.\" -*- nroff -*-

.\" Copyright 1993, 1994, 1995 by Theodore Ts'o.  All Rights Reserved.

.\" This file may be copied under the terms of the GNU Public License.

.\"

.TH EXT4 5 "@E2FSPROGS_MONTH@ @E2FSPROGS_YEAR@" "E2fsprogs version @E2FSPROGS_VERSION@"

.SH NAME

ext2 \- the second extended file system

.br

ext3 \- the third extended file system

.br

ext4 \- the fourth extended file system

.SH DESCRIPTION

The second, third, and fourth extended file systems, or ext2, ext3, and

ext4 as they are commonly known, are Linux file systems that have

historically been the default file system for many Linux distributions.

They are general purpose file systems that have been designed for

extensibility and backwards compatibility.  In particular, file systems

previously intended for use with the ext2 and ext3 file systems can be

mounted using the ext4 file system driver, and indeed in many modern

Linux distributions, the ext4 file system driver has been configured

to handle mount requests for ext2 and ext3 file systems.

.SH RED HAT ENTERPRISE LINUX 8

The Ext4 file system is fully supported by Red Hat when using default

mke2fs and mount options. In addition, the following non-default mke2fs

features and mount options are also fully supported.

.SH "Non-default features:"

project

.br

quota

.br

mmp

.br

.SH "Non-default mount options:"

bsddf|minixdf

.br

grpid|bsdgroups and nogrpid|sysvgroups

.br

resgid=n and resuid=n

.br

errors={continue|remount-ro|panic}

.br

commit=nrsec

.br

max_batch_time=usec

.br

min_batch_time=usec

.br

grpquota|noquota|quota|usrquota

.br

prjquota

.br

dax

.br

lazytime|nolazytime

.br

discard|nodiscard

.br

init_itable|noinit_itable

.br

jqfmt={vfsold|vfsv0|vfsv1}

.br

usrjquota=aquota.user|grpjquota=aquota.group

.PP

For more information on features and mount options, see the

.BR ext4

man page. Ext4 features and mount options not listed above may not be

fully supported by Red Hat.  If your workload requires a feature or mount

option that is not fully in this Red Hat release, contact Red Hat support

to evaluate it for inclusion in our supported list.

.SH FILE SYSTEM FEATURES

A file system formatted for ext2, ext3, or ext4 can have some

collection of the following file system feature flags enabled.  Some of

these features are not supported by all implementations of the ext2,

ext3, and ext4 file system drivers, depending on Linux kernel version in

use.  On other operating systems, such as the GNU/HURD or FreeBSD, only

a very restrictive set of file system features may be supported in their

implementations of ext2.

.TP

.B 64bit

.br

Enables the file system to be larger than 2^32 blocks.  This feature is set

automatically, as needed, but it can be useful to specify this feature

explicitly if the file system might need to be resized larger than 2^32

blocks, even if it was smaller than that threshold when it was

originally created.  Note that some older kernels and older versions

of e2fsprogs will not support file systems with this ext4 feature enabled.

.TP

.B bigalloc

.br

This ext4 feature enables clustered block allocation, so that the unit of

allocation is a power of two number of blocks.  That is, each bit in the

what had traditionally been known as the block allocation bitmap now

indicates whether a cluster is in use or not, where a cluster is by

default composed of 16 blocks.  This feature can decrease the time

spent on doing block allocation and brings smaller fragmentation, especially

for large files.  The size can be specified using the

.B mke2fs \-C

option.

.IP

.B Warning:

The bigalloc feature is still under development, and may not be fully

supported with your kernel or may have various bugs.  Please see the web

page http://ext4.wiki.kernel.org/index.php/Bigalloc for details.

May clash with delayed allocation (see

.B nodelalloc

mount option).

.IP

This feature requires that the

.B extent

feature be enabled.

.TP

.B casefold

.br

This ext4 feature provides file system level character encoding support

for directories with the casefold (+F) flag enabled.  This feature is

name-preserving on the disk, but it allows applications to lookup for a

file in the file system using an encoding equivalent version of the file

name.

.TP

.B dir_index

.br

Use hashed b-trees to speed up name lookups in large directories.  This

feature is supported by ext3 and ext4 file systems, and is ignored by

ext2 file systems.

