TUNE2FS(8) System Manager's Manual TUNE2FS(8)
NAME
tune2fs - adjust tunable filesystem parameters on ext2/ext3/ext4 filesystems
SYNOPSIS
tune2fs [ -l ] [ -c max-mount-counts ] [ -e errors-behavior ] [ -f ] [ -i interