.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
.TP
.B encrypt
.br
-This ext4 feature provides file-system level encryption of data blocks
-and file names. The inode metadata (timestamps, file size, user/group
-ownership, etc.) is
+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
.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
+Create a journal to ensure file system consistency even across unclean
+shutdowns. Setting the file system feature is equivalent to using the
.B \-j
option with
.BR mke2fs " or " tune2fs.
option to
.BR mke2fs (8)
or
-.BR tune2fs(8).
+.BR tune2fs(8) .
.TP
.B large_dir
.br
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 .
-.\" .br
-.\" .B Future feature, available in e2fsprogs 1.43-WIP
+.TP
+.B metadata_csum
+.br
+This ext4 feature enables metadata checksumming. This feature stores
+checksums for all of the file system 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 file system to store the metadata checksum seed in the
+superblock, which allows the administrator to change the UUID of a file system
+using the
+.B metadata_csum
+feature while it is mounted.
.TP
.B meta_bg
.br
.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
+protect the file system from being multiply mounted and is useful in
shared storage environments.
-.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 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.
+the project ID of inode will be managed when the file system 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.
+automatically when the file system 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
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
+file system 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
designed to allow a much larger percentage of the disk to have
contiguous blocks available for data files.
.TP
+.B stable_inodes
+.br
+Marks the file system's inode numbers and UUID as stable.
+.BR resize2fs (8)
+will not allow shrinking a file system with this feature, nor
+will
+.BR tune2fs (8)
+allow changing its UUID. This feature allows the use of specialized encryption
+settings that make use of the inode numbers and UUID. Note that the
+.B encrypt
+feature still needs to be enabled separately.
+.B stable_inodes
+is a "compat" feature, so old kernels will allow it.
+.TP
.B uninit_bg
.br
This ext4 file system feature indicates that the block group descriptors
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.
+The `ext2' file system is the standard Linux file system.
Since Linux 2.5.46, for most mount options the default
-is determined by the filesystem superblock. Set them with
+is determined by the file system superblock. Set them with
.BR tune2fs (8).
.TP
.BR acl | noacl
.B minixdf
behavior is to return in the
.I f_blocks
-field the total number of blocks of the filesystem, while the
+field the total number of blocks of the file system, 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
+used by the ext2 file system 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
+File System#1024-blocks#Used#Available#Capacity#Mounted on
/dev/sda6#2630655#86954#2412169#3%#/k
.TE
.sp 1
tab(#);
l2 l2 r2 l2 l2 l
l c r c c l.
-Filesystem#1024-blocks#Used#Available#Capacity#Mounted on
+File System#1024-blocks#Used#Available#Capacity#Mounted on
/dev/sda6#2543714#13#2412169#0%#/k
.TE
.sp 1
.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.
+don't have to be supported if ext4 kernel driver is used for ext2 and ext3 file systems.
.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
+(Either ignore errors and just mark the file system erroneous and continue,
+or remount the file system read-only, or panic and halt the system.)
+The default is set in the file system superblock, and can be
changed using
.BR tune2fs (8).
.TP
.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
+file system. grpquota enables group quotas support. You need the quota utilities
to actually enable and manage the quota system.
.TP
.B nouid32
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
+The ext2 file system reserves a certain percentage of the available
space (by default 5%, see
.BR mke2fs (8)
and
(Roughly: whoever has the specified uid, or belongs to the specified group.)
.TP
.BI sb= n
-Instead of block 1, use block
-.I n
-as superblock. This could be useful when the filesystem has been damaged.
-(Earlier, copies of the superblock would be made every 8192 blocks: in
-block 1, 8193, 16385, \&...\& (and one got thousands of copies on
-a big filesystem). Since version 1.08,
+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
+file system'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
-has a \-s (sparse superblock) option to reduce the number of backup
-superblocks, and since version 1.15 this is the default. Note
-that this may mean that ext2 filesystems created by a recent
+program using the
+.B \-n
+option to print out where the superblocks exist, supposing
.B mke2fs
-cannot be mounted r/w under Linux 2.0.*.)
+is supplied with arguments that are consistent with the file system'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".
