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EXT4(5)                       File Formats ManualEXT4(5)NAME       ext2 - the second extended file system       ext3 - the third extended file system       ext4 - the fourth extended file systemDESCRIPTION       The second, third, and fourth extended file systems, or ext2, ext3, and       ext4 as they are commonly known, are Linux file systems that have  his-       torically  been  the  default file system for many Linux distributions.       They are general purpose file systems that have been designed  for  ex-       tensibility  and  backwards compatibility.  In particular, file systems       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 to       handle mount requests for ext2 and ext3 file systems.FILE SYSTEM FEATURES       A  file  system formatted for ext2, ext3, or ext4 can have some collec-       tion 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.       64bit              Enables  the  file  system  to be larger than 2^32 blocks.  This              feature is set automatically, as needed, but it can be useful to              specify this feature explicitly if the file system might need to              be resized larger than 2^32 blocks, even if it was smaller  than              that  threshold  when it was originally created.  Note that some              older kernels and older versions of e2fsprogs will  not  support              file systems with this ext4 feature enabled.       bigalloc              This  ext4  feature  enables clustered block allocation, so that              the unit of allocation is a power of two number of blocks.  That              is,  each  bit  in  the what had traditionally been known as the              block allocation bitmap now indicates whether a  cluster  is  in              use or not, where a cluster is by default composed of 16 blocks.              This feature can decrease the time spent on doing block  alloca-              tion  and  brings  smaller  fragmentation,  especially for large              files.  The size can be specified using the mke2fs -C option.              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/in-              dex.php/Bigalloc for details.  May clash with delayed allocation              (see nodelalloc mount option).              This feature requires that the extent feature be enabled.       casefold              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  ap-              plications  to lookup for a file in the file system using an en-              coding equivalent version of the file name.       dir_index              Use hashed b-trees to speed up name lookups  in  large  directo-              ries.   This feature is supported by ext3 and ext4 file systems,              and is ignored by ext2 file systems.       dir_nlink              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  di-              rectory  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.       ea_inode              Normally, a file's extended attributes and  associated  metadata              must fit within the inode or the inode's associated extended at-              tribute 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  ex-              tended attributes per file.       encrypt              Enables  support for file-system level encryption of data blocks              and file names.  The  inode  metadata  (timestamps,  file  size,              user/group ownership, etc.) is not encrypted.              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 de-              vice layer using dm-crypt may provide much better security.       ext_attr              This feature enables the use of extended attributes.  This  fea-              ture is supported by ext2, ext3, and ext4.       extent              This  ext4  feature  allows the mapping of logical block numbers              for a particular inode to physical blocks on the storage  device              to  be  stored  using  an extent tree, which is a more efficient              data structure than the traditional indirect block  scheme  used              by  the  ext2 and ext3 file systems.  The use of the extent tree              decreases metadata block overhead, improves file system  perfor-              mance,  and  decreases  the  needed to rune2fsck(8) on the file              system.  (Note: both extent and extents are  accepted  as  valid              names  for  this  feature for historical/backwards compatibility              reasons.)       extra_isize              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  cur-              rently  need  to reserve this much space.  Without this feature,              the kernel will reserve the amount of space for features it cur-              rently  needs,  and  the  rest  may  be consumed by extended at-              tributes.              For this feature to be useful the inode size must be  256  bytes              in size or larger.       filetype              This feature enables the storage of file type information in di-              rectory entries.  This feature is supported by ext2,  ext3,  and              ext4.       flex_bg              This  ext4  feature allows the per-block group metadata (alloca-              tion bitmaps and inode tables) to  be  placed  anywhere  on  the              storage  media.   In  addition,  mke2fs will place the per-block              group metadata together starting at the  first  block  group  of              each  "flex_bg  group".    The  size of the flex_bg group can be              specified using the -G option.       has_journal              Create a journal to ensure filesystem  consistency  even  across              unclean shutdowns.  Setting the filesystem feature is equivalent              to using the -j option with mke2fs or tune2fs.  