.TP

.B dir_nlink

.br

Normally, ext4 allows an inode to have no more than 65,000 hard links.

This applies to regular files as well as directories, which means that

there can be no more than 64,998 subdirectories in a directory (because

each of the '.' and '..' entries, as well as the directory entry for the

directory in its parent directory counts as a hard link).  This feature

lifts this limit by causing ext4 to use a link count of 1 to indicate

that the number of hard links to a directory is not known when the link

count might exceed the maximum count limit.

.TP

.B ea_inode

.br

Normally, a file's extended attributes and associated metadata must fit within

the inode or the inode's associated extended attribute block. This feature

allows the value of each extended attribute to be placed in the data blocks of a

separate inode if necessary, increasing the limit on the size and number of

extended attributes per file.

.TP

.B encrypt

.br

Enables support for file-system level encryption of data blocks and file

names.  The inode metadata (timestamps, file size, user/group ownership,

etc.) is

.I not

encrypted.

.IP

This feature is most useful on file systems with multiple users, or

where not all files should be encrypted.  In many use cases, especially

on single-user systems, encryption at the block device layer using

dm-crypt may provide much better security.

.TP

.B ext_attr

.br

This feature enables the use of extended attributes.  This feature is

supported by ext2, ext3, and ext4.

.TP

.B extent

.br

This ext4 feature allows the mapping of logical block numbers for a

particular inode to physical blocks on the storage device to be stored

using an extent tree, which is a more efficient data structure than the

traditional indirect block scheme used by the ext2 and ext3 file

systems.  The use of the extent tree decreases metadata block overhead,

improves file system performance, and decreases the needed to run

.BR e2fsck (8)

on the file system.

(Note: both

.B extent

and

.B extents

are accepted as valid names for this feature for

historical/backwards compatibility reasons.)

.TP

.B extra_isize

.br

This ext4 feature reserves a specific amount of space in each inode for

extended metadata such as nanosecond timestamps and file creation time,

even if the current kernel does not currently need to reserve this much

space.  Without this feature, the kernel will reserve the amount of

space for features it currently needs, and the rest may be

consumed by extended attributes.

For this feature to be useful the inode size must be 256 bytes in size

or larger.

.TP

.B filetype

.br

This feature enables the storage of file type information in directory

entries.  This feature is supported by ext2, ext3, and ext4.

.TP

.B flex_bg

.br

This ext4 feature allows the per-block group metadata (allocation

bitmaps

and inode tables)

to be placed anywhere on the storage media.  In addition,

.B mke2fs

will place the per-block group metadata together starting at the first

block group of each "flex_bg group".   The size of the flex_bg group

can be specified using the

.B \-G

option.

.TP

.B has_journal

.br

Create a journal to ensure filesystem consistency even across unclean

shutdowns.  Setting the filesystem feature is equivalent to using the

.B \-j

option with

.BR mke2fs " or " tune2fs.

This feature is supported by ext3 and ext4, and ignored by the

ext2 file system driver.

.TP

.B huge_file

.br

This ext4 feature allows files to be larger than 2 terabytes in size.

.TP

.B inline_data

Allow data to be stored in the inode and extended attribute area.

.TP

.B journal_dev

.br

This feature is enabled on the superblock found on an external journal

device.  The block size for the external journal must be the same as the

file system which uses it.

.IP

The external journal device can be used by a file system by specifying

the

.B \-J

.BR device= <external-device>

option to

.BR mke2fs (8)

or

.BR tune2fs(8) .

.TP

.B large_dir

.br

This feature increases the limit on the number of files per directory by

raising the maximum size of directories and, for hashed b-tree directories (see

.BR dir_index ),

the maximum height of the hashed b-tree used to store the directory entries.

.TP

.B large_file

.br

This feature flag is set automatically by modern kernels when a file

larger than 2 gigabytes is created.  Very old kernels could not

handle large files, so this feature flag was used to prohibit those

kernels from mounting file systems that they could not understand.

.TP

.B metadata_csum

.br

This ext4 feature enables metadata checksumming.  This feature stores

checksums for all of the filesystem metadata (superblock, group

descriptor blocks, inode and block bitmaps, directories, and

extent tree blocks).  The checksum algorithm used for the metadata

blocks is different than the one used for group descriptors with the

.B uninit_bg

feature.  These two features are incompatible and

.B metadata_csum

will be used preferentially instead of

.BR uninit_bg .

