mirror of https://github.com/vitalif/e2fsprogs
Clarify and clean up the ext4(5) man page
Signed-off-by: Pete Haddow <pete@leptonyx.com> Signed-off-by: Theodore Ts'o <tytso@mit.edu>debian
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@ -18,10 +18,10 @@ extensibility and backwards compatibility. In particular, file systems
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previously intended for use with the ext2 and ext3 file systems can be
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mounted using the ext4 file system driver, and indeed in many modern
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Linux distributions, the ext4 file system driver has been configured
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handle mount requests for ext2 and ext3 file systems.
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to handle mount requests for ext2 and ext3 file systems.
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.SH FILE SYSTEM FEATURES
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A file system formatted for ext2, ext3, or ext4 can be have some
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collection of the follow file system feature flags enabled. Some of
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A file system formatted for ext2, ext3, or ext4 can have some
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collection of the following file system feature flags enabled. Some of
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these features are not supported by all implementations of the ext2,
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ext3, and ext4 file system drivers, depending on Linux kernel version in
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use. On other operating systems, such as the GNU/HURD or FreeBSD, only
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@ -47,18 +47,20 @@ indicates whether a cluster is in use or not, where a cluster is by
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default composed of 16 blocks. This feature can decrease the time
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spent on doing block allocation and brings smaller fragmentation, especially
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for large files. The size can be specified using the
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.B \-C option.
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.B mke2fs \-C
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option.
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.IP
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.B Warning:
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The bigalloc feature is still under development, and may not be fully
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supported with your kernel or may have various bugs. Please see the web
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page http://ext4.wiki.kernel.org/index.php/Bigalloc for details.
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May clash with delayed allocation (see
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.BR nodelalloc mount option).
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.B nodelalloc
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mount option).
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.IP
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This feature requires that the
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.B extent
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features be enabled.
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feature be enabled.
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.TP
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.B dir_index
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.br
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@ -70,6 +72,11 @@ ext2 file systems.
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.br
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This ext4 feature allows more than 65000 subdirectories per directory.
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.TP
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.B ext_attr
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.br
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This feature enables the use of extended attributes. This feature is
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supported by ext2, ext3, and ext4.
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.TP
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.B extent
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.br
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This ext4 feature allows the mapping of logical block numbers for a
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@ -91,22 +98,17 @@ historical/backwards compatibility reasons.)
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.br
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This ext4 feature reserves a specific amount of space in each inode for
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extended metadata such as nanosecond timestamps and file creation time,
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even if the current kernel does not current need to reserve this much
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even if the current kernel does not currently need to reserve this much
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space. Without this feature, the kernel will reserve the amount of
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space for features currently it currently needs, and the rest may be
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space for features it currently needs, and the rest may be
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consumed by extended attributes.
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For this feature to be useful the inode size must be 256 bytes in size
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or larger.
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.TP
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.B ext_attr
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.br
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This feature enables the use of extended attributes. This feature is
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supported by ext2, ext3, and ext4.
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.TP
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.B filetype
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.br
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This feature enables the storage file type information in directory
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This feature enables the storage of file type information in directory
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entries. This feature is supported by ext2, ext3, and ext4.
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.TP
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.B flex_bg
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@ -127,13 +129,18 @@ option.
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Create a journal to ensure filesystem consistency even across unclean
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shutdowns. Setting the filesystem feature is equivalent to using the
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.B \-j
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option. This feature is supported by ext3 and ext4, and ignored by the
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option with
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.BR mke2fs " or " tune2fs.
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This feature is supported by ext3 and ext4, and ignored by the
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ext2 file system driver.
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.TP
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.B huge_file
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.br
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This ext4 feature allows files to be larger than 2 terabytes in size.
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.TP
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.B inline_data
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Allow data to be stored in the inode and extended attribute area.
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.TP
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.B journal_dev
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.br
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This feature is enabled on the superblock found on an external journal
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@ -149,9 +156,6 @@ option to
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or
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.BR tune2fs(8).
