.SH NAME
ext2 \- the second extended file system
.br
-ext2 \- the third extended file system
+ext3 \- the third extended file system
.br
ext4 \- the fourth extended file system
.SH DESCRIPTION
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
-handle mount requests for ext2 and ext3 file systems.
+to handle mount requests for ext2 and ext3 file systems.
.SH FILE SYSTEM FEATURES
-A file system formated for ext2, ext3, or ext4 can be have some
-collection of the follow file system feature flags enabled. Some of
+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.
-.RS 1.2i
.TP
.B 64bit
.br
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 \-C option.
+.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
-.BR nodelalloc mount option).
+.B nodelalloc
+mount option).
.IP
This feature requires that the
.B extent
-features be enabled.
+feature be enabled.
.TP
.B dir_index
.br
.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
+.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
.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 current need to reserve this much
+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 currently it currently needs, and the rest may be
+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 ext_attr
-.br
-This feature enables the use of extended attributes. This feature is
-supported by ext2, ext3, and ext4.
-.TP
.B filetype
.br
-This feature enables the storage file type information in directory
+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
.B \-G
option.
.TP
+.B fname_encoding
+.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 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. This feature is supported by ext3 and ext4, and ignored by the
+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
option to
.BR mke2fs (8)
or
-.BR tune2fs(8).
+.BR tune2fs(8) .
.TP
-.B inline_data
-Allow data to be stored in the inode and extended attribute area
+.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 sparse_super2
+.B metadata_csum
.br
-This feature indicates that there will only at most two backup
-superblock and block group descriptors. The block groups used to store
-the backup superblock and blockgroup descriptors 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 is
-feature is essentially a more extreme version of sparse_super and is
-designed to allow the a much larger percentage of the disk to have
-contiguous blocks available for data files.
+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
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 descriptor will slow down the time needed to mount the
+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.
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.
-@QUOTA_MAN_COMMENT@.TP
-@QUOTA_MAN_COMMENT@.B quota
-@QUOTA_MAN_COMMENT@.br
-@QUOTA_MAN_COMMENT@Create quota inodes (inode #3 for userquota and inode
-@QUOTA_MAN_COMMENT@#4 for group quota) and set them in the superblock.
-@QUOTA_MAN_COMMENT@With this feature, the quotas will be enabled
-@QUOTA_MAN_COMMENT@automatically when the filesystem is mounted.
-@QUOTA_MAN_COMMENT@.IP
-@QUOTA_MAN_COMMENT@Causes the quota files (i.e., user.quota and
-@QUOTA_MAN_COMMENT@group.quota which existed
-@QUOTA_MAN_COMMENT@in the older quota design) to be hidden inodes.
-@QUOTA_MAN_COMMENT@.IP
-@QUOTA_MAN_COMMENT@.B Warning:
-@QUOTA_MAN_COMMENT@The quota feature is still under development,
-@QUOTA_MAN_COMMENT@and may not be fully supported with your kernel
-@QUOTA_MAN_COMMENT@or may have various bugs. Please
-@QUOTA_MAN_COMMENT@see https://ext4.wiki.kernel.org/index.php/Quota
-@QUOTA_MAN_COMMENT@for more details.
+.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
-the block group descriptor table can be extended by the file system is
-resized while the file system is mounted. The online resize operation
-is carried out by the kernel, triggered, by
+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
.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
-system. It indicates that backup copies of the superblock and block
-group descriptors be present only on a few block groups, and not all of
+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
.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 block lazily. This feature speeds up the time to check
+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.
+.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
.SH SEE ALSO
.BR mke2fs (8),
.BR mke2fs.conf (5),
.BR e2fsck (8),
.BR dumpe2fs (8),
.BR tune2fs (8),
-.BR debugfs (8)
+.BR debugfs (8),
+.BR mount (8),
+.BR chattr (1)
projects / thirdparty / e2fsprogs.git / blobdiff