^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 1) .. SPDX-License-Identifier: GPL-2.0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 2)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 3) ========================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 4) ext4 General Information
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 5) ========================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 6)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 7) Ext4 is an advanced level of the ext3 filesystem which incorporates
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 8) scalability and reliability enhancements for supporting large filesystems
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 9) (64 bit) in keeping with increasing disk capacities and state-of-the-art
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 10) feature requirements.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 11)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 12) Mailing list: linux-ext4@vger.kernel.org
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 13) Web site: http://ext4.wiki.kernel.org
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 14)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 15)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 16) Quick usage instructions
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 17) ========================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 18)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 19) Note: More extensive information for getting started with ext4 can be
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 20) found at the ext4 wiki site at the URL:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 21) http://ext4.wiki.kernel.org/index.php/Ext4_Howto
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 22)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 23) - The latest version of e2fsprogs can be found at:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 24)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 25) https://www.kernel.org/pub/linux/kernel/people/tytso/e2fsprogs/
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 26)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 27) or
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 28)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 29) http://sourceforge.net/project/showfiles.php?group_id=2406
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 30)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 31) or grab the latest git repository from:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 32)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 33) https://git.kernel.org/pub/scm/fs/ext2/e2fsprogs.git
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 34)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 35) - Create a new filesystem using the ext4 filesystem type:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 36)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 37) # mke2fs -t ext4 /dev/hda1
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 38)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 39) Or to configure an existing ext3 filesystem to support extents:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 40)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 41) # tune2fs -O extents /dev/hda1
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 42)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 43) If the filesystem was created with 128 byte inodes, it can be
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 44) converted to use 256 byte for greater efficiency via:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 45)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 46) # tune2fs -I 256 /dev/hda1
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 47)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 48) - Mounting:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 49)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 50) # mount -t ext4 /dev/hda1 /wherever
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 51)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 52) - When comparing performance with other filesystems, it's always
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 53) important to try multiple workloads; very often a subtle change in a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 54) workload parameter can completely change the ranking of which
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 55) filesystems do well compared to others. When comparing versus ext3,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 56) note that ext4 enables write barriers by default, while ext3 does
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 57) not enable write barriers by default. So it is useful to use
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 58) explicitly specify whether barriers are enabled or not when via the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 59) '-o barriers=[0|1]' mount option for both ext3 and ext4 filesystems
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 60) for a fair comparison. When tuning ext3 for best benchmark numbers,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 61) it is often worthwhile to try changing the data journaling mode; '-o
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 62) data=writeback' can be faster for some workloads. (Note however that
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 63) running mounted with data=writeback can potentially leave stale data
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 64) exposed in recently written files in case of an unclean shutdown,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 65) which could be a security exposure in some situations.) Configuring
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 66) the filesystem with a large journal can also be helpful for
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 67) metadata-intensive workloads.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 68)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 69) Features
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 70) ========
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 71)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 72) Currently Available
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 73) -------------------
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 74)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 75) * ability to use filesystems > 16TB (e2fsprogs support not available yet)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 76) * extent format reduces metadata overhead (RAM, IO for access, transactions)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 77) * extent format more robust in face of on-disk corruption due to magics,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 78) * internal redundancy in tree
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 79) * improved file allocation (multi-block alloc)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 80) * lift 32000 subdirectory limit imposed by i_links_count[1]
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 81) * nsec timestamps for mtime, atime, ctime, create time
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 82) * inode version field on disk (NFSv4, Lustre)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 83) * reduced e2fsck time via uninit_bg feature
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 84) * journal checksumming for robustness, performance
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 85) * persistent file preallocation (e.g for streaming media, databases)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 86) * ability to pack bitmaps and inode tables into larger virtual groups via the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 87) flex_bg feature
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 88) * large file support
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 89) * inode allocation using large virtual block groups via flex_bg
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 90) * delayed allocation
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 91) * large block (up to pagesize) support
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 92) * efficient new ordered mode in JBD2 and ext4 (avoid using buffer head to force
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 93) the ordering)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 94) * Case-insensitive file name lookups
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 95) * file-based encryption support (fscrypt)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 96) * file-based verity support (fsverity)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 97)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 98) [1] Filesystems with a block size of 1k may see a limit imposed by the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 99) directory hash tree having a maximum depth of two.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 100)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 101) case-insensitive file name lookups
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 102) ======================================================
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 103)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 104) The case-insensitive file name lookup feature is supported on a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 105) per-directory basis, allowing the user to mix case-insensitive and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 106) case-sensitive directories in the same filesystem. It is enabled by
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 107) flipping the +F inode attribute of an empty directory. The
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 108) case-insensitive string match operation is only defined when we know how
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 109) text in encoded in a byte sequence. For that reason, in order to enable
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 110) case-insensitive directories, the filesystem must have the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 111) casefold feature, which stores the filesystem-wide encoding
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 112) model used. By default, the charset adopted is the latest version of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 113) Unicode (12.1.0, by the time of this writing), encoded in the UTF-8
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 114) form. The comparison algorithm is implemented by normalizing the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 115) strings to the Canonical decomposition form, as defined by Unicode,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 116) followed by a byte per byte comparison.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 117)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 118) The case-awareness is name-preserving on the disk, meaning that the file
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 119) name provided by userspace is a byte-per-byte match to what is actually
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 120) written in the disk. The Unicode normalization format used by the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 121) kernel is thus an internal representation, and not exposed to the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 122) userspace nor to the disk, with the important exception of disk hashes,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 123) used on large case-insensitive directories with DX feature. On DX
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 124) directories, the hash must be calculated using the casefolded version of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 125) the filename, meaning that the normalization format used actually has an
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 126) impact on where the directory entry is stored.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 127)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 128) When we change from viewing filenames as opaque byte sequences to seeing
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 129) them as encoded strings we need to address what happens when a program
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 130) tries to create a file with an invalid name. The Unicode subsystem
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 131) within the kernel leaves the decision of what to do in this case to the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 132) filesystem, which select its preferred behavior by enabling/disabling
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 133) the strict mode. When Ext4 encounters one of those strings and the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 134) filesystem did not require strict mode, it falls back to considering the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 135) entire string as an opaque byte sequence, which still allows the user to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 136) operate on that file, but the case-insensitive lookups won't work.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 137)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 138) Options
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 139) =======
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 140)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 141) When mounting an ext4 filesystem, the following option are accepted:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 142) (*) == default
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 143)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 144) ro
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 145) Mount filesystem read only. Note that ext4 will replay the journal (and
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 146) thus write to the partition) even when mounted "read only". The mount
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 147) options "ro,noload" can be used to prevent writes to the filesystem.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 148)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 149) journal_checksum
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 150) Enable checksumming of the journal transactions. This will allow the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 151) recovery code in e2fsck and the kernel to detect corruption in the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 152) kernel. It is a compatible change and will be ignored by older
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 153) kernels.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 154)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 155) journal_async_commit
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 156) Commit block can be written to disk without waiting for descriptor
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 157) blocks. If enabled older kernels cannot mount the device. This will
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 158) enable 'journal_checksum' internally.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 159)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 160) journal_path=path, journal_dev=devnum
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 161) When the external journal device's major/minor numbers have changed,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 162) these options allow the user to specify the new journal location. The
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 163) journal device is identified through either its new major/minor numbers
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 164) encoded in devnum, or via a path to the device.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 165)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 166) norecovery, noload
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 167) Don't load the journal on mounting. Note that if the filesystem was
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 168) not unmounted cleanly, skipping the journal replay will lead to the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 169) filesystem containing inconsistencies that can lead to any number of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 170) problems.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 171)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 172) data=journal
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 173) All data are committed into the journal prior to being written into the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 174) main file system. Enabling this mode will disable delayed allocation
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 175) and O_DIRECT support.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 176)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 177) data=ordered (*)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 178) All data are forced directly out to the main file system prior to its
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 179) metadata being committed to the journal.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 180)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 181) data=writeback
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 182) Data ordering is not preserved, data may be written into the main file
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 183) system after its metadata has been committed to the journal.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 184)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 185) commit=nrsec (*)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 186) This setting limits the maximum age of the running transaction to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 187) 'nrsec' seconds. The default value is 5 seconds. This means that if
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 188) you lose your power, you will lose as much as the latest 5 seconds of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 189) metadata changes (your filesystem will not be damaged though, thanks
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 190) to the journaling). This default value (or any low value) will hurt
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 191) performance, but it's good for data-safety. Setting it to 0 will have
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 192) the same effect as leaving it at the default (5 seconds). Setting it
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 193) to very large values will improve performance. Note that due to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 194) delayed allocation even older data can be lost on power failure since
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 195) writeback of those data begins only after time set in
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 196) /proc/sys/vm/dirty_expire_centisecs.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 197)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 198) barrier=<0|1(*)>, barrier(*), nobarrier
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 199) This enables/disables the use of write barriers in the jbd code.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 200) barrier=0 disables, barrier=1 enables. This also requires an IO stack
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 201) which can support barriers, and if jbd gets an error on a barrier
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 202) write, it will disable again with a warning. Write barriers enforce
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 203) proper on-disk ordering of journal commits, making volatile disk write
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 204) caches safe to use, at some performance penalty. If your disks are
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 205) battery-backed in one way or another, disabling barriers may safely
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 206) improve performance. The mount options "barrier" and "nobarrier" can
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 207) also be used to enable or disable barriers, for consistency with other
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 208) ext4 mount options.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 209)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 210) inode_readahead_blks=n
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 211) This tuning parameter controls the maximum number of inode table blocks
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 212) that ext4's inode table readahead algorithm will pre-read into the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 213) buffer cache. The default value is 32 blocks.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 214)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 215) nouser_xattr
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 216) Disables Extended User Attributes. See the attr(5) manual page for
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 217) more information about extended attributes.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 218)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 219) noacl
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 220) This option disables POSIX Access Control List support. If ACL support
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 221) is enabled in the kernel configuration (CONFIG_EXT4_FS_POSIX_ACL), ACL
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 222) is enabled by default on mount. See the acl(5) manual page for more
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 223) information about acl.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 224)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 225) bsddf (*)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 226) Make 'df' act like BSD.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 227)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 228) minixdf
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 229) Make 'df' act like Minix.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 230)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 231) debug
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 232) Extra debugging information is sent to syslog.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 233)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 234) abort
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 235) Simulate the effects of calling ext4_abort() for debugging purposes.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 236) This is normally used while remounting a filesystem which is already
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 237) mounted.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 238)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 239) errors=remount-ro
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 240) Remount the filesystem read-only on an error.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 241)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 242) errors=continue
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 243) Keep going on a filesystem error.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 244)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 245) errors=panic
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 246) Panic and halt the machine if an error occurs. (These mount options
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 247) override the errors behavior specified in the superblock, which can be
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 248) configured using tune2fs)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 249)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 250) data_err=ignore(*)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 251) Just print an error message if an error occurs in a file data buffer in
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 252) ordered mode.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 253) data_err=abort
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 254) Abort the journal if an error occurs in a file data buffer in ordered
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 255) mode.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 256)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 257) grpid | bsdgroups
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 258) New objects have the group ID of their parent.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 259)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 260) nogrpid (*) | sysvgroups
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 261) New objects have the group ID of their creator.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 262)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 263) resgid=n
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 264) The group ID which may use the reserved blocks.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 265)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 266) resuid=n
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 267) The user ID which may use the reserved blocks.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 268)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 269) sb=
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 270) Use alternate superblock at this location.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 271)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 272) quota, noquota, grpquota, usrquota
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 273) These options are ignored by the filesystem. They are used only by
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 274) quota tools to recognize volumes where quota should be turned on. See
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 275) documentation in the quota-tools package for more details