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.TP
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.B inline_data
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Allow data to be stored in the inode and extended attribute area
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.TP
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.B large_file
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.br
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This feature flag is set automatically by modern kernels when a file
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@ -174,17 +178,6 @@ kernels from mounting file systems that they could not understand.
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.\" .br
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.\" .B Future feature, available in e2fsprogs 1.43-WIP
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.TP
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.B sparse_super2
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.br
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This feature indicates that there will only at most two backup
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superblock and block group descriptors. The block groups used to store
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the backup superblock and blockgroup descriptors are stored in the
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superblock, but typically, one will be located at the beginning of block
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group #1, and one in the last block group in the file system. This is
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feature is essentially a more extreme version of sparse_super and is
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designed to allow the a much larger percentage of the disk to have
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contiguous blocks available for data files.
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.TP
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.B meta_bg
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.br
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This ext4 feature allows file systems to be resized on-line without explicitly
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@ -192,7 +185,7 @@ needing to reserve space for growth in the size of the block group
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descriptors. This scheme is also used to resize file systems which are
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larger than 2^32 blocks. It is not recommended that this feature be set
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when a file system is created, since this alternate method of storing
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the block group descriptor will slow down the time needed to mount the
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the block group descriptors will slow down the time needed to mount the
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file system, and newer kernels can automatically set this feature as
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necessary when doing an online resize and no more reserved space is
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available in the resize inode.
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@ -202,13 +195,6 @@ available in the resize inode.
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This ext4 feature provides multiple mount protection (MMP). MMP helps to
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protect the filesystem from being multiply mounted and is useful in
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shared storage environments.
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.TP
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.B quota
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.br
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Create quota inodes (inode #3 for userquota and inode
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#4 for group quota) and set them in the superblock.
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With this feature, the quotas will be enabled
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automatically when the filesystem is mounted.
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.IP
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Causes the quota files (i.e., user.quota and
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group.quota which existed
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@ -219,12 +205,19 @@ in the older quota design) to be hidden inodes.
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This ext4 feature provides project quota support. With this feature,
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the project ID of inode will be managed when the filesystem is mounted.
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.TP
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.B quota
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.br
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Create quota inodes (inode #3 for userquota and inode
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#4 for group quota) and set them in the superblock.
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With this feature, the quotas will be enabled
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automatically when the filesystem is mounted.
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.TP
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.B resize_inode
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.br
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This file system feature indicates that space has been reserved so
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the block group descriptor table can be extended by the file system is
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resized while the file system is mounted. The online resize operation
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is carried out by the kernel, triggered, by
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This file system feature indicates that space has been reserved so that
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the block group descriptor table can be extended while resizing a mounted
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file system. The online resize operation
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is carried out by the kernel, triggered by
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.BR resize2fs (8).
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By default
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.B mke2fs
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@ -241,10 +234,21 @@ feature be enabled.
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.B sparse_super
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.br
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This file system feature is set on all modern ext2, ext3, and ext4 file
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system. It indicates that backup copies of the superblock and block
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group descriptors be present only on a few block groups, and not all of
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systems. It indicates that backup copies of the superblock and block
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group descriptors are present only in a few block groups, not all of
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them.
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.TP
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.B sparse_super2
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.br
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This feature indicates that there will only be at most two backup
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superblocks and block group descriptors. The block groups used to store
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the backup superblock(s) and blockgroup descriptor(s) are stored in the
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superblock, but typically, one will be located at the beginning of block
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group #1, and one in the last block group in the file system. This
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feature is essentially a more extreme version of sparse_super and is
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designed to allow a much larger percentage of the disk to have
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contiguous blocks available for data files.
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.TP
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.B uninit_bg
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.br
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This ext4 file system feature indicates that the block group descriptors
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@ -252,7 +256,7 @@ will be protected using checksums, making it safe for
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.BR mke2fs (8)
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to create a file system without initializing all of the block groups.
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The kernel will keep a high watermark of unused inodes, and initialize
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inode tables and block lazily. This feature speeds up the time to check
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inode tables and blocks lazily. This feature speeds up the time to check
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the file system using
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.BR e2fsck (8),
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and it also speeds up the time required for
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