-c

Adjust the number of mounts after which the filesystem will be checked by e2fsck(8). If max-mount-counts is 0 or -1, the number of times the filesystem is mounted will be disregarded by e2fsck(8) andthe kernel.Staggering the mount-counts at which filesystems are forcibly checked will avoid all filesystems beingchecked at one time when using journaled filesystems.Mount-count-dependent checking is disabled by default to avoid unanticipated long reboots while e2fsckdoes its work. However, you may wish to consider the consequences of disabling mount-count-dependentchecking entirely. Bad disk drives, cables, memory, and kernel bugs could all corrupt a filesystemwithout marking the filesystem dirty or in error. If you are using journaling on your filesystem, yourfilesystem will never be marked dirty, so it will not normally be checked. A filesystem error detectedby the kernel will still force an fsck on the next reboot, but it may already be too late to preventdata loss at that point.See also the -i option for time-dependent checking.

-C

Set the number of times the filesystem 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 filesystem at the next reboot.

-e

Change the behavior of the kernel code when errors are detected. In all cases, a filesystem error willcause e2fsck(8) to check the filesystem on the next boot. error-behavior can be one of the following:continue Continue normal execution.remount-ro Remount filesystem read-only.panic Cause a kernel panic.

-E

Set extended options for the filesystem. Extended options are comma separated, and may take an argu‐ment using the equals ('=') sign. The following extended options are supported:clear_mmpReset the MMP block (if any) back to the clean state. Use only if absolutely certain thedevice is not currently mounted or being fscked, or major filesystem corruption can result.Needs '-f'.mmp_update_interval=intervalAdjust the initial MMP update interval to interval seconds. Specifying an interval of 0means to use the default interval. The specified interval must be less than 300 seconds.Requires that the mmp feature be enabled.stride=stride-sizeConfigure the filesystem for a RAID array with stride-size filesystem blocks. This is thenumber of blocks read or written to disk before moving to next disk. This mostly affectsplacement of filesystem metadata like bitmaps at mke2fs(2) time to avoid placing them on asingle disk, which can hurt the performance. It may also be used by block allocator.stripe_width=stripe-widthConfigure the filesystem for a RAID array with stripe-width filesystem 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 allows the block allocator to prevent read-modify-write ofthe parity in a RAID stripe if possible when the data is written.hash_alg=hash-algSet the default hash algorithm used for filesystems with hashed b-tree directories. Validalgorithms accepted are: legacy, half_md4, and tea.mount_opts=mount_option_stringSet 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,mount_option_string is an arbitrary string with a maximum length of 63 bytes, which isstored in the superblock.The ext4 file system driver will first apply the bitmask-based default options, and thenparse the mount_option_string, 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 andext3 file system drivers.test_fsSet a flag in the filesystem superblock indicating that it may be mounted using experimen‐tal kernel code, such as the ext4dev filesystem.^test_fsClear the test_fs flag, indicating the filesystem should only be mounted using production-level filesystem code.

-g

Set the group which can use the reserved filesystem blocks. The group parameter can be a numerical gidor a group name. If a group name is given, it is converted to a numerical gid before it is stored inthe superblock.

-i

Adjust the maximal time between two filesystem checks. No suffix or d will interpret the number inter‐val-between-checks as days, m as months, and w as weeks. A value of zero will disable the time-depen‐dent checking.There are pros and cons to disabling these periodic checks; see the discussion under the -c (mount-count-dependent check) option for details.

-J

Override the default ext3 journal parameters. Journal options are comma separated, and may take anargument using the equals ('=') sign. The following journal options are supported:size=journal-sizeCreate a journal stored in the filesystem of size journal-size megabytes. The size of thejournal must be at least 1024 filesystem blocks (i.e., 1MB if using 1k blocks, 4MB if using4k blocks, etc.) and may be no more than 10,240,000 filesystem blocks. There must beenough free space in the filesystem to create a journal of that size.location=journal-locationSpecify the location of the journal. The argument journal-location can either be specifiedas a block number, or if the number has a units suffix (e.g., 'M', 'G', etc.) interpret itas the offset from the beginning of the file system.device=external-journalAttach the filesystem to the journal block device located on external-journal. The exter‐nal journal must have been already created using the commandmke2fs -O journal_dev external-journalNote that external-journal must be formatted with the same block size as filesystems whichwill be using it. In addition, while there is support for attaching multiple filesystemsto a single external journal, the Linux kernel and e2fsck(8) do not currently supportshared external journals yet.Instead of specifying a device name directly, external-journal can also be specified byeither LABEL=label or UUID=UUID to locate the external journal by either the volume labelor UUID stored in the ext2 superblock at the start of the journal. Use dumpe2fs(8) to dis‐play 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 filesystem.