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 276) (http://sourceforge.net/projects/linuxquota).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 277)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 278) jqfmt=<quota type>, usrjquota=<file>, grpjquota=<file>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 279) These options tell filesystem details about quota so that quota
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 280) information can be properly updated during journal replay. They replace
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 281) the above quota options. See documentation in the quota-tools package
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 282) for more details (http://sourceforge.net/projects/linuxquota).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 283)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 284) stripe=n
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 285) Number of filesystem blocks that mballoc will try to use for allocation
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 286) size and alignment. For RAID5/6 systems this should be the number of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 287) data disks * RAID chunk size in file system blocks.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 288)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 289) delalloc (*)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 290) Defer block allocation until just before ext4 writes out the block(s)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 291) in question. This allows ext4 to better allocation decisions more
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 292) efficiently.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 293)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 294) nodelalloc
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 295) Disable delayed allocation. Blocks are allocated when the data is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 296) copied from userspace to the page cache, either via the write(2) system
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 297) call or when an mmap'ed page which was previously unallocated is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 298) written for the first time.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 299)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 300) max_batch_time=usec
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 301) Maximum amount of time ext4 should wait for additional filesystem
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 302) operations to be batch together with a synchronous write operation.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 303) Since a synchronous write operation is going to force a commit and then
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 304) a wait for the I/O complete, it doesn't cost much, and can be a huge
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 305) throughput win, we wait for a small amount of time to see if any other
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 306) transactions can piggyback on the synchronous write. The algorithm
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 307) used is designed to automatically tune for the speed of the disk, by
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 308) measuring the amount of time (on average) that it takes to finish
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 309) committing a transaction. Call this time the "commit time". If the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 310) time that the transaction has been running is less than the commit
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 311) time, ext4 will try sleeping for the commit time to see if other
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 312) operations will join the transaction. The commit time is capped by
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 313) the max_batch_time, which defaults to 15000us (15ms). This
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 314) optimization can be turned off entirely by setting max_batch_time to 0.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 315)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 316) min_batch_time=usec
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 317) This parameter sets the commit time (as described above) to be at least
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 318) min_batch_time. It defaults to zero microseconds. Increasing this
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 319) parameter may improve the throughput of multi-threaded, synchronous
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 320) workloads on very fast disks, at the cost of increasing latency.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 321)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 322) journal_ioprio=prio
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 323) The I/O priority (from 0 to 7, where 0 is the highest priority) which
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 324) should be used for I/O operations submitted by kjournald2 during a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 325) commit operation. This defaults to 3, which is a slightly higher
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 326) priority than the default I/O priority.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 327)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 328) auto_da_alloc(*), noauto_da_alloc
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 329) Many broken applications don't use fsync() when replacing existing
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 330) files via patterns such as fd = open("foo.new")/write(fd,..)/close(fd)/
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 331) rename("foo.new", "foo"), or worse yet, fd = open("foo",
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 332) O_TRUNC)/write(fd,..)/close(fd). If auto_da_alloc is enabled, ext4
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 333) will detect the replace-via-rename and replace-via-truncate patterns
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 334) and force that any delayed allocation blocks are allocated such that at
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 335) the next journal commit, in the default data=ordered mode, the data
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 336) blocks of the new file are forced to disk before the rename() operation
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 337) is committed. This provides roughly the same level of guarantees as
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 338) ext3, and avoids the "zero-length" problem that can happen when a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 339) system crashes before the delayed allocation blocks are forced to disk.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 340)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 341) noinit_itable
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 342) Do not initialize any uninitialized inode table blocks in the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 343) background. This feature may be used by installation CD's so that the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 344) install process can complete as quickly as possible; the inode table
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 345) initialization process would then be deferred until the next time the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 346) file system is unmounted.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 347)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 348) init_itable=n
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 349) The lazy itable init code will wait n times the number of milliseconds
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 350) it took to zero out the previous block group's inode table. This
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 351) minimizes the impact on the system performance while file system's
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 352) inode table is being initialized.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 353)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 354) discard, nodiscard(*)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 355) Controls whether ext4 should issue discard/TRIM commands to the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 356) underlying block device when blocks are freed. This is useful for SSD
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 357) devices and sparse/thinly-provisioned LUNs, but it is off by default
