{
    "mode": "man",
    "parameter": "TUNE2FS",
    "section": "8",
    "url": "https://www.chedong.com/phpMan.php/man/TUNE2FS/8/json",
    "generated": "2026-06-13T19:43:04Z",
    "synopsis": "tune2fs  [  -l ] [ -c max-mount-counts ] [ -e errors-behavior ] [ -f ] [ -i interval-between-\nchecks ] [ -I newinodesize ] [ -j ] [ -J journal-options ] [ -m  reserved-blocks-percentage\n]  [  -o [^]mount-options[,...]  ] [ -r reserved-blocks-count ] [ -u user ] [ -g group ] [ -C\nmount-count ] [ -E extended-options ] [ -L volume-label ] [ -M last-mounted-directory ] [  -O\n[^]feature[,...]   ] [ -Q quota-options ] [ -T time-last-checked ] [ -U UUID ] [ -z undofile\n] device",
    "sections": {
        "NAME": {
            "content": "tune2fs - adjust tunable file system parameters on ext2/ext3/ext4 file systems\n",
            "subsections": []
        },
        "SYNOPSIS": {
            "content": "tune2fs  [  -l ] [ -c max-mount-counts ] [ -e errors-behavior ] [ -f ] [ -i interval-between-\nchecks ] [ -I newinodesize ] [ -j ] [ -J journal-options ] [ -m  reserved-blocks-percentage\n]  [  -o [^]mount-options[,...]  ] [ -r reserved-blocks-count ] [ -u user ] [ -g group ] [ -C\nmount-count ] [ -E extended-options ] [ -L volume-label ] [ -M last-mounted-directory ] [  -O\n[^]feature[,...]   ] [ -Q quota-options ] [ -T time-last-checked ] [ -U UUID ] [ -z undofile\n] device\n",
            "subsections": []
        },
        "DESCRIPTION": {
            "content": "tune2fs allows the system administrator to adjust various tunable file system  parameters  on\nLinux ext2, ext3, or ext4 file systems.  The current values of these options can be displayed\nby using the -l option to tune2fs(8) program, or by using the dumpe2fs(8) program.\n\nThe device specifier can either be a filename (i.e., /dev/sda1), or a LABEL  or  UUID  speci‐\nfier:  \"LABEL=volume-label\"  or  \"UUID=uuid\".   (i.e., LABEL=home or UUID=e40486c6-84d5-4f2f-\nb99c-032281799c9d).\n",
            "subsections": []
        },
        "OPTIONS": {
            "content": "",
            "subsections": [
                {
                    "name": "-c",
                    "content": "Adjust the number of mounts after which the file system will be checked by  e2fsck(8).\nIf max-mount-counts is the string \"random\", tune2fs will use a random value between 20\nand 40.  If max-mount-counts is 0 or -1, the  number  of  times  the  file  system  is\nmounted will be disregarded by e2fsck(8) and the kernel.\n\nStaggering  the mount-counts at which file systems are forcibly checked will avoid all\nfile systems being checked at one time when using journaled file systems.\n\nMount-count-dependent checking is disabled by default to avoid unanticipated long  re‐\nboots  while e2fsck does its work.  If you are concerned about file system corruptions\ncaused by potential hardware problems of kernel bugs, a better  solution  than  mount-\ncount-dependent  checking is to use the e2scrub(8) program.  This does require placing\nthe file system on an LVM volume, however.\n",
                    "flag": "-c"
                },
                {
                    "name": "-C",
                    "content": "Set the number of times the file system has been mounted.  If set to a  greater  value\nthan  the  max-mount-counts  parameter  set by the -c option, e2fsck(8) will check the\nfile system at the next reboot.\n",
                    "flag": "-C"
                },
                {
                    "name": "-e",
                    "content": "Change the behavior of the kernel code when errors are detected.  In all cases, a file\nsystem  error  will cause e2fsck(8) to check the file system on the next boot.  error-\nbehavior can be one of the following:\n\ncontinue    Continue normal execution.\n\nremount-ro  Remount file system read-only.\n\npanic       Cause a kernel panic.\n",
                    "flag": "-e"
                },
                {
                    "name": "-E",
                    "content": "Set extended options for the file system.  Extended options are comma  separated,  and\nmay  take an argument using the equals ('=') sign.  The following extended options are\nsupported:\n\nclearmmp\nReset the MMP block (if any) back to the clean state.  Use only  if  abso‐\nlutely certain the device is not currently mounted or being fscked, or ma‐\njor file system corruption can result.  Needs '-f'.\n\nmmpupdateinterval=interval\nAdjust the initial MMP update interval to interval seconds.  Specifying an\ninterval  of  0 means to use the default interval.  The specified interval\nmust be less than 300 seconds.  Requires that the mmp feature be enabled.\n\nstride=stride-size\nConfigure the file system for a RAID array with  stride-size  file  system\nblocks. This is the number of blocks read or written to disk before moving\nto next disk. This mostly affects placement of file system  metadata  like\nbitmaps  at  mke2fs(2)  time to avoid placing them on a single disk, which\ncan hurt the performance.  It may also be used by block allocator.\n\nstripewidth=stripe-width\nConfigure the file system for a RAID array with stripe-width  file  system\nblocks  per  stripe.  This is typically be stride-size * N, where N is the\nnumber of data disks in the RAID (e.g. RAID 5 N+1, RAID 6 N+2).  This  al‐\nlows  the  block allocator to prevent read-modify-write of the parity in a\nRAID stripe if possible when the data is written.\n\nhashalg=hash-alg\nSet the default hash algorithm used for file systems  with  hashed  b-tree\ndirectories.  Valid algorithms accepted are: legacy, halfmd4, and tea.\n\nencoding=encoding-name\nEnable  the  casefold  feature in the super block and set encoding-name as\nthe encoding to be used.  If encoding-name is not specified, utf8 is used.\nThe encoding cannot be altered if casefold was previously enabled.\n\nencodingflags=encoding-flags\nDefine  parameters for file name character encoding operations.  If a flag\nis not changed using this parameter, its default value is used.  encoding-\nflags should be a comma-separated lists of flags to be enabled.  