This feature  is              supported  by ext3 and ext4, and ignored by the ext2 file system              driver.       huge_file              This ext4 feature allows files to be larger than 2 terabytes  in              size.       inline_data              Allow  data  to  be  stored  in the inode and extended attribute              area.       journal_dev              This feature is enabled on the superblock found on  an  external              journal device.  The block size for the external journal must be              the same as the file system which uses it.              The external journal device can be used  by  a  file  system  by              specifying  the  -J device=<external-device> option tomke2fs(8)              ortune2fs(8).       large_dir              This feature increases the limit on the number of files per  di-              rectory  by  raising  the  maximum  size of directories and, for              hashed b-tree directories (see dir_index), the maximum height of              the hashed b-tree used to store the directory entries.       large_file              This  feature flag is set automatically by modern kernels when a              file larger than 2 gigabytes is created.  Very old kernels could              not  handle  large  files, so this feature flag was used to pro-              hibit those kernels from mounting file systems that  they  could              not understand.       metadata_csum              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 de-              scriptors with the uninit_bg feature.  These  two  features  are              incompatible  and  metadata_csum will be used preferentially in-              stead of uninit_bg.       metadata_csum_seed              This feature allows the filesystem to store the metadata  check-              sum  seed  in  the superblock, which allows the administrator to              change the UUID of a filesystem using the metadata_csum  feature              while it is mounted.       meta_bg              This  ext4  feature  allows  file  systems to be resized on-line              without explicitly needing to reserve space for  growth  in  the              size  of  the block group 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              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.       mmp              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.       project              This ext4 feature provides project quota support. With this fea-              ture,  the project ID of inode will be managed when the filesys-              tem is mounted.       quota              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.              Causes  the  quota files (i.e., user.quota and group.quota which              existed in the older quota design) to be hidden inodes.       resize_inode              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 byresize2fs(8).  By de-              fault mke2fs will attempt to reserve enough space  so  that  the              filesystem may grow to 1024 times its initial size.  This can be              changed using the resize extended option.              This feature requires that  the  sparse_super  or  sparse_super2              feature be enabled.       sparse_super              This  file  system  feature is set on all modern ext2, ext3, and              ext4 file systems.  It indicates that backup copies of  the  su-              perblock  and  block group descriptors are present only in a few              block groups, not all of them.       sparse_super2              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 de-              scriptor(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 essen-              tially 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.       uninit_bg              This ext4 file system feature indicates that the block group de-              scriptors  will be protected using checksums, making it safe formke2fs(8) to create a file system without  initializing  all  of              the  block groups.  The kernel will keep a high watermark of un-              used inodes, and initialize  inode  tables  and  blocks  lazily.              This  feature  speeds up the time to check the file system usinge2fsck(8), and it also speeds up the time required formke2fs(8)              to create the file system.       verity              Enables  support  for  verity protected files.  Verity files are              readonly, and their data is  transparently  verified  against  a              Merkle  tree  hidden past the end of the file.  Using the Merkle              tree's root hash, a verity file  can  be  efficiently  authenti-              cated, independent of the file's size.              This  feature  is most useful for authenticating important read-              only files on read-write file systems.  If the file  system  it-              self  is read-only, then using dm-verity to authenticate the en-              tire block device may provide much better security.MOUNT OPTIONS       This section describes mount options which are specific to ext2,  ext3,       and  ext4.   Other  generic  mount  options  may  be  used as well; seemount(8) for details.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 withtune2fs(8).       acl|noacl              Support POSIX Access Control Lists (or  not).   