.TP

.B metadata_csum_seed

.br

This feature allows the filesystem to store the metadata checksum seed in the

superblock, which allows the administrator to change the UUID of a filesystem

using the

.B metadata_csum

feature while it is mounted.

.TP

.B meta_bg

.br

This ext4 feature allows file systems to be resized on-line without explicitly

needing to reserve space for growth in the size of the block group

descriptors.  This scheme is also used to resize file systems which are

larger than 2^32 blocks.  It is not recommended that this feature be set

when a file system is created, since this alternate method of storing

the block group descriptors will slow down the time needed to mount the

file system, and newer kernels can automatically set this feature as

necessary when doing an online resize and no more reserved space is

available in the resize inode.

.TP

.B mmp

.br

This ext4 feature provides multiple mount protection (MMP).  MMP helps to

protect the filesystem from being multiply mounted and is useful in

shared storage environments.

.TP

.B project

.br

This ext4 feature provides project quota support. With this feature,

the project ID of inode will be managed when the filesystem is mounted.

.TP

.B quota

.br

Create quota inodes (inode #3 for userquota and inode

#4 for group quota) and set them in the superblock.

With this feature, the quotas will be enabled

automatically when the filesystem is mounted.

.IP

Causes the quota files (i.e., user.quota and

group.quota which existed

in the older quota design) to be hidden inodes.

.TP

.B resize_inode

.br

This file system feature indicates that space has been reserved so that

the block group descriptor table can be extended while resizing a mounted

file system.  The online resize operation

is carried out by the kernel, triggered by

.BR resize2fs (8).

By default

.B mke2fs

will attempt to reserve enough space so that the

filesystem may grow to 1024 times its initial size.  This can be changed

using the

.B resize

extended option.

.IP

This feature requires that the

.B sparse_super

or

.B sparse_super2

feature be enabled.

.TP

.B sparse_super

.br

This file system feature is set on all modern ext2, ext3, and ext4 file

systems.  It indicates that backup copies of the superblock and block

group descriptors are present only in a few block groups, not all of

them.

.TP

.B sparse_super2

.br

This feature indicates that there will only be at most two backup

superblocks and block group descriptors.  The block groups used to store

the backup superblock(s) and blockgroup descriptor(s) are stored in the

superblock, but typically, one will be located at the beginning of block

group #1, and one in the last block group in the file system.  This

feature is essentially a more extreme version of sparse_super and is

designed to allow a much larger percentage of the disk to have

contiguous blocks available for data files.

.TP

.B uninit_bg

.br

This ext4 file system feature indicates that the block group descriptors

will be protected using checksums, making it safe for

.BR mke2fs (8)

to create a file system without initializing all of the block groups.

The kernel will keep a high watermark of unused inodes, and initialize

inode tables and blocks lazily.  This feature speeds up the time to check

the file system using

.BR e2fsck (8),

and it also speeds up the time required for

.BR mke2fs (8)

to create the file system.

.TP

.B verity

.br

Enables support for verity protected files.  Verity files are readonly,

and their data is transparently verified against a Merkle tree hidden

past the end of the file.  Using the Merkle tree's root hash, a verity

file can be efficiently authenticated, independent of the file's size.

.IP

This feature is most useful for authenticating important read-only files

on read-write file systems.  If the file system itself is read-only,

then using dm-verity to authenticate the entire block device may provide

much better security.

.SH MOUNT OPTIONS

This section describes mount options which are specific to ext2, ext3,

and ext4.  Other generic mount options may be used as well; see

.BR mount (8)

for details.

.SH "Mount options for ext2"

The `ext2' filesystem is the standard Linux filesystem.

Since Linux 2.5.46, for most mount options the default

is determined by the filesystem superblock. Set them with

.BR tune2fs (8).

.TP

.BR acl | noacl

Support POSIX Access Control Lists (or not).  See the

.BR acl (5)

manual page.

.TP

.BR bsddf | minixdf

Set the behavior for the

.I statfs

system call. The

.B minixdf

behavior is to return in the

.I f_blocks

field the total number of blocks of the filesystem, while the

.B bsddf

behavior (which is the default) is to subtract the overhead blocks

used by the ext2 filesystem and not available for file storage. Thus

.sp 1

% mount /k \-o minixdf; df /k; umount /k

.TS

tab(#);

l2 l2 r2 l2 l2 l

l c r c c l.

