.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 dir_nlink
.br
-This ext4 feature allows more than 65000 subdirectories per directory.
+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
-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
option to
.BR mke2fs (8)
or
-.BR tune2fs(8).
+.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
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 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 provides multiple mount protection (MMP). MMP helps to
protect the filesystem 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
#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
.IP
This feature requires that the
.B sparse_super
+or
+.B sparse_super2
feature be enabled.
.TP
.B sparse_super
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
(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
+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
-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 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
disabling barriers may safely improve performance.
.TP
.BI commit= nrsec
-Sync all data and metadata every
+Start a journal commit every
.I nrsec
-seconds. The default value is 5 seconds. Zero means default.
+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 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
+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. 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
+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
filesystem.
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
testing has been done.
.TP
.BR block_validity / noblock_validity
-This options enables/disables the in-kernel facility for tracking
+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
.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
ext4, 3.8
.IP "\fBsparse_super2\fR" 2in
ext4, 3.16
-.IP "\fBmetdata_csum\fR" 2in
+.IP "\fBmetadata_csum\fR" 2in
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
.SH SEE ALSO
.BR mke2fs (8),
.BR mke2fs.conf (5),
git://git.whamcloud.com / tools / e2fsprogs.git / blobdiff