See  theacl(5)              manual page.       bsddf|minixdf              Set  the behavior for the statfs system call. The minixdf behav-              ior is to return in the  f_blocks  field  the  total  number  of              blocks of the filesystem, while the bsddf behavior (which is the              default) is to subtract the overhead blocks  used  by  the  ext2              filesystem and not available for file storage. Thus              % mount /k -o minixdf; df /k; umount /k              Filesystem  1024-blocks   Used  Available  Capacity  Mounted on              /dev/sda6     2630655    86954   2412169      3%     /k              % mount /k -o bsddf; df /k; umount /k              Filesystem  1024-blocks  Used  Available  Capacity  Mounted on              /dev/sda6     2543714      13   2412169      0%     /k              (Note  that this example shows that one can add command line op-              tions to the options given in /etc/fstab.)       check=none or nocheck              No checking is done at mount time. This is the default. This  is              fast.   It  is wise to invokee2fsck(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 ker-              nel driver is used for ext2 and ext3 filesystems.       debug  Print debugging info upon each (re)mount.       errors={continue|remount-ro|panic}              Define  the  behavior when an error is encountered.  (Either ig-              nore errors and just mark the filesystem erroneous and continue,              or  remount the filesystem read-only, or panic and halt the sys-              tem.)  The default is set in the filesystem superblock, and  can              be changed usingtune2fs(8).       grpid|bsdgroups and nogrpid|sysvgroups              These  options  define  what group id a newly created file gets.              When 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.       grpquota|noquota|quota|usrquota              The usrquota (same as quota) mount  option  enables  user  quota              support  on  the  filesystem. grpquota enables group quotas sup-              port. You need the quota utilities to actually enable and manage              the quota system.       nouid32              Disables  32-bit  UIDs  and  GIDs.  This is for interoperability              with older kernels which only store and expect 16-bit values.       oldalloc or orlov              Use old allocator or Orlov allocator for new  inodes.  Orlov  is              default.       resgid=n and resuid=n              The  ext2 filesystem reserves a certain percentage of the avail-              able space (by default 5%, seemke2fs(8) andtune2fs(8)).  These              options  determine  who  can use the reserved blocks.  (Roughly:              whoever has the specified  uid,  or  belongs  to  the  specified              group.)       sb=n   Instead  of  using the normal superblock, use an alternative su-              perblock specified by 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 num-              ber of blocks per group, and features such as sparse_super.              Additional  backup  superblocks  can  be determined by using the              mke2fs program using the -n option to print out  where  the  su-              perblocks  exist,  supposing  mke2fs  is supplied with arguments              that are consistent with the filesystem's  layout  (e.g.  block-              size, blocks per group, sparse_super, etc.).              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".       user_xattr|nouser_xattr              Support "user." extended attributes (or not).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:       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.       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.       data={journal|ordered|writeback}              Specifies the journaling mode for file data.  Metadata is always              journaled.  To use modes other than ordered on the root filesys-              tem, pass the mode to the kernel as boot parameter,  e.g.  root-              flags=data=journal.              journal                     All  data  is  committed  into the journal prior to being                     written into the main filesystem.              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.              writeback                     Data ordering is not preserved - 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 in-                     tegrity, however it can allow old data to appear in files                     after a crash and journal recovery.       data_err=ignore              Just  print  an  error message if an error occurs in a file data              buffer in ordered mode.       data_err=abort              Abort the journal if an error occurs in a file  data  buffer  in              ordered mode.       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  im-              prove performance.       commit=nrsec              Start  a  journal commit every nrsec seconds.  The default value              is 5 seconds.  Zero means default.       user_xattr              Enable Extended User Attributes. See theattr(5) manual page.       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 quota  filesystem  feature  is              enabled, journaled quotas are used automatically, and this mount              option is ignored.       usrjquota=aquota.user|grpjquota=aquota.group              For journaled quotas (jqfmt=vfsv0 or jqfmt=vfsv1), the mount op-              tions  usrjquota=aquota.user  and grpjquota=aquota.group are re-              quired to tell the quota system which quota  database  files  to              use.  When  the  quota  filesystem feature is enabled, journaled              quotas are used automatically, and this mount option is ignored.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 journal_dev, journal_path, norecovery, noload,  data,  com-       mit,  orlov,  oldalloc, [no]user_xattr, [no]acl, bsddf, minixdf, debug,       errors, data_err, grpid, bsdgroups, nogrpid,  sysvgroups,  resgid,  re-       suid,  sb,  quota, noquota, nouid32, grpquota, usrquota, usrjquota, gr-       pjquota, and jqfmt are backwardly compatible with ext3 or ext2.       