The flags\ncannot be altered if casefold was previously enabled.\n\nThe only flag that can be set right now is strict which means that invalid\nstrings  should be rejected by the file system.  In the default configura‐\ntion, the strict flag is disabled.\n\nmountopts=mountoptionstring\nSet a set of default mount options which will be used when the file system\nis  mounted.   Unlike the bitmask-based default mount options which can be\nspecified with the -o option, mountoptionstring is an  arbitrary  string\nwith a maximum length of 63 bytes, which is stored in the superblock.\n\nThe ext4 file system driver will first apply the bitmask-based default op‐\ntions, and then parse the mountoptionstring, before  parsing  the  mount\noptions passed from the mount(8) program.\n\nThis superblock setting is only honored in 2.6.35+ kernels; and not at all\nby the ext2 and ext3 file system drivers.\n\nforcefsck\nSet a flag in the file system superblock indicating that errors have  been\nfound.  This will force fsck to run at the next mount.\n\ntestfs\nSet a flag in the file system superblock indicating that it may be mounted\nusing experimental kernel code, such as the ext4dev file system.\n\n^testfs\nClear the testfs flag, indicating the file system should only be  mounted\nusing production-level file system code.\n",
                    "flag": "-E"
                },
                {
                    "name": "-f",
                    "content": "useful when removing the hasjournal file system feature from a file system which  has\nan  external  journal  (or is corrupted such that it appears to have an external jour‐\nnal), but that external journal is not available.   If the file system appears to  re‐\nquire journal replay, the -f flag must be specified twice to proceed.\n\nWARNING:  Removing  an  external  journal from a file system which was not cleanly un‐\nmounted without first replaying the external journal can result in  severe  data  loss\nand file system corruption.\n",
                    "flag": "-f"
                },
                {
                    "name": "-g",
                    "content": "Set  the group which can use the reserved file system blocks.  The group parameter can\nbe a numerical gid or a group name.  If a group name is given, it is  converted  to  a\nnumerical gid before it is stored in the superblock.\n",
                    "flag": "-g"
                },
                {
                    "name": "-i",
                    "content": "Adjust the maximal time between two file system checks.  No suffix or d will interpret\nthe number interval-between-checks as days, m as months, and w as weeks.  A  value  of\nzero will disable the time-dependent checking.\n\nThere  are  pros and cons to disabling these periodic checks; see the discussion under\nthe -c (mount-count-dependent check) option for details.\n",
                    "flag": "-i"
                },
                {
                    "name": "-I",
                    "content": "ble,  so  it  requires  that  the  file  system is checked for consistency first using\ne2fsck(8).  This operation can also take a while and the file system can be  corrupted\nand  data lost if it is interrupted while in the middle of converting the file system.\nBacking up the file system before changing inode size is recommended.\n\nFile systems with an inode size of 128 bytes do not support timestamps beyond  January\n19,  2038.   Inodes  which  are  256 bytes or larger will support extended timestamps,\nproject id's, and the ability to store some extended attributes in the inode table for\nimproved performance.\n",
                    "flag": "-I"
                },
                {
                    "name": "-j -J",
                    "content": "fault journal parameters will be used to create an appropriately sized journal  (given\nthe size of the file system) stored within the file system.  Note that you must be us‐\ning a kernel which has ext3 support in order to actually make use of the journal.\n\nIf this option is used to create a journal on a  mounted  file  system,  an  immutable\nfile,  .journal,  will be created in the top-level directory of the file system, as it\nis the only safe way to create the journal inode while the  file  system  is  mounted.\nWhile the ext3 journal is visible, it is not safe to delete it, or modify it while the\nfile system is mounted; for this reason the file is marked immutable.  While  checking\nunmounted file systems, e2fsck(8) will automatically move .journal files to the invis‐\nible, reserved journal inode.  For all file systems except for the root  file  system,\nthis  should  happen  automatically and naturally during the next reboot cycle.  Since\nthe root file system is mounted read-only, e2fsck(8) must be run from a rescue  floppy\nin order to effect this transition.\n\nOn  some  distributions,  such  as  Debian,  if an initial ramdisk is used, the initrd\nscripts will automatically convert an ext2 root file system to ext3 if the  /etc/fstab\nfile specifies the ext3 file system for the root file system in order to avoid requir‐\ning the use of a rescue floppy to add an ext3 journal to the root file system.\n",
                    "flag": "-J"
                },
                {
                    "name": "-J",