Filesystem#1024-blocks#Used#Available#Capacity#Mounted on

/dev/sda6#2630655#86954#2412169#3%#/k

.TE

.sp 1

% mount /k \-o bsddf; df /k; umount /k

.TS

tab(#);

l2 l2 r2 l2 l2 l

l c r c c l.

Filesystem#1024-blocks#Used#Available#Capacity#Mounted on

/dev/sda6#2543714#13#2412169#0%#/k

.TE

.sp 1

(Note that this example shows that one can add command line options

to the options given in

.IR /etc/fstab .)

.TP

.BR check=none " or " nocheck

No checking is done at mount time. This is the default. This is fast.

It is wise to invoke

.BR e2fsck (8)

every now and then, e.g.\& at boot time. The non-default behavior is unsupported

(check=normal and check=strict options have been removed). Note that these mount options

don't have to be supported if ext4 kernel driver is used for ext2 and ext3 filesystems.

.TP

.B debug

Print debugging info upon each (re)mount.

.TP

.BR errors= { continue | remount-ro | panic }

Define the behavior when an error is encountered.

(Either ignore errors and just mark the filesystem erroneous and continue,

or remount the filesystem read-only, or panic and halt the system.)

The default is set in the filesystem superblock, and can be

changed using

.BR tune2fs (8).

.TP

.BR grpid | bsdgroups " and " nogrpid | sysvgroups

These options define what group id a newly created file gets.

When

.B grpid

is set, it takes the group id of the directory in which it is created;

otherwise (the default) it takes the fsgid of the current process, unless

the directory has the setgid bit set, in which case it takes the gid

from the parent directory, and also gets the setgid bit set

if it is a directory itself.

.TP

.BR grpquota | noquota | quota | usrquota

The usrquota (same as quota) mount option enables user quota support on the

filesystem. grpquota enables group quotas support. You need the quota utilities

to actually enable and manage the quota system.

.TP

.B nouid32

Disables 32-bit UIDs and GIDs.  This is for interoperability with older

kernels which only store and expect 16-bit values.

.TP

.BR oldalloc " or " orlov

Use old allocator or Orlov allocator for new inodes. Orlov is default.

.TP

\fBresgid=\fP\,\fIn\fP and \fBresuid=\fP\,\fIn\fP

The ext2 filesystem reserves a certain percentage of the available

space (by default 5%, see

.BR mke2fs (8)

and

.BR tune2fs (8)).

These options determine who can use the reserved blocks.

(Roughly: whoever has the specified uid, or belongs to the specified group.)

.TP

.BI sb= n

Instead of using the normal superblock, use an alternative superblock

specified by

.IR n .

This option is normally used when the primary superblock has been

corrupted.  The location of backup superblocks is dependent on the

filesystem's blocksize, the number of blocks per group, and features

such as

.BR sparse_super .

.IP

Additional backup superblocks can be determined by using the

.B mke2fs

program using the

.B \-n

option to print out where the superblocks exist, supposing

.B mke2fs

is supplied with arguments that are consistent with the filesystem's layout

(e.g. blocksize, blocks per group,

.BR sparse_super ,

etc.).

.IP

The block number here uses 1\ k units. Thus, if you want to use logical

block 32768 on a filesystem with 4\ k blocks, use "sb=131072".

.TP

.BR user_xattr | nouser_xattr

Support "user." extended attributes (or not).

.SH "Mount options for ext3"

The ext3 filesystem is a version of the ext2 filesystem which has been

enhanced with journaling.  It supports the same options as ext2 as

well as the following additions:

.TP

.BR journal_dev=devnum / journal_path=path

When the external journal device's major/minor numbers

have changed, these options allow the user to specify

the new journal location.  The journal device is

identified either through its new major/minor numbers encoded

in devnum, or via a path to the device.

.TP

.BR norecovery / noload

Don't load the journal on mounting.  Note that

if the filesystem was not unmounted cleanly,

skipping the journal replay will lead to the

filesystem containing inconsistencies that can

lead to any number of problems.