-L

Set the volume label of the filesystem. Ext2 filesystem labels can be at most 16 characters long; ifvolume-label is longer than 16 characters, tune2fs will truncate it and print a warning. The volumelabel can be used by mount(8), fsck(8), and /etc/fstab(5) (and possibly others) by specifyingLABEL=volume-label instead of a block special device name like /dev/hda5.

-m

Set the percentage of the filesystem which may only be allocated by privileged processes. Reservingsome number of filesystem blocks for use by privileged processes is done to avoid filesystem fragmenta‐tion, and to allow system daemons, such as syslogd(8), to continue to function correctly after non-privileged processes are prevented from writing to the filesystem. Normally, the default percentage ofreserved blocks is 5%.

-M

Set the last-mounted directory for the filesystem.

-o

Set or clear the indicated default mount options in the filesystem. Default mount options can be over‐ridden 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 almostcertainly 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 optionsprefixed with a caret character ('^') will be cleared in the filesystem's superblock; mount optionswithout a prefix character or prefixed with a plus character ('+') will be added to the filesystem.The following mount options can be set or cleared using tune2fs:debug Enable debugging code for this filesystem.bsdgroupsEmulate BSD behavior when creating new files: they will take the group-id of the directoryin which they were created. The standard System V behavior is the default, where newlycreated files take on the fsgid of the current process, unless the directory has the setgidbit set, in which case it takes the gid from the parent directory, and also gets the setgidbit set if it is a directory itself.user_xattrEnable 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 onlystore and expect 16-bit values.journal_dataWhen the filesystem is mounted with journalling enabled, all data (not just metadata) iscommitted into the journal prior to being written into the main filesystem.journal_data_orderedWhen the filesystem is mounted with journalling enabled, all data is forced directly out tothe main file system prior to its metadata being committed to the journal.journal_data_writebackWhen the filesystem is mounted with journalling enabled, data may be written into the mainfilesystem after its metadata has been committed to the journal. This may increasethroughput, however, it may allow old data to appear in files after a crash and journalrecovery.nobarrierThe file system will be mounted with barrier operations in the journal disabled. (Thisoption is currently only supported by the ext4 file system driver in 2.6.35+ kernels.)block_validityThe file system will be mounted with the block_validity option enabled, which causes extrachecks to be performed after reading or writing from the file system. This prevents cor‐rupted metadata blocks from causing file system damage by overwriting parts of the inodetable or block group descriptors. This comes at the cost of increased memory and CPU over‐head, so it is enabled only for debugging purposes. (This option is currently only sup‐ported by the ext4 file system driver in 2.6.35+ kernels.)discardThe file system will be mounted with the discard mount option. This will cause the filesystem driver to attempt to use the trim/discard feature of some storage devices (such asSSD's and thin-provisioned drives available in some enterprise storage arrays) to informthe 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+ ker‐nels.)nodelallocThe file system will be mounted with the nodelalloc mount option. This will disable thedelayed allocation feature. (This option is currently only supported by the ext4 file sys‐tem driver in 2.6.35+ kernels.)