                    "content": "Override the default ext3 journal parameters. Journal options are comma separated, and\nmay  take an argument using the equals ('=')  sign.  The following journal options are\nsupported:\n\nsize=journal-size\nCreate a journal stored in the file system of size journal-size megabytes.\nThe  size  of  the journal must be at least 1024 file system blocks (i.e.,\n1MB if using 1k blocks, 4MB if using 4k blocks, etc.)  and may be no  more\nthan  10,240,000  file  system blocks.  There must be enough free space in\nthe file system to create a journal of that size.\n\nfastcommitsize=fast-commit-size\nCreate an additional fast commit journal  area  of  size  fast-commit-size\nkilobytes.  This option is only valid if fastcommit feature is enabled on\nthe file system. If this option is not specified and if  fastcommit  fea‐\nture  is  turned  on,  fast commit area size defaults to journal-size / 64\nmegabytes. The total size of the journal with fastcommit feature  set  is\njournal-size  +  (  fast-commit-size  * 1024) megabytes. The total journal\nsize may be no more than 10,240,000 file system blocks or half  the  total\nfile system size (whichever is smaller).\n\nlocation=journal-location\nSpecify  the  location  of the journal.  The argument journal-location can\neither be specified as a block number, or if the number has a units suffix\n(e.g.,  'M',  'G',  etc.) interpret it as the offset from the beginning of\nthe file system.\n\ndevice=external-journal\nAttach the file system to the journal block device  located  on  external-\njournal.   The  external  journal must have been already created using the\ncommand\n\nmke2fs -O journaldev external-journal\n\nNote that external-journal must be formatted with the same block  size  as\nfile  systems which will be using it.  In addition, while there is support\nfor attaching multiple file systems to  a  single  external  journal,  the\nLinux  kernel and e2fsck(8) do not currently support shared external jour‐\nnals yet.\n\nInstead of specifying a device name directly, external-journal can also be\nspecified  by either LABEL=label or UUID=UUID to locate the external jour‐\nnal by either the volume label or UUID stored in the  ext2  superblock  at\nthe  start  of the journal.  Use dumpe2fs(8) to display a journal device's\nvolume label and UUID.  See also the -L option of tune2fs(8).\n\nOnly one of the size or device options can be given for a file system.\n",
                    "flag": "-J"
                },
                {
                    "name": "-l",
                    "content": "parameters that can be set via this program.\n",
                    "flag": "-l"
                },
                {
                    "name": "-L",
                    "content": "Set  the  volume  label of the file system.  Ext2 file system labels can be at most 16\ncharacters long; if volume-label is longer than 16 characters, tune2fs  will  truncate\nit  and  print  a  warning.   The  volume  label can be used by mount(8), fsck(8), and\n/etc/fstab(5) (and possibly others) by  specifying  LABEL=volume-label  instead  of  a\nblock special device name like /dev/hda5.\n",
                    "flag": "-L"
                },
                {
                    "name": "-m",
                    "content": "Set  the  percentage of the file system which may only be allocated by privileged pro‐\ncesses.   Reserving some number of file system blocks for use by privileged  processes\nis  done to avoid file system fragmentation, and to allow system daemons, such as sys‐‐\nlogd(8), to continue to function correctly after  non-privileged  processes  are  pre‐\nvented  from writing to the file system.  Normally, the default percentage of reserved\nblocks is 5%.\n",
                    "flag": "-m"
                },
                {
                    "name": "-M",
                    "content": "Set the last-mounted directory for the file system.\n",
                    "flag": "-M"
                },
                {
                    "name": "-o",
                    "content": "Set or clear the indicated default mount options in the file  system.   Default  mount\noptions can be overridden by mount options specified either in /etc/fstab(5) or on the\ncommand line arguments to mount(8).  Older kernels may not support  this  feature;  in\nparticular,  kernels  which  predate  2.4.20  will almost certainly ignore the default\nmount options field in the superblock.\n\nMore than one mount option can be cleared or set by separating features  with  commas.\nMount  options  prefixed with a caret character ('^') will be cleared in the file sys‐\ntem's superblock; mount options without a prefix character or  prefixed  with  a  plus\ncharacter ('+') will be added to the file system.\n\nThe following mount options can be set or cleared using tune2fs:\n\ndebug  Enable debugging code for this file system.\n\nbsdgroups\nEmulate  BSD behavior when creating new files: they will take the group-id\nof the directory in which they were created.  The standard System V behav‐\nior  is  the  default,  where newly created files take on the fsgid of the\ncurrent process, unless the directory has the setgid  bit  set,  in  which\ncase  it takes the gid from the parent directory, and also gets the setgid\nbit set if it is a directory itself.\n\nuserxattr\nEnable user-specified extended attributes.\n\nacl    Enable Posix Access Control Lists.\n\nuid16  Disables 32-bit UIDs and GIDs.  This is for  interoperability  with  older\nkernels which only store and expect 16-bit values.\n\njournaldata\nWhen  the  file  system  is mounted with journaling enabled, all data (not\njust metadata) is committed into the journal prior to being  written  into\nthe main file system.\n\njournaldataordered\nWhen  the  file  system  is  mounted  with journaling enabled, all data is\nforced directly out to the main file system prior to  its  metadata  being\ncommitted to the journal.\n\njournaldatawriteback\nWhen the file system is mounted with journaling enabled, data may be writ‐\nten into the main file system after its metadata has been committed to the\njournal.   This may increase throughput, however, it may allow old data to\nappear in files after a crash and journal recovery.\n\nnobarrier\nThe file system will be mounted with barrier  operations  in  the  journal\ndisabled.   (This option is currently only supported by the ext4 file sys‐\ntem driver in 2.6.35+ kernels.)\n\nblockvalidity\nThe file system will be mounted with the  blockvalidity  option  enabled,\nwhich  causes  extra  checks to be performed after reading or writing from\nthe file system.  This prevents corrupted  metadata  blocks  from  causing\nfile  system damage by overwriting parts of the inode table or block group\ndescriptors.  This comes at the cost of increased memory and CPU overhead,\nso  it  is enabled only for debugging purposes.  (This option is currently\nonly supported by the ext4 file system driver in 2.6.35+ kernels.)\n\ndiscard\nThe file system will be mounted with the discard mount option.  This  will\ncause the file system driver to attempt to use the trim/discard feature of\nsome storage devices (such as SSD's and thin-provisioned drives  available\nin  some  enterprise  storage  arrays)  to  inform the storage device that\nblocks belonging to deleted files can be reused for other purposes.  (This\noption  is  currently  only  supported  by  the ext4 file system driver in\n2.6.35+ kernels.)\n\nnodelalloc\nThe file system will be mounted with the nodelalloc  mount  option.   This\nwill  disable  the  delayed allocation feature.  (This option is currently\nonly supported by the ext4 file system driver in 2.6.35+ kernels.)\n",