+block 32768 on a file system 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
+The ext3 file system is a version of the ext2 file system which has been
enhanced with journaling. It supports the same options as ext2 as
well as the following additions:
.TP
.TP
.BR norecovery / noload
Don't load the journal on mounting. Note that
-if the filesystem was not unmounted cleanly,
+if the file system was not unmounted cleanly,
skipping the journal replay will lead to the
-filesystem containing inconsistencies that can
+file system 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.\&
+on the root file system, 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.
+main file system.
.TP
.B ordered
This is the default mode. All data is forced directly out to the main file
.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.
+file system 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
+internal file system integrity, however it can allow old data to appear
in files after a crash and journal recovery.
.RE
.TP
.BR attr (5)
manual page.
.TP
-.BR usrjquota=aquota.user | grpjquota=aquota.group | jqfmt=vfsv0
+.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
-enables journaled quotas. For journaled quotas the mount options
+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
+file system 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. Journaled quotas have the
-advantage that even after a crash no quota check is required.
+quota system which quota database files to use. When the
+.B quota
+file system 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
+The ext4 file system is an advanced level of the ext3 file system which
incorporates scalability and reliability enhancements for supporting large
-filesystem.
+file system.
The options
-.B journal_dev, norecovery, noload, data, commit, orlov, oldalloc, [no]user_xattr
-.B [no]acl, bsddf, minixdf, debug, errors, data_err, grpid, bsdgroups, nogrpid
-.B sysvgroups, resgid, resuid, sb, quota, noquota, nouid32, grpquota, usrquota
-.B usrjquota, grpjquota and jqfmt
-are backwardly compatible with ext3 or ext2.
+.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
-Enable 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.
+.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
"barrier" and "nobarrier" are added for consistency with other ext4 mount
options.
-The ext4 filesystem enables write barriers by default.
+The ext4 file system enables write barriers by default.
.TP
.BI inode_readahead_blks= n
This tuning parameter controls the maximum number of inode table blocks that
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
+Number of file system 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.
+RAID chunk size in file system blocks.
.TP
.B delalloc
Deferring block allocation until write-out time.
to page cache.
.TP
.BI max_batch_time= usec
-Maximum amount of time ext4 should wait for additional filesystem operations to
+Maximum amount of time ext4 should wait for additional file system 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
.B abort
Simulate the effects of calling ext4_abort() for
debugging purposes. This is normally used while
-remounting a filesystem which is already mounted.
+remounting a file system which is already mounted.
.TP
.BR auto_da_alloc | noauto_da_alloc
Many broken applications don't use fsync() when
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.
+then be deferred until the next time the file system 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.
+system performance while the file system's inode table is being initialized.
.TP
.BR discard / nodiscard
Controls whether ext4 should issue discard/TRIM commands to the underlying
testing has been done.
.TP
.BR block_validity / noblock_validity
-This options enables/disables the in-kernel facility for tracking
-filesystem metadata blocks within internal data structures. This allows multi-\c
+This option enables/disables the in-kernel facility for tracking
+file system 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
+overlap with file system 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
.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 file system.
+You need the quota utilities to actually enable and manage the quota system.
+This mount option requires the
+.B project
+file system feature.
.SH FILE ATTRIBUTES
-The ext2, ext3, and ext4 filesystems support setting the following file
+The ext2, ext3, and ext4 file systems support setting the following file
attributes on Linux systems using the
.BR chattr (1)
utility:
.sp
.BR u " - undeletable"
.sp
-In addition, the ext3 and ext4 filesystems support the following flag:
+In addition, the ext3 and ext4 file systems support the following flag:
.sp
.BR j " - data journaling"
.sp
-Finally, the ext4 filesystem also supports the following flag:
+Finally, the ext4 file system also supports the following flag:
.sp
.BR e " - extents format"
.sp
ext4, 3.18
.IP "\fBencrypt\fR" 2in
ext4, 4.1
-.IP "\fBproject\fR" 2in
+.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
+.IP "\fBstable_inodes\fR" 2i
+ext4, 5.5
.SH SEE ALSO
.BR mke2fs (8),
.BR mke2fs.conf (5),