.TP

.BR data= { journal | ordered | writeback }

Specifies the journaling mode for file data.  Metadata is always journaled.

To use modes other than

.B ordered

on the root filesystem, pass the mode to the kernel as boot parameter, e.g.\&

.IR rootflags=data=journal .

.RS

.TP

.B journal

All data is committed into the journal prior to being written into the

main filesystem.

.TP

.B ordered

This is the default mode.  All data is forced directly out to the main file

system prior to its metadata being committed to the journal.

.TP

.B writeback

Data ordering is not preserved \(en data may be written into the main

filesystem after its metadata has been committed to the journal.

This is rumoured to be the highest-throughput option.  It guarantees

internal filesystem integrity, however it can allow old data to appear

in files after a crash and journal recovery.

.RE

.TP

.B data_err=ignore

Just print an error message if an error occurs in a file data buffer in

ordered mode.

.TP

.B data_err=abort

Abort the journal if an error occurs in a file data buffer in ordered mode.

.TP

.BR barrier=0 " / " barrier=1 "

This disables / enables the use of write barriers in the jbd code.  barrier=0

disables, barrier=1 enables (default). This also requires an IO stack which can

support barriers, and if jbd gets an error on a barrier write, it will disable

barriers again with a warning.  Write barriers enforce proper on-disk ordering

of journal commits, making volatile disk write caches safe to use, at some

performance penalty.  If your disks are battery-backed in one way or another,

disabling barriers may safely improve performance.

.TP

.BI commit= nrsec

Start a journal commit every

.I nrsec

seconds.  The default value is 5 seconds.  Zero means default.

.TP

.B user_xattr

Enable Extended User Attributes. See the

.BR attr (5)

manual page.

.TP

.BR jqfmt= { vfsold | vfsv0 | vfsv1 }

Apart from the old quota system (as in ext2, jqfmt=vfsold aka version 1 quota)

ext3 also supports journaled quotas (version 2 quota). jqfmt=vfsv0 or

jqfmt=vfsv1 enables journaled quotas. Journaled quotas have the advantage that

even after a crash no quota check is required. When the

.B quota

filesystem feature is enabled, journaled quotas are used automatically, and

this mount option is ignored.

.TP

.BR usrjquota=aquota.user | grpjquota=aquota.group

For journaled quotas (jqfmt=vfsv0 or jqfmt=vfsv1), the mount options

usrjquota=aquota.user and grpjquota=aquota.group are required to tell the

quota system which quota database files to use. When the

.B quota

filesystem feature is enabled, journaled quotas are used automatically, and

this mount option is ignored.

.SH "Mount options for ext4"

The ext4 filesystem is an advanced level of the ext3 filesystem which

incorporates scalability and reliability enhancements for supporting large

filesystem.

The options

.B journal_dev, journal_path, norecovery, noload, data, commit, orlov,

.B oldalloc, [no]user_xattr, [no]acl, bsddf, minixdf, debug, errors,

.B data_err, grpid, bsdgroups, nogrpid, sysvgroups, resgid, resuid, sb,

.B quota, noquota, nouid32, grpquota, usrquota, usrjquota, grpjquota,

.B and jqfmt are backwardly compatible with ext3 or ext2.

.TP

.B journal_checksum | nojournal_checksum

The journal_checksum option enables checksumming of the journal transactions.

This will allow the recovery code in e2fsck and the kernel to detect corruption

in the kernel. It is a compatible change and will be ignored by older kernels.

.TP

.B journal_async_commit

Commit block can be written to disk without waiting for descriptor blocks. If

enabled older kernels cannot mount the device.

This will enable 'journal_checksum' internally.

.TP

.BR barrier=0 " / " barrier=1 " / " barrier " / " nobarrier

These mount options have the same effect as in ext3.  The mount options

"barrier" and "nobarrier" are added for consistency with other ext4 mount

options.

The ext4 filesystem enables write barriers by default.

.TP

.BI inode_readahead_blks= n

This tuning parameter controls the maximum number of inode table blocks that

ext4's inode table readahead algorithm will pre-read into the buffer cache.

The value must be a power of 2. The default value is 32 blocks.

.TP

.BI stripe= n

Number of filesystem blocks that mballoc will try to use for allocation size

and alignment. For RAID5/6 systems this should be the number of data disks *

RAID chunk size in filesystem blocks.