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 358) until sufficient testing has been done.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 359)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 360) nouid32
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 361) Disables 32-bit UIDs and GIDs. This is for interoperability with
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 362) older kernels which only store and expect 16-bit values.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 363)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 364) block_validity(*), noblock_validity
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 365) These options enable or disable the in-kernel facility for tracking
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 366) filesystem metadata blocks within internal data structures. This
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 367) allows multi- block allocator and other routines to notice bugs or
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 368) corrupted allocation bitmaps which cause blocks to be allocated which
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 369) overlap with filesystem metadata blocks.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 370)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 371) dioread_lock, dioread_nolock
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 372) Controls whether or not ext4 should use the DIO read locking. If the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 373) dioread_nolock option is specified ext4 will allocate uninitialized
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 374) extent before buffer write and convert the extent to initialized after
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 375) IO completes. This approach allows ext4 code to avoid using inode
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 376) mutex, which improves scalability on high speed storages. However this
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 377) does not work with data journaling and dioread_nolock option will be
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 378) ignored with kernel warning. Note that dioread_nolock code path is only
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 379) used for extent-based files. Because of the restrictions this options
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 380) comprises it is off by default (e.g. dioread_lock).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 381)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 382) max_dir_size_kb=n
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 383) This limits the size of directories so that any attempt to expand them
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 384) beyond the specified limit in kilobytes will cause an ENOSPC error.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 385) This is useful in memory constrained environments, where a very large
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 386) directory can cause severe performance problems or even provoke the Out
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 387) Of Memory killer. (For example, if there is only 512mb memory
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 388) available, a 176mb directory may seriously cramp the system's style.)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 389)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 390) i_version
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 391) Enable 64-bit inode version support. This option is off by default.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 392)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 393) dax
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 394) Use direct access (no page cache). See
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 395) Documentation/filesystems/dax.txt. Note that this option is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 396) incompatible with data=journal.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 397)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 398) inlinecrypt
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 399) When possible, encrypt/decrypt the contents of encrypted files using the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 400) blk-crypto framework rather than filesystem-layer encryption. This
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 401) allows the use of inline encryption hardware. The on-disk format is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 402) unaffected. For more details, see
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 403) Documentation/block/inline-encryption.rst.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 404)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 405) Data Mode
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 406) =========
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 407) There are 3 different data modes:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 408)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 409) * writeback mode
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 410)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 411) In data=writeback mode, ext4 does not journal data at all. This mode provides
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 412) a similar level of journaling as that of XFS, JFS, and ReiserFS in its default
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 413) mode - metadata journaling. A crash+recovery can cause incorrect data to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 414) appear in files which were written shortly before the crash. This mode will
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 415) typically provide the best ext4 performance.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 416)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 417) * ordered mode
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 418)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 419) In data=ordered mode, ext4 only officially journals metadata, but it logically
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 420) groups metadata information related to data changes with the data blocks into
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 421) a single unit called a transaction. When it's time to write the new metadata
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 422) out to disk, the associated data blocks are written first. In general, this
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 423) mode performs slightly slower than writeback but significantly faster than
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 424) journal mode.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 425)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 426) * journal mode
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 427)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 428) data=journal mode provides full data and metadata journaling. All new data is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 429) written to the journal first, and then to its final location. In the event of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 430) a crash, the journal can be replayed, bringing both data and metadata into a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 431) consistent state. This mode is the slowest except when data needs to be read
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 432) from and written to disk at the same time where it outperforms all others
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 433) modes. Enabling this mode will disable delayed allocation and O_DIRECT
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 434) support.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 435)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 436) /proc entries
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 437) =============
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 438)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 439) Information about mounted ext4 file systems can be found in
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 440) /proc/fs/ext4. Each mounted filesystem will have a directory in
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 441) /proc/fs/ext4 based on its device name (i.e., /proc/fs/ext4/hdc or
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 442) /proc/fs/ext4/dm-0). The files in each per-device directory are shown
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 443) in table below.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 444)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 445) Files in /proc/fs/ext4/<devname>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 446)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 447) mb_groups