-O

Set or clear the indicated filesystem features (options) in the filesystem. More than one filesystemfeature can be cleared or set by separating features with commas. Filesystem features prefixed with acaret character ('^') will be cleared in the filesystem's superblock; filesystem features without aprefix character or prefixed with a plus character ('+') will be added to the filesystem. For adetailed description of the file system features, please see the man page ext4(5).The following filesystem features can be set or cleared using tune2fs:64bit Enable the file system to be larger than 2^32 blocks.dir_indexUse hashed b-trees to speed up lookups for large directories.dir_nlinkAllow more than 65000 subdirectories per directory.ea_inodeAllow the value of each extended attribute to be placed in the data blocks of a separateinode if necessary, increasing the limit on the size and number of extended attributes perfile. Tune2fs currently only supports setting this filesystem feature.encryptEnable file system level encryption. Tune2fs currently only supports setting this filesys‐tem feature.extent Enable the use of extent trees to store the location of data blocks in inodes. Tune2fscurrently only supports setting this filesystem feature.extra_isizeEnable the extended inode fields used by ext4.filetypeStore file type information in directory entries.flex_bgAllow bitmaps and inode tables for a block group to be placed anywhere on the storagemedia. Tune2fs will not reorganize the location of the inode tables and allocation bit‐maps, as mke2fs(8) will do when it creates a freshly formatted file system with flex_bgenabled.has_journalUse a journal to ensure filesystem consistency even across unclean shutdowns. Setting thefilesystem feature is equivalent to using the -j option.large_dirIncrease the limit on the number of files per directory. Tune2fs currently only supportssetting this filesystem feature.huge_fileSupport files larger than 2 terabytes in size.large_fileFilesystem can contain files that are greater than 2GB.metadata_csumStore a checksum to protect the contents in each metadata block.metadata_csum_seedAllow the filesystem to store the metadata checksum seed in the superblock, enabling theadministrator to change the UUID of a filesystem using the metadata_csum feature while itis mounted.mmp Enable or disable multiple mount protection (MMP) feature.projectEnable project ID tracking. This is used for project quota tracking.quota Enable internal file system quota inodes.read-onlyForce the kernel to mount the file system read-only.resize_inodeReserve space so the block group descriptor table may grow in the future. Tune2fs onlysupports clearing this filesystem feature.sparse_superLimit the number of backup superblocks to save space on large filesystems. Tune2fs cur‐rently only supports setting this filesystem feature.uninit_bgAllow the kernel to initialize bitmaps and inode tables lazily, and to keep a high water‐mark for the unused inodes in a filesystem, to reduce e2fsck(8) time. The first e2fsck runafter enabling this feature will take the full time, but subsequent e2fsck runs will takeonly a fraction of the original time, depending on how full the file system is.After setting or clearing sparse_super, uninit_bg, filetype, or resize_inode filesystem features, thefile system may require being checked using e2fsck(8) to return the filesystem to a consistent state.Tune2fs will print a message requesting that the system administrator run e2fsck(8) if necessary.After setting the dir_index feature, e2fsck -D can be run to convert existing directories to the hashed

-r

Set the number of reserved filesystem blocks.

-Q

Sets 'quota' feature on the superblock and works on the quota files for the given quota type. Quotaoptions could be one or more of the following:[^]usrquotaSets/clears user quota inode in the superblock.[^]grpquotaSets/clears group quota inode in the superblock.[^]prjquotaSets/clears project quota inode in the superblock.

-T

Set the time the filesystem 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 consis‐tent snapshot of a filesystem, and then check the filesystem during off hours to make sure it hasn'tbeen corrupted due to hardware problems, etc. If the filesystem was clean, then this option can beused to set the last checked time on the original filesystem. The format of time-last-checked is theinternational date format, with an optional time specifier, i.e. YYYYMMDD[HH[MM[SS]]]. The keywordnow is also accepted, in which case the last checked time will be set to the current time.

-u

Set the user who can use the reserved filesystem 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.

-U

Set the universally unique identifier (UUID) of the filesystem to UUID. The format of the UUID is aseries of hex digits separated by hyphens, like this: "c1b9d5a2-f162-11cf-9ece-0020afc76f16". The UUIDparameter may also be one of the following:clear clear the filesystem UUIDrandom generate a new randomly-generated UUIDtime generate a new time-based UUIDThe UUID may be used by mount(8), fsck(8), and /etc/fstab(5) (and possibly others) by specifyingUUID=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 suchas /dev/random or /dev/urandom, tune2fs will automatically use a time-based UUID instead of a randomly-generated UUID.

-z

Before overwriting a file system block, write the old contents of the block to an undo file. This undofile can be used with e2undo(8) to restore the old contents of the file system should something gowrong. If the empty string is passed as the undo_file argument, the undo file will be written to afile named tune2fs-device.e2undo in the directory specified via the E2FSPROGS_UNDO_DIR environmentvariable.WARNING: The undo file cannot be used to recover from a power or system crash.BUGSWe haven't found any bugs yet. That doesn't mean there aren't any...AUTHORtune2fs was written by Remy Card <Remy.Card@linux.org>. It is currently being maintained by Theodore Ts'o<tytso@alum.mit.edu>. tune2fs uses the ext2fs library written by Theodore Ts'o <tytso@mit.edu>. This manualpage was written by Christian Kuhtz <chk@data-hh.Hanse.DE>. Time-dependent checking was added by Uwe Ohse<uwe@tirka.gun.de>.AVAILABILITYtune2fs is part of the e2fsprogs package and is available from http://e2fsprogs.sourceforge.net.