.TP

.B delalloc

Deferring block allocation until write-out time.

.TP

.B nodelalloc

Disable delayed allocation. Blocks are allocated when data is copied from user

to page cache.

.TP

.BI max_batch_time= usec

Maximum amount of time ext4 should wait for additional filesystem operations to

be batch together with a synchronous write operation. Since a synchronous

write operation is going to force a commit and then a wait for the I/O

complete, it doesn't cost much, and can be a huge throughput win, we wait for a

small amount of time to see if any other transactions can piggyback on the

synchronous write. The algorithm used is designed to automatically tune for

the speed of the disk, by measuring the amount of time (on average) that it

takes to finish committing a transaction. Call this time the "commit time".

If the time that the transaction has been running is less than the commit time,

ext4 will try sleeping for the commit time to see if other operations will join

the transaction. The commit time is capped by the max_batch_time, which

defaults to 15000\ \[mc]s (15\ ms). This optimization can be turned off entirely by

setting max_batch_time to 0.

.TP

.BI min_batch_time= usec

This parameter sets the commit time (as described above) to be at least

min_batch_time. It defaults to zero microseconds. Increasing this parameter

may improve the throughput of multi-threaded, synchronous workloads on very

fast disks, at the cost of increasing latency.

.TP

.BI journal_ioprio= prio

The I/O priority (from 0 to 7, where 0 is the highest priority) which should be

used for I/O operations submitted by kjournald2 during a commit operation.

This defaults to 3, which is a slightly higher priority than the default I/O

priority.

.TP

.B abort

Simulate the effects of calling ext4_abort() for

debugging purposes.  This is normally used while

remounting a filesystem which is already mounted.

.TP

.BR auto_da_alloc | noauto_da_alloc

Many broken applications don't use fsync() when

replacing existing files via patterns such as

fd = open("foo.new")/write(fd,...)/close(fd)/ rename("foo.new", "foo")

or worse yet

fd = open("foo", O_TRUNC)/write(fd,...)/close(fd).

If auto_da_alloc is enabled, ext4 will detect the replace-via-rename and

replace-via-truncate patterns and force that any delayed allocation blocks are

allocated such that at the next journal commit, in the default data=ordered

mode, the data blocks of the new file are forced to disk before the rename()

operation is committed.  This provides roughly the same level of guarantees as

ext3, and avoids the "zero-length" problem that can happen when a system

crashes before the delayed allocation blocks are forced to disk.

.TP

.B noinit_itable

Do not initialize any uninitialized inode table blocks in the background. This

feature may be used by installation CD's so that the install process can

complete as quickly as possible; the inode table initialization process would

then be deferred until the next time the filesystem is mounted.

.TP

.B init_itable=n

The lazy itable init code will wait n times the number of milliseconds it took

to zero out the previous block group's inode table. This minimizes the impact on

system performance while the filesystem's inode table is being initialized.

.TP

.BR discard / nodiscard

Controls whether ext4 should issue discard/TRIM commands to the underlying

block device when blocks are freed.  This is useful for SSD devices and

sparse/thinly-provisioned LUNs, but it is off by default until sufficient

testing has been done.

.TP

.BR block_validity / noblock_validity

This option enables/disables the in-kernel facility for tracking

filesystem metadata blocks within internal data structures. This allows multi-\c

block allocator and other routines to quickly locate extents which might

overlap with filesystem metadata blocks. This option is intended for debugging

purposes and since it negatively affects the performance, it is off by default.

.TP

.BR dioread_lock / dioread_nolock

Controls whether or not ext4 should use the DIO read locking. If the

dioread_nolock option is specified ext4 will allocate uninitialized extent

before buffer write and convert the extent to initialized after IO completes.

This approach allows ext4 code to avoid using inode mutex, which improves

scalability on high speed storages. However this does not work with data

journaling and dioread_nolock option will be ignored with kernel warning.

Note that dioread_nolock code path is only used for extent-based files.

Because of the restrictions this options comprises it is off by default

(e.g.\& dioread_lock).