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 448) details of multiblock allocator buddy cache of free blocks
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 449)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 450) /sys entries
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 451) ============
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 452)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 453) Information about mounted ext4 file systems can be found in
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 454) /sys/fs/ext4. Each mounted filesystem will have a directory in
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 455) /sys/fs/ext4 based on its device name (i.e., /sys/fs/ext4/hdc or
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 456) /sys/fs/ext4/dm-0). The files in each per-device directory are shown
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 457) in table below.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 458)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 459) Files in /sys/fs/ext4/<devname>:
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 460)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 461) (see also Documentation/ABI/testing/sysfs-fs-ext4)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 462)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 463) delayed_allocation_blocks
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 464) This file is read-only and shows the number of blocks that are dirty in
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 465) the page cache, but which do not have their location in the filesystem
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 466) allocated yet.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 467)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 468) inode_goal
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 469) Tuning parameter which (if non-zero) controls the goal inode used by
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 470) the inode allocator in preference to all other allocation heuristics.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 471) This is intended for debugging use only, and should be 0 on production
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 472) systems.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 473)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 474) inode_readahead_blks
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 475) Tuning parameter which controls the maximum number of inode table
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 476) blocks that ext4's inode table readahead algorithm will pre-read into
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 477) the buffer cache.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 478)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 479) lifetime_write_kbytes
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 480) This file is read-only and shows the number of kilobytes of data that
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 481) have been written to this filesystem since it was created.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 482)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 483) max_writeback_mb_bump
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 484) The maximum number of megabytes the writeback code will try to write
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 485) out before move on to another inode.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 486)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 487) mb_group_prealloc
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 488) The multiblock allocator will round up allocation requests to a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 489) multiple of this tuning parameter if the stripe size is not set in the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 490) ext4 superblock
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 491)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 492) mb_max_inode_prealloc
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 493) The maximum length of per-inode ext4_prealloc_space list.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 494)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 495) mb_max_to_scan
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 496) The maximum number of extents the multiblock allocator will search to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 497) find the best extent.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 498)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 499) mb_min_to_scan
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 500) The minimum number of extents the multiblock allocator will search to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 501) find the best extent.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 502)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 503) mb_order2_req
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 504) Tuning parameter which controls the minimum size for requests (as a
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 505) power of 2) where the buddy cache is used.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 506)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 507) mb_stats
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 508) Controls whether the multiblock allocator should collect statistics,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 509) which are shown during the unmount. 1 means to collect statistics, 0
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 510) means not to collect statistics.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 511)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 512) mb_stream_req
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 513) Files which have fewer blocks than this tunable parameter will have
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 514) their blocks allocated out of a block group specific preallocation
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 515) pool, so that small files are packed closely together. Each large file
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 516) will have its blocks allocated out of its own unique preallocation
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 517) pool.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 518)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 519) session_write_kbytes
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 520) This file is read-only and shows the number of kilobytes of data that
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 521) have been written to this filesystem since it was mounted.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 522)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 523) reserved_clusters
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 524) This is RW file and contains number of reserved clusters in the file
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 525) system which will be used in the specific situations to avoid costly
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 526) zeroout, unexpected ENOSPC, or possible data loss. The default is 2% or
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 527) 4096 clusters, whichever is smaller and this can be changed however it
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 528) can never exceed number of clusters in the file system. If there is not
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 529) enough space for the reserved space when mounting the file mount will
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 530) _not_ fail.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 531)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 532) Ioctls
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 533) ======
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 534)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 535) Ext4 implements various ioctls which can be used by applications to access
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 536) ext4-specific functionality. An incomplete list of these ioctls is shown in the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 537) table below. This list includes truly ext4-specific ioctls (``EXT4_IOC_*``) as
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 538) well as ioctls that may have been ext4-specific originally but are now supported
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 539) by some other filesystem(s) too (``FS_IOC_*``).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 540)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 541) Table of Ext4 ioctls
