Documentation/admin-guide/ext4.rst

1 .. SPDX-License-Identifier: GPL-2.0
9 (64 bit) in keeping with increasing disk capacities and state-of-the-art
12 Mailing list:	linux-ext4@vger.kernel.org
23   - The latest version of e2fsprogs can be found at:
35   - Create a new filesystem using the ext4 filesystem type:
37         # mke2fs -t ext4 /dev/hda1
41 	# tune2fs -O extents /dev/hda1
46         # tune2fs -I 256 /dev/hda1
48   - Mounting:
50 	# mount -t ext4 /dev/hda1 /wherever
52   - When comparing performance with other filesystems, it's always
59     '-o barriers=[0|1]' mount option for both ext3 and ext4 filesystems
61     it is often worthwhile to try changing the data journaling mode; '-o
67     metadata-intensive workloads.
73 -------------------
77 * extent format more robust in face of on-disk corruption due to magics,
79 * improved file allocation (multi-block alloc)
94 * Case-insensitive file name lookups
95 * file-based encryption support (fscrypt)
96 * file-based verity support (fsverity)
101 case-insensitive file name lookups
104 The case-insensitive file name lookup feature is supported on a
105 per-directory basis, allowing the user to mix case-insensitive and
106 case-sensitive directories in the same filesystem.  It is enabled by
108 case-insensitive string match operation is only defined when we know how
110 case-insensitive directories, the filesystem must have the
111 casefold feature, which stores the filesystem-wide encoding
113 Unicode (12.1.0, by the time of this writing), encoded in the UTF-8
118 The case-awareness is name-preserving on the disk, meaning that the file
119 name provided by userspace is a byte-per-byte match to what is actually
123 used on large case-insensitive directories with DX feature.  On DX
136 operate on that file, but the case-insensitive lookups won't work.
146         thus write to the partition) even when mounted "read only". The mount
191         performance, but it's good for data-safety.  Setting it to 0 will have
203         proper on-disk ordering of journal commits, making volatile disk write
205         battery-backed in one way or another, disabling barriers may safely
212         that ext4's inode table readahead algorithm will pre-read into the
239   errors=remount-ro
240         Remount the filesystem read-only on an error.
275         documentation in the quota-tools package for more details
281         the above quota options. See documentation in the quota-tools package
319         parameter may improve the throughput of multi-threaded, synchronous
333         will detect the replace-via-rename and replace-via-truncate patterns
338         ext3, and avoids the "zero-length" problem that can happen when a
357         devices and sparse/thinly-provisioned LUNs, but it is off by default
361         Disables 32-bit UIDs and GIDs.  This is for interoperability  with
362         older kernels which only store and expect 16-bit values.
365         These options enable or disable the in-kernel facility for tracking
367         allows multi- block allocator and other routines to notice bugs or
379         used for extent-based files.  Because of the restrictions this options
391         Enable 64-bit inode version support. This option is off by default.
400         blk-crypto framework rather than filesystem-layer encryption. This
401         allows the use of inline encryption hardware. The on-disk format is
403         Documentation/block/inline-encryption.rst.
413   mode - metadata journaling.  A crash+recovery can cause incorrect data to
442 /proc/fs/ext4/dm-0).   The files in each per-device directory are shown
456 /sys/fs/ext4/dm-0).   The files in each per-device directory are shown
461 (see also Documentation/ABI/testing/sysfs-fs-ext4)
464         This file is read-only and shows the number of blocks that are dirty in
469         Tuning parameter which (if non-zero) controls the goal inode used by
476         blocks that ext4's inode table readahead algorithm will pre-read into
480         This file is read-only and shows the number of kilobytes of data that
517         This file is read-only and shows the number of kilobytes of data that
533 ext4-specific functionality. An incomplete list of these ioctls is shown in the
534 table below. This list includes truly ext4-specific ioctls (``EXT4_IOC_*``) as
535 well as ioctls that may have been ext4-specific originally but are now supported
594         application-expected ext3 behaviour. Note that this will also start
621 useful links:	https://fedoraproject.org/wiki/ext3-devel