                    "flag": "-o"
                },
                {
                    "name": "-O",
                    "content": "Set or clear the indicated file system features (options) in the  file  system.   More\nthan one file system feature can be cleared or set by separating features with commas.\nFile System features prefixed with a caret character ('^') will be cleared in the file\nsystem's  superblock; file system features without a prefix character or prefixed with\na plus character ('+') will be added to the file system.  For a  detailed  description\nof the file system features, please see the man page ext4(5).\n\nThe following file system features can be set or cleared using tune2fs:\n\n64bit  Enable the file system to be larger than 2^32 blocks.\n\ncasefold\nEnable  support for file system level casefolding.  Tune2fs currently only\nsupports setting this file system feature.\n\ndirindex\nUse hashed b-trees to speed up lookups for large directories.\n\ndirnlink\nAllow more than 65000 subdirectories per directory.\n\neainode\nAllow the value of each extended attribute to be placed in the data blocks\nof  a  separate  inode  if necessary, increasing the limit on the size and\nnumber of extended attributes per file.  Tune2fs currently  only  supports\nsetting this file system feature.\n\nencrypt\nEnable  support  for file system level encryption.  Tune2fs currently only\nsupports setting this file system feature.\n\nextent Enable the use of extent trees to store the location of data blocks in in‐\nodes.  Tune2fs currently only supports setting this file system feature.\n\nextraisize\nEnable the extended inode fields used by ext4.\n\nfiletype\nStore file type information in directory entries.\n\nflexbg\nAllow  bitmaps and inode tables for a block group to be placed anywhere on\nthe storage media.  Tune2fs will not reorganize the location of the  inode\ntables  and  allocation  bitmaps,  as  mke2fs(8) will do when it creates a\nfreshly formatted file system with flexbg enabled.\n\nhasjournal\nUse a journal to ensure file system consistency even across unclean  shut‐\ndowns.   Setting the file system feature is equivalent to using the -j op‐\ntion.\n\n\nfastcommit\nEnable fast commit journaling feature to improve fsync latency.\n\nlargedir\nIncrease the limit on the number of files  per  directory.   Tune2fs  cur‐\nrently only supports setting this file system feature.\n\nhugefile\nSupport files larger than 2 terabytes in size.\n\nlargefile\nFile System can contain files that are greater than 2GB.\n\nmetadatacsum\nStore a checksum to protect the contents in each metadata block.\n\nmetadatacsumseed\nAllow  the  file  system  to  store  the metadata checksum seed in the su‐\nperblock, enabling the administrator to change the UUID of a  file  system\nusing the metadatacsum feature while it is mounted.\n\nmmp    Enable or disable multiple mount protection (MMP) feature.\n\nproject\nEnable project ID tracking.  This is used for project quota tracking.\n\nquota  Enable internal file system quota inodes.\n\nread-only\nForce the kernel to mount the file system read-only.\n\nresizeinode\nReserve  space so the block group descriptor table may grow in the future.\nTune2fs only supports clearing this file system feature.\n\nsparsesuper\nLimit the number of backup superblocks to save space on  large  file  sys‐\ntems.  Tune2fs currently only supports setting this file system feature.\n\nstableinodes\nPrevent  the  file system from being shrunk or having its UUID changed, in\norder to allow the use of specialized encryption settings that make use of\nthe  inode numbers and UUID.  Tune2fs currently only supports setting this\nfile system feature.\n\nuninitbg\nAllow the kernel to initialize bitmaps and inode  tables  lazily,  and  to\nkeep  a  high  watermark for the unused inodes in a file system, to reduce\ne2fsck(8) time.  The first e2fsck run after  enabling  this  feature  will\ntake  the  full time, but subsequent e2fsck runs will take only a fraction\nof the original time, depending on how full the file system is.\n\nverity Enable support for verity protected files.  Tune2fs  currently  only  sup‐\nports setting this file system feature.\n\nAfter setting or clearing sparsesuper, uninitbg, filetype, or resizeinode file sys‐\ntem features, the file system may require being checked using e2fsck(8) to return  the\nfile  system  to a consistent state.  Tune2fs will print a message requesting that the\nsystem administrator run e2fsck(8) if necessary.  After setting the dirindex feature,\ne2fsck -D can be run to convert existing directories to the hashed B-tree format.  En‐\nabling certain file system features may prevent the file system from being mounted  by\nkernels which do not support those features.  In particular, the uninitbg and flexbg\nfeatures are only supported by the ext4 file system.\n",
                    "flag": "-O"
                },
                {
                    "name": "-r",
                    "content": "Set the number of reserved file system blocks.\n",
                    "flag": "-r"
                },
                {
                    "name": "-Q",
                    "content": "Sets 'quota' feature on the superblock and works on the  quota  files  for  the  given\nquota type. Quota options could be one or more of the following:\n\n[^]usrquota\nSets/clears user quota inode in the superblock.\n\n[^]grpquota\nSets/clears group quota inode in the superblock.\n\n[^]prjquota\nSets/clears project quota inode in the superblock.\n",
                    "flag": "-Q"
                },
                {
                    "name": "-T",
                    "content": "Set  the  time the file system was last checked using e2fsck.  The time is interpreted\nusing the current (local) timezone.  This can be useful in scripts which use a Logical\nVolume Manager to make a consistent snapshot of a file system, and then check the file\nsystem during off hours to make sure it hasn't been corrupted due  to  hardware  prob‐\nlems, etc.  If the file system was clean, then this option can be used to set the last\nchecked time on the original file system.  The format of time-last-checked is the  in‐\nternational  date format, with an optional time specifier, i.e.  YYYYMMDD[HH[MM[SS]]].\nThe keyword now is also accepted, in which case the last checked time will be  set  to\nthe current time.\n",
                    "flag": "-T"
                },
                {
                    "name": "-u",
                    "content": "Set the user who can use the reserved file system blocks.  user can be a numerical uid\nor a user name.  If a user name is given, it is converted to a numerical uid before it\nis stored in the superblock.\n",
                    "flag": "-u"
                },
                {
                    "name": "-U",
                    "content": "Set  the  universally unique identifier (UUID) of the file system to UUID.  The format\nof  the  UUID  is  a  series  of  hex  digits  separated  by   hyphens,   like   this:\n\"c1b9d5a2-f162-11cf-9ece-0020afc76f16\".   The  UUID  parameter  may also be one of the\nfollowing:\n\nclear  clear the file system UUID\n\nrandom generate a new randomly-generated UUID\n\ntime   generate a new time-based UUID\n\nThe UUID may be used by mount(8), fsck(8), and /etc/fstab(5) (and possibly others)  by\nspecifying UUID=uuid instead of a block special device name like /dev/hda1.\n\nSee uuidgen(8) for more information.  If the system does not have a good random number\ngenerator such as /dev/random or /dev/urandom, tune2fs will automatically use a  time-\nbased UUID instead of a randomly-generated UUID.\n",
                    "flag": "-U"
                },
                {
                    "name": "-z",
                    "content": "Before overwriting a file system block, write the old contents of the block to an undo\nfile.  This undo file can be used with e2undo(8) to restore the old  contents  of  the\nfile system should something go wrong.  If the empty string is passed as the undofile\nargument, the undo file will be written to a file named tune2fs-device.e2undo  in  the\ndirectory specified via the E2FSPROGSUNDODIR environment variable.\n\nWARNING: The undo file cannot be used to recover from a power or system crash.\n",
                    "flag": "-z"
                }
            ]
        },
        "BUGS": {
            "content": "We haven't found any bugs yet.  That doesn't mean there aren't any...\n",
            "subsections": []
        },
        "AUTHOR": {
            "content": "tune2fs  was written by Remy Card <Remy.Card@linux.org>.  It is currently being maintained by\nTheodore Ts'o <tytso@alum.mit.edu>.  tune2fs uses the ext2fs library written by Theodore Ts'o\n<tytso@mit.edu>.   This  manual  page  was written by Christian Kuhtz <chk@data-hh.Hanse.DE>.\nTime-dependent checking was added by Uwe Ohse <uwe@tirka.gun.de>.\n",
            "subsections": []
        },
        "AVAILABILITY": {
            "content": "tune2fs is part of the e2fsprogs  package  and  is  available  from  http://e2fsprogs.source‐\nforge.net.\n",
            "subsections": []
        },
        "SEE ALSO": {
            "content": "debugfs(8), dumpe2fs(8), e2fsck(8), mke2fs(8), ext4(5)\n\n\n\nE2fsprogs version 1.46.5                    December 2021                                 TUNE2FS(8)",
            "subsections": []
        }
    },
    "summary": "tune2fs - adjust tunable file system parameters on ext2/ext3/ext4 file systems",
    "flags": [
        {
            "flag": "-c",
            "long": null,
            "arg": null,
            "description": "Adjust the number of mounts after which the file system will be checked by e2fsck(8). If max-mount-counts is the string \"random\", tune2fs will use a random value between 20 and 40. If max-mount-counts is 0 or -1, the number of times the file system is mounted will be disregarded by e2fsck(8) and the kernel. Staggering the mount-counts at which file systems are forcibly checked will avoid all file systems being checked at one time when using journaled file systems. Mount-count-dependent checking is disabled by default to avoid unanticipated long re‐ boots while e2fsck does its work. If you are concerned about file system corruptions caused by potential hardware problems of kernel bugs, a better solution than mount- count-dependent checking is to use the e2scrub(8) program. This does require placing the file system on an LVM volume, however."
        },
        {
            "flag": "-C",
            "long": null,
            "arg": null,
            "description": "Set the number of times the file system has been mounted. If set to a greater value than the max-mount-counts parameter set by the -c option, e2fsck(8) will check the file system at the next reboot."
        },
        {
            "flag": "-e",
            "long": null,
            "arg": null,
            "description": "Change the behavior of the kernel code when errors are detected. In all cases, a file system error will cause e2fsck(8) to check the file system on the next boot. error- behavior can be one of the following: continue Continue normal execution. remount-ro Remount file system read-only. panic Cause a kernel panic."
        },
        {
            "flag": "-E",
            "long": null,
            "arg": null,
            "description": "Set extended options for the file system. Extended options are comma separated, and may take an argument using the equals ('=') sign. The following extended options are supported: clearmmp Reset the MMP block (if any) back to the clean state. Use only if abso‐ lutely certain the device is not currently mounted or being fscked, or ma‐ jor file system corruption can result. Needs '-f'. mmpupdateinterval=interval Adjust the initial MMP update interval to interval seconds. Specifying an interval of 0 means to use the default interval. The specified interval must be less than 300 seconds. Requires that the mmp feature be enabled. stride=stride-size Configure the file system for a RAID array with stride-size file system blocks. This is the number of blocks read or written to disk before moving to next disk. This mostly affects placement of file system metadata like bitmaps at mke2fs(2) time to avoid placing them on a single disk, which can hurt the performance. It may also be used by block allocator. stripewidth=stripe-width Configure the file system for a RAID array with stripe-width file system blocks per stripe. This is typically be stride-size * N, where N is the number of data disks in the RAID (e.g. RAID 5 N+1, RAID 6 N+2). This al‐ lows the block allocator to prevent read-modify-write of the parity in a RAID stripe if possible when the data is written. hashalg=hash-alg Set the default hash algorithm used for file systems with hashed b-tree directories. Valid algorithms accepted are: legacy, halfmd4, and tea. encoding=encoding-name Enable the casefold feature in the super block and set encoding-name as the encoding to be used. If encoding-name is not specified, utf8 is used. The encoding cannot be altered if casefold was previously enabled. encodingflags=encoding-flags Define parameters for file name character encoding operations. If a flag is not changed using this parameter, its default value is used. encoding- flags should be a comma-separated lists of flags to be enabled. The flags cannot be altered if casefold was previously enabled. The only flag that can be set right now is strict which means that invalid strings should be rejected by the file system. In the default configura‐ tion, the strict flag is disabled. mountopts=mountoptionstring Set a set of default mount options which will be used when the file system is mounted. Unlike the bitmask-based default mount options which can be specified with the -o option, mountoptionstring is an arbitrary string with a maximum length of 63 bytes, which is stored in the superblock. The ext4 file system driver will first apply the bitmask-based default op‐ tions, and then parse the mountoptionstring, before parsing the mount options passed from the mount(8) program. This superblock setting is only honored in 2.6.35+ kernels; and not at all by the ext2 and ext3 file system drivers. forcefsck Set a flag in the file system superblock indicating that errors have been found. This will force fsck to run at the next mount. testfs Set a flag in the file system superblock indicating that it may be mounted using experimental kernel code, such as the ext4dev file system. ^testfs Clear the testfs flag, indicating the file system should only be mounted using production-level file system code."
        },
        {
            "flag": "-f",
            "long": null,
            "arg": null,
            "description": "useful when removing the hasjournal file system feature from a file system which has an external journal (or is corrupted such that it appears to have an external jour‐ nal), but that external journal is not available. If the file system appears to re‐ quire journal replay, the -f flag must be specified twice to proceed. WARNING: Removing an external journal from a file system which was not cleanly un‐ mounted without first replaying the external journal can result in severe data loss and file system corruption."
        },
        {
            "flag": "-g",
            "long": null,
            "arg": null,
            "description": "Set the group which can use the reserved file system blocks. The group parameter can be a numerical gid or a group name. If a group name is given, it is converted to a numerical gid before it is stored in the superblock."
        },
        {
            "flag": "-i",
            "long": null,
            "arg": null,
            "description": "Adjust the maximal time between two file system checks. No suffix or d will interpret the number interval-between-checks as days, m as months, and w as weeks. A value of zero will disable the time-dependent checking. There are pros and cons to disabling these periodic checks; see the discussion under the -c (mount-count-dependent check) option for details."
        },
        {
            "flag": "-I",
            "long": null,
            "arg": null,
            "description": "ble, so it requires that the file system is checked for consistency first using e2fsck(8). This operation can also take a while and the file system can be corrupted and data lost if it is interrupted while in the middle of converting the file system. Backing up the file system before changing inode size is recommended. File systems with an inode size of 128 bytes do not support timestamps beyond January 19, 2038. Inodes which are 256 bytes or larger will support extended timestamps, project id's, and the ability to store some extended attributes in the inode table for improved performance."
        },
        {
            "flag": "-J",
            "long": null,
            "arg": null,
            "description": "fault journal parameters will be used to create an appropriately sized journal (given the size of the file system) stored within the file system. Note that you must be us‐ ing a kernel which has ext3 support in order to actually make use of the journal. If this option is used to create a journal on a mounted file system, an immutable file, .journal, will be created in the top-level directory of the file system, as it is the only safe way to create the journal inode while the file system is mounted. While the ext3 journal is visible, it is not safe to delete it, or modify it while the file system is mounted; for this reason the file is marked immutable. While checking unmounted file systems, e2fsck(8) will automatically move .journal files to the invis‐ ible, reserved journal inode. For all file systems except for the root file system, this should happen automatically and naturally during the next reboot cycle. Since the root file system is mounted read-only, e2fsck(8) must be run from a rescue floppy in order to effect this transition. On some distributions, such as Debian, if an initial ramdisk is used, the initrd scripts will automatically convert an ext2 root file system to ext3 if the /etc/fstab file specifies the ext3 file system for the root file system in order to avoid requir‐ ing the use of a rescue floppy to add an ext3 journal to the root file system."
        },
        {
            "flag": "-J",
            "long": null,
            "arg": null,
            "description": "Override the default ext3 journal parameters. Journal options are comma separated, and may take an argument using the equals ('=') sign. The following journal options are supported: size=journal-size Create a journal stored in the file system of size journal-size megabytes. The size of the journal must be at least 1024 file system blocks (i.e., 1MB if using 1k blocks, 4MB if using 4k blocks, etc.) and may be no more than 10,240,000 file system blocks. There must be enough free space in the file system to create a journal of that size. fastcommitsize=fast-commit-size Create an additional fast commit journal area of size fast-commit-size kilobytes. This option is only valid if fastcommit feature is enabled on the file system. If this option is not specified and if fastcommit fea‐ ture is turned on, fast commit area size defaults to journal-size / 64 megabytes. The total size of the journal with fastcommit feature set is journal-size + ( fast-commit-size * 1024) megabytes. The total journal size may be no more than 10,240,000 file system blocks or half the total file system size (whichever is smaller). location=journal-location Specify the location of the journal. The argument journal-location can either be specified as a block number, or if the number has a units suffix (e.g., 'M', 'G', etc.) interpret it as the offset from the beginning of the file system. device=external-journal Attach the file system to the journal block device located on external- journal. The external journal must have been already created using the command mke2fs -O journaldev external-journal Note that external-journal must be formatted with the same block size as file systems which will be using it. In addition, while there is support for attaching multiple file systems to a single external journal, the Linux kernel and e2fsck(8) do not currently support shared external jour‐ nals yet. Instead of specifying a device name directly, external-journal can also be specified by either LABEL=label or UUID=UUID to locate the external jour‐ nal by either the volume label or UUID stored in the ext2 superblock at the start of the journal. Use dumpe2fs(8) to display a journal device's volume label and UUID. See also the -L option of tune2fs(8). Only one of the size or device options can be given for a file system."
