3/ext4 file system. | mklost+found(8) |
Vedere anche
- Ext4 encryption — provides instructions on encrypting files in a home partition using the ext4 filesystem's built-in file based encryption.
- JFS — un filesystem journaling a 64 bit creato da IBM
- Btrfs — un filesystem CoW (copy-on-write, copia-in-scrittura) adatto a Linux che mira ad implementare funzionalità avanzate, concentrandosi sulla tolleranza agli errori, la riparazione e la facilità di amministrazione.
- XFS — un filesystem journaling ad alte prestazioni
- F2FS — un filesystem progettato per dispositivi basati su flash NAND.