.TP

.B max_dir_size_kb=n

This limits the size of the directories so that any attempt to expand them

beyond the specified limit in kilobytes will cause an ENOSPC error. This is

useful in memory-constrained environments, where a very large directory can

cause severe performance problems or even provoke the Out Of Memory killer. (For

example, if there is only 512\ MB memory available, a 176\ MB directory may

seriously cramp the system's style.)

.TP

.B i_version

Enable 64-bit inode version support. This option is off by default.

.TP

.B nombcache

This option disables use of mbcache for extended attribute deduplication. On

systems where extended attributes are rarely or never shared between files,

use of mbcache for deduplication adds unnecessary computational overhead.

.TP

.B prjquota

The prjquota mount option enables project quota support on the filesystem.

You need the quota utilities to actually enable and manage the quota system.

This mount option requires the

.B project

filesystem feature.

.SH FILE ATTRIBUTES

The ext2, ext3, and ext4 filesystems support setting the following file

attributes on Linux systems using the

.BR chattr (1)

utility:

.sp

.BR a " - append only"

.sp

.BR A " - no atime updates"

.sp

.BR d " - no dump"

.sp

.BR D " - synchronous directory updates"

.sp

.BR i " - immutable"

.sp

.BR S " - synchronous updates"

.sp

.BR u " - undeletable"

.sp

In addition, the ext3 and ext4 filesystems support the following flag:

.sp

.BR j " - data journaling"

.sp

Finally, the ext4 filesystem also supports the following flag:

.sp

.BR e " - extents format"

.sp

For descriptions of these attribute flags, please refer to the

.BR chattr (1)

man page.

.SH KERNEL SUPPORT

This section lists the file system driver (e.g., ext2, ext3, ext4) and

upstream kernel version where a particular file system feature was

supported.  Note that in some cases the feature was present in earlier

kernel versions, but there were known, serious bugs.  In other cases the

feature may still be considered in an experimental state.  Finally, note

that some distributions may have backported features into older kernels;

in particular the kernel versions in certain "enterprise distributions"

can be extremely misleading.

.IP "\fBfiletype\fR" 2in

ext2, 2.2.0

.IP "\fBsparse_super\fR" 2in

ext2, 2.2.0

.IP "\fBlarge_file\fR" 2in

ext2, 2.2.0

.IP "\fBhas_journal\fR" 2in

ext3, 2.4.15

.IP "\fBext_attr\fR" 2in

ext2/ext3, 2.6.0

.IP "\fBdir_index\fR" 2in

ext3, 2.6.0

.IP "\fBresize_inode\fR" 2in

ext3, 2.6.10 (online resizing)

.IP "\fB64bit\fR" 2in

ext4, 2.6.28

.IP "\fBdir_nlink\fR" 2in

ext4, 2.6.28

.IP "\fBextent\fR" 2in

ext4, 2.6.28

.IP "\fBextra_isize\fR" 2in

ext4, 2.6.28

.IP "\fBflex_bg\fR" 2in

ext4, 2.6.28

.IP "\fBhuge_file\fR" 2in

ext4, 2.6.28

.IP "\fBmeta_bg\fR" 2in

ext4, 2.6.28

.IP "\fBuninit_bg\fR" 2in

ext4, 2.6.28

.IP "\fBmmp\fR" 2in

ext4, 3.0

.IP "\fBbigalloc\fR" 2in

ext4, 3.2

.IP "\fBquota\fR" 2in

ext4, 3.6

.IP "\fBinline_data\fR" 2in

ext4, 3.8

.IP "\fBsparse_super2\fR" 2in

ext4, 3.16

.IP "\fBmetadata_csum\fR" 2in

ext4, 3.18

.IP "\fBencrypt\fR" 2in

ext4, 4.1

.IP "\fBmetadata_csum_seed\fR" 2i

ext4, 4.4

.IP "\fBproject\fR" 2i

ext4, 4.5

.IP "\fBea_inode\fR" 2i

ext4, 4.13

.IP "\fBlarge_dir\fR" 2i

ext4, 4.13

.IP "\fBcasefold\fR" 2i

ext4, 5.2

.IP "\fBverity\fR" 2i

ext4, 5.4

.SH SEE ALSO

.BR mke2fs (8),

.BR mke2fs.conf (5),

.BR e2fsck (8),

.BR dumpe2fs (8),

.BR tune2fs (8),

.BR debugfs (8),

.BR mount (8),

.BR chattr (1)