        },
        {
            "flag": "-l",
            "long": null,
            "arg": null,
            "description": "parameters that can be set via this program."
        },
        {
            "flag": "-L",
            "long": null,
            "arg": null,
            "description": "Set the volume label of the file system. Ext2 file system labels can be at most 16 characters long; if volume-label is longer than 16 characters, tune2fs will truncate it and print a warning. The volume label can be used by mount(8), fsck(8), and /etc/fstab(5) (and possibly others) by specifying LABEL=volume-label instead of a block special device name like /dev/hda5."
        },
        {
            "flag": "-m",
            "long": null,
            "arg": null,
            "description": "Set the percentage of the file system which may only be allocated by privileged pro‐ cesses. Reserving some number of file system blocks for use by privileged processes is done to avoid file system fragmentation, and to allow system daemons, such as sys‐‐ logd(8), to continue to function correctly after non-privileged processes are pre‐ vented from writing to the file system. Normally, the default percentage of reserved blocks is 5%."
        },
        {
            "flag": "-M",
            "long": null,
            "arg": null,
            "description": "Set the last-mounted directory for the file system."
        },
        {
            "flag": "-o",
            "long": null,
            "arg": null,
            "description": "Set or clear the indicated default mount options in the file system. Default mount options can be overridden by mount options specified either in /etc/fstab(5) or on the command line arguments to mount(8). Older kernels may not support this feature; in particular, kernels which predate 2.4.20 will almost certainly ignore the default mount options field in the superblock. More than one mount option can be cleared or set by separating features with commas. Mount options prefixed with a caret character ('^') will be cleared in the file sys‐ tem's superblock; mount options without a prefix character or prefixed with a plus character ('+') will be added to the file system. The following mount options can be set or cleared using tune2fs: debug Enable debugging code for this file system. bsdgroups Emulate BSD behavior when creating new files: they will take the group-id of the directory in which they were created. The standard System V behav‐ ior is the default, where newly created files take on 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. userxattr Enable user-specified extended attributes. acl Enable Posix Access Control Lists. uid16 Disables 32-bit UIDs and GIDs. This is for interoperability with older kernels which only store and expect 16-bit values. journaldata When the file system is mounted with journaling enabled, all data (not just metadata) is committed into the journal prior to being written into the main file system. journaldataordered When the file system is mounted with journaling enabled, all data is forced directly out to the main file system prior to its metadata being committed to the journal. journaldatawriteback When the file system is mounted with journaling enabled, data may be writ‐ ten into the main file system after its metadata has been committed to the journal. This may increase throughput, however, it may allow old data to appear in files after a crash and journal recovery. nobarrier The file system will be mounted with barrier operations in the journal disabled. (This option is currently only supported by the ext4 file sys‐ tem driver in 2.6.35+ kernels.) blockvalidity The file system will be mounted with the blockvalidity option enabled, which causes extra checks to be performed after reading or writing from the file system. This prevents corrupted metadata blocks from causing file system damage by overwriting parts of the inode table or block group descriptors. This comes at the cost of increased memory and CPU overhead, so it is enabled only for debugging purposes. (This option is currently only supported by the ext4 file system driver in 2.6.35+ kernels.) discard The file system will be mounted with the discard mount option. This will cause the file system driver to attempt to use the trim/discard feature of some storage devices (such as SSD's and thin-provisioned drives available in some enterprise storage arrays) to inform the storage device that blocks belonging to deleted files can be reused for other purposes. (This option is currently only supported by the ext4 file system driver in 2.6.35+ kernels.) nodelalloc The file system will be mounted with the nodelalloc mount option. This will disable the delayed allocation feature. (This option is currently only supported by the ext4 file system driver in 2.6.35+ kernels.)"