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  compati-              ble change and will be ignored by older kernels.       journal_async_commit              Commit block can be written to disk without waiting for descrip-              tor blocks. If enabled older kernels cannot  mount  the  device.              This will enable 'journal_checksum' internally.       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.       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 de-              fault value is 32 blocks.       stripe=n              Number of filesystem blocks that mballoc will try to use for al-              location  size and alignment. For RAID5/6 systems this should be              the number of data disks * RAID chunk size in filesystem blocks.       delalloc              Deferring block allocation until write-out time.       nodelalloc              Disable delayed allocation. Blocks are allocated  when  data  is              copied from user to page cache.       max_batch_time=usec              Maximum  amount of time ext4 should wait for additional filesys-              tem operations to be batch together with a synchronous write op-              eration. 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 auto-              matically 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 oper-              ations  will  join the transaction. The commit time is capped by              the max_batch_time, which defaults  to  15000 <micro>s  (15 ms).              This   optimization  can  be  turned  off  entirely  by  setting              max_batch_time to 0.       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. In-              creasing this parameter may improve  the  throughput  of  multi-              threaded,  synchronous workloads on very fast disks, at the cost              of increasing latency.       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.       abort  Simulate  the effects of calling ext4_abort() for debugging pur-              poses.  This is normally  used  while  remounting  a  filesystem              which is already mounted.       auto_da_alloc|noauto_da_alloc              Many broken applications don't use fsync() when replacing exist-              ing 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  de-              layed  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.       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.       init_itable=n              The  lazy  itable init code will wait n times the number of mil-              liseconds 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.       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.       block_validity/noblock_validity              This option enables/disables the in-kernel facility for tracking              filesystem metadata blocks within internal data structures. This              allows  multi-block  allocator and other routines to quickly lo-              cate  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.       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 unini-              tialized 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).       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 environ-              ments, 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.)       i_version              Enable  64-bit  inode version support. This option is off by de-              fault.       nombcache              This option disables use of mbcache for extended attribute dedu-              plication.  On  systems  where extended attributes are rarely or              never shared between files, use  of  mbcache  for  deduplication              adds unnecessary computational overhead.       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 project              filesystem feature.FILE ATTRIBUTES       The ext2, ext3, and ext4 filesystems support setting the following file       attributes on Linux systems using thechattr(1) utility:       a - append only       A - no atime updates       d - no dump       D - synchronous directory updates       i - immutable       S - synchronous updates       u - undeletable       In addition, the ext3 and ext4 filesystems support the following flag:       j - data journaling       Finally, the ext4 filesystem also supports the following flag:       e - extents format       For  descriptions  of  these  attribute  flags,  please  refer  to  thechattr(1) man page.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 sup-       ported.  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  dis-       tributions" can be extremely misleading.       filetype            ext2, 2.2.0       sparse_super        ext2, 2.2.0       large_file          ext2, 2.2.0       has_journal         ext3, 2.4.15       ext_attr            ext2/ext3, 2.6.0       dir_index           ext3, 2.6.0       resize_inode        ext3, 2.6.10 (online resizing)       64bit               ext4, 2.6.28       dir_nlink           ext4, 2.6.28       extent              ext4, 2.6.28       extra_isize         ext4, 2.6.28       flex_bg             ext4, 2.6.28       huge_file           ext4, 2.6.28       meta_bg             ext4, 2.6.28       uninit_bg           ext4, 2.6.28       mmp                 ext4, 3.0       bigalloc            ext4, 3.2       quota               ext4, 3.6       inline_data         ext4, 3.8       sparse_super2       ext4, 3.16       metadata_csum       ext4, 3.18       encrypt             ext4, 4.1       metadata_csum_seed  ext4, 4.4       project             ext4, 4.5       ea_inode            ext4, 4.13       large_dir           ext4, 4.13       casefold            ext4, 5.2       verity              ext4, 5.4SEE ALSOmke2fs(8),mke2fs.conf(5),e2fsck(8),dumpe2fs(8),tune2fs(8),  de-bugfs(8),mount(8),chattr(1)E2fsprogs version 1.45.5         January 2020EXT4(5)