Ext4

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ext4 (Quatrième système de fichier étendu) est un système de fichier open-source et la version la plus récente dee la série des systèmes de fichiers étendus. C'est le système de fichier principal utilisé par de nombreux systèmes linux, pouvant être considéré à raison comme l'un des plus stables et des plus testés dans 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 EB 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.

Installation

Kernel

Activate the following kernel options for ext4 support:

KERNEL Enabling ext4 support

File systems  --->
   <*> The Extended 4 (ext4) filesystem

Support for optional ext4 features:

KERNEL Enabling optional features for ext4

File systems  --->
   [*]   Ext4 POSIX Access Control Lists
   [*]   Ext4 Security Labels
   [ ]   EXT4 debugging support

Ext3

Remarque
A normal ext4 system will not need to enable ext3 or ext2 options. These options are here solely for historical purposes.

Activate the following kernel options for ext3 support:

KERNEL Enabling ext3 support

File systems  --->
   <*> Ext3 journalling file system support

Support for optional ext3 features:

KERNEL Enabling ext3 features

File systems  --->
   [*]   Default to 'data=ordered' in ext3 
   [*]   Ext3 extended attributes
   [*]     Ext3 POSIX Access Control Lists
   [*]     Ext3 Security Labels

Ext2

Remarque
Ext2 does not have journaling, support for this was added in Ext3

Activate the following kernel options for ext2 support:

KERNEL Enabling ext2 support

File systems  --->
   <*> Second extended fs support

Support for optional ext2 features:

KERNEL Enabling ext2

File systems  --->
   [*]   Ext2 extended attributes
   [*]     Ext2 POSIX Access Control Lists
   [*]     Ext2 Security Labels

Remarque
The original ext3 filesystem code was removed from the Linux Kernel with version 4.3, instead the ext4 filesystem code can now 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.
The original ext2 filesystem code remains available.

Remarque
Both ext2 and ext3 file timestamps are affected by the year 2038 problem, while ext4 is Y2k38-safe since 2016, Kernel 4.3.6 and e2fsprogs 1.43.

Large drive support

KERNEL Enabling large drives for x86 kernels

-*- 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)

Data provided by the Gentoo Package Database · Last update: 2024-09-12 18:37 More information about USE flags

Emerge

The sys-fs/e2fsprogs package and should be available as part of the default system set.

root #emerge --ask sys-fs/e2fsprogs

Usage

Creation

Attention !
The mkfs.ext4 command irreversibly destroys any content of the partition it is told to format. Be sure to select the right partition!

To create an ext4 filesystem on the /dev/sda1 partition:

root #mkfs.ext4 /dev/sda1

Mounting

See filesystem.

Utilities

Utilities included in the package consist of:

Utility	Description	Man page
badblocks	A small program for stress testing block devices.	Man page
debugfs	An ext2/ext3/ext4 file system debugger.	Man page
dumpe2fs	A tool to dump ext2/ext3/ext4 filesystem information.	Man page
e2fsck	A tool for checking ext2/ext3/ext4 filesystems.	Man page
e2image	A tool for saving critical ext2/ext3/ext4 filesystem metadata to a file.	Man page
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.	Man page
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.	Man page
mke2fs	The base program for creating ext2/ext3/ext4 filesystems. Creation commands symlink here.	Man page
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.	Man page
tune2fs	Adjust tunable filesystem parameters on ext2/ext3/ext4 filesystems.	Man page

Utility	Description	Man page
chattr	Change file attributes on a Linux filesystem.	Man page
lsattr	List file attributes on a Linux second extended filesystem.	Man page

Utility	Description	Man page
e2freefrag	Report free space fragmentation information.	Man page
e4defrag	An online defragmenter for ext4 filesystem.	Man page
filefrag	Report on file fragmentation.	Man page
mklost+found	Create a lost+found directory on a mounted Linux second extended filesystem.	Man page

External resources

https://ext4.wiki.kernel.org/ - The second, third, and fourth extended file system wiki.
https://bugzilla.kernel.org/show_bug.cgi?id=23732 - The final fix for the Year 2038 problem, only for ext4.

References