        },
        {
            "flag": "-O",
            "long": null,
            "arg": null,
            "description": "Set or clear the indicated file system features (options) in the file system. More than one file system feature can be cleared or set by separating features with commas. File System features prefixed with a caret character ('^') will be cleared in the file system's superblock; file system features without a prefix character or prefixed with a plus character ('+') will be added to the file system. For a detailed description of the file system features, please see the man page ext4(5). The following file system features can be set or cleared using tune2fs: 64bit Enable the file system to be larger than 2^32 blocks. casefold Enable support for file system level casefolding. Tune2fs currently only supports setting this file system feature. dirindex Use hashed b-trees to speed up lookups for large directories. dirnlink Allow more than 65000 subdirectories per directory. eainode Allow the value of each extended attribute to be placed in the data blocks of a separate inode if necessary, increasing the limit on the size and number of extended attributes per file. Tune2fs currently only supports setting this file system feature. encrypt Enable support for file system level encryption. Tune2fs currently only supports setting this file system feature. extent Enable the use of extent trees to store the location of data blocks in in‐ odes. Tune2fs currently only supports setting this file system feature. extraisize Enable the extended inode fields used by ext4. filetype Store file type information in directory entries. flexbg Allow bitmaps and inode tables for a block group to be placed anywhere on the storage media. Tune2fs will not reorganize the location of the inode tables and allocation bitmaps, as mke2fs(8) will do when it creates a freshly formatted file system with flexbg enabled. hasjournal Use a journal to ensure file system consistency even across unclean shut‐ downs. Setting the file system feature is equivalent to using the -j op‐ tion. fastcommit Enable fast commit journaling feature to improve fsync latency. largedir Increase the limit on the number of files per directory. Tune2fs cur‐ rently only supports setting this file system feature. hugefile Support files larger than 2 terabytes in size. largefile File System can contain files that are greater than 2GB. metadatacsum Store a checksum to protect the contents in each metadata block. metadatacsumseed Allow the file system to store the metadata checksum seed in the su‐ perblock, enabling the administrator to change the UUID of a file system using the metadatacsum feature while it is mounted. mmp Enable or disable multiple mount protection (MMP) feature. project Enable project ID tracking. This is used for project quota tracking. quota Enable internal file system quota inodes. read-only Force the kernel to mount the file system read-only. resizeinode Reserve space so the block group descriptor table may grow in the future. Tune2fs only supports clearing this file system feature. sparsesuper Limit the number of backup superblocks to save space on large file sys‐ tems. Tune2fs currently only supports setting this file system feature. stableinodes Prevent the file system from being shrunk or having its UUID changed, in order to allow the use of specialized encryption settings that make use of the inode numbers and UUID. Tune2fs currently only supports setting this file system feature. uninitbg Allow the kernel to initialize bitmaps and inode tables lazily, and to keep a high watermark for the unused inodes in a file system, to reduce e2fsck(8) time. The first e2fsck run after enabling this feature will take the full time, but subsequent e2fsck runs will take only a fraction of the original time, depending on how full the file system is. verity Enable support for verity protected files. Tune2fs currently only sup‐ ports setting this file system feature. After setting or clearing sparsesuper, uninitbg, filetype, or resizeinode file sys‐ tem features, the file system may require being checked using e2fsck(8) to return the file system to a consistent state. Tune2fs will print a message requesting that the system administrator run e2fsck(8) if necessary. After setting the dirindex feature, e2fsck -D can be run to convert existing directories to the hashed B-tree format. En‐ abling certain file system features may prevent the file system from being mounted by kernels which do not support those features. In particular, the uninitbg and flexbg features are only supported by the ext4 file system."
        },
        {
            "flag": "-r",
            "long": null,
            "arg": null,
            "description": "Set the number of reserved file system blocks."
        },
        {
            "flag": "-Q",
            "long": null,
            "arg": null,
            "description": "Sets 'quota' feature on the superblock and works on the quota files for the given quota type. Quota options could be one or more of the following: [^]usrquota Sets/clears user quota inode in the superblock. [^]grpquota Sets/clears group quota inode in the superblock. [^]prjquota Sets/clears project quota inode in the superblock."
        },
        {
            "flag": "-T",
            "long": null,
            "arg": null,
            "description": "Set the time the file system was last checked using e2fsck. The time is interpreted using the current (local) timezone. This can be useful in scripts which use a Logical Volume Manager to make a consistent snapshot of a file system, and then check the file system during off hours to make sure it hasn't been corrupted due to hardware prob‐ lems, etc. If the file system was clean, then this option can be used to set the last checked time on the original file system. The format of time-last-checked is the in‐ ternational date format, with an optional time specifier, i.e. YYYYMMDD[HH[MM[SS]]]. The keyword now is also accepted, in which case the last checked time will be set to the current time."
        },
        {
            "flag": "-u",
            "long": null,
            "arg": null,
            "description": "Set the user who can use the reserved file system blocks. user can be a numerical uid or a user name. If a user name is given, it is converted to a numerical uid before it is stored in the superblock."
        },
        {
            "flag": "-U",
            "long": null,
            "arg": null,
            "description": "Set the universally unique identifier (UUID) of the file system to UUID. The format of the UUID is a series of hex digits separated by hyphens, like this: \"c1b9d5a2-f162-11cf-9ece-0020afc76f16\". The UUID parameter may also be one of the following: clear clear the file system UUID random generate a new randomly-generated UUID time generate a new time-based UUID The UUID may be used by mount(8), fsck(8), and /etc/fstab(5) (and possibly others) by specifying UUID=uuid instead of a block special device name like /dev/hda1. See uuidgen(8) for more information. If the system does not have a good random number generator such as /dev/random or /dev/urandom, tune2fs will automatically use a time- based UUID instead of a randomly-generated UUID."
        },
        {
            "flag": "-z",
            "long": null,
            "arg": null,
            "description": "Before overwriting a file system block, write the old contents of the block to an undo file. This undo file can be used with e2undo(8) to restore the old contents of the file system should something go wrong. If the empty string is passed as the undofile argument, the undo file will be written to a file named tune2fs-device.e2undo in the directory specified via the E2FSPROGSUNDODIR environment variable. WARNING: The undo file cannot be used to recover from a power or system crash."
        }
    ],
    "examples": [],
    "see_also": [
        {
            "name": "debugfs",
            "section": "8",
            "url": "https://www.chedong.com/phpMan.php/man/debugfs/8/json"
        },
        {
            "name": "dumpe2fs",
            "section": "8",
            "url": "https://www.chedong.com/phpMan.php/man/dumpe2fs/8/json"
        },
        {
            "name": "e2fsck",
            "section": "8",
            "url": "https://www.chedong.com/phpMan.php/man/e2fsck/8/json"
        },
        {
            "name": "mke2fs",
            "section": "8",
            "url": "https://www.chedong.com/phpMan.php/man/mke2fs/8/json"
        },
        {
            "name": "ext4",
            "section": "5",
            "url": "https://www.chedong.com/phpMan.php/man/ext4/5/json"
        }
    ]
}