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 542)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 543) FS_IOC_GETFLAGS
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 544) Get additional attributes associated with inode. The ioctl argument is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 545) an integer bitfield, with bit values described in ext4.h.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 546)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 547) FS_IOC_SETFLAGS
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 548) Set additional attributes associated with inode. The ioctl argument is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 549) an integer bitfield, with bit values described in ext4.h.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 550)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 551) EXT4_IOC_GETVERSION, EXT4_IOC_GETVERSION_OLD
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 552) Get the inode i_generation number stored for each inode. The
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 553) i_generation number is normally changed only when new inode is created
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 554) and it is particularly useful for network filesystems. The '_OLD'
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 555) version of this ioctl is an alias for FS_IOC_GETVERSION.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 556)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 557) EXT4_IOC_SETVERSION, EXT4_IOC_SETVERSION_OLD
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 558) Set the inode i_generation number stored for each inode. The '_OLD'
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 559) version of this ioctl is an alias for FS_IOC_SETVERSION.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 560)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 561) EXT4_IOC_GROUP_EXTEND
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 562) This ioctl has the same purpose as the resize mount option. It allows
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 563) to resize filesystem to the end of the last existing block group,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 564) further resize has to be done with resize2fs, either online, or
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 565) offline. The argument points to the unsigned logn number representing
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 566) the filesystem new block count.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 567)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 568) EXT4_IOC_MOVE_EXT
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 569) Move the block extents from orig_fd (the one this ioctl is pointing to)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 570) to the donor_fd (the one specified in move_extent structure passed as
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 571) an argument to this ioctl). Then, exchange inode metadata between
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 572) orig_fd and donor_fd. This is especially useful for online
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 573) defragmentation, because the allocator has the opportunity to allocate
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 574) moved blocks better, ideally into one contiguous extent.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 575)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 576) EXT4_IOC_GROUP_ADD
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 577) Add a new group descriptor to an existing or new group descriptor
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 578) block. The new group descriptor is described by ext4_new_group_input
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 579) structure, which is passed as an argument to this ioctl. This is
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 580) especially useful in conjunction with EXT4_IOC_GROUP_EXTEND, which
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 581) allows online resize of the filesystem to the end of the last existing
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 582) block group. Those two ioctls combined is used in userspace online
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 583) resize tool (e.g. resize2fs).
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 584)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 585) EXT4_IOC_MIGRATE
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 586) This ioctl operates on the filesystem itself. It converts (migrates)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 587) ext3 indirect block mapped inode to ext4 extent mapped inode by walking
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 588) through indirect block mapping of the original inode and converting
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 589) contiguous block ranges into ext4 extents of the temporary inode. Then,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 590) inodes are swapped. This ioctl might help, when migrating from ext3 to
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 591) ext4 filesystem, however suggestion is to create fresh ext4 filesystem
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 592) and copy data from the backup. Note, that filesystem has to support
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 593) extents for this ioctl to work.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 594)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 595) EXT4_IOC_ALLOC_DA_BLKS
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 596) Force all of the delay allocated blocks to be allocated to preserve
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 597) application-expected ext3 behaviour. Note that this will also start
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 598) triggering a write of the data blocks, but this behaviour may change in
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 599) the future as it is not necessary and has been done this way only for
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 600) sake of simplicity.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 601)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 602) EXT4_IOC_RESIZE_FS
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 603) Resize the filesystem to a new size. The number of blocks of resized
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 604) filesystem is passed in via 64 bit integer argument. The kernel
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 605) allocates bitmaps and inode table, the userspace tool thus just passes
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 606) the new number of blocks.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 607)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 608) EXT4_IOC_SWAP_BOOT
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 609) Swap i_blocks and associated attributes (like i_blocks, i_size,
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 610) i_flags, ...) from the specified inode with inode EXT4_BOOT_LOADER_INO
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 611) (#5). This is typically used to store a boot loader in a secure part of
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 612) the filesystem, where it can't be changed by a normal user by accident.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 613) The data blocks of the previous boot loader will be associated with the
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 614) given inode.
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 615)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 616) References
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 617) ==========
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 618)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 619) kernel source: <file:fs/ext4/>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 620) <file:fs/jbd2/>
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 621)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 622) programs: http://e2fsprogs.sourceforge.net/
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 623)
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 624) useful links: https://fedoraproject.org/wiki/ext3-devel
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 625) http://www.bullopensource.org/ext4/
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 626) http://ext4.wiki.kernel.org/index.php/Main_Page
^8f3ce5b39 (kx 2023-10-28 12:00:06 +0300 627) https://fedoraproject.org/wiki/Features/Ext4
Orange Pi5 kernel
Deprecated Linux kernel 5.10.110 for OrangePi 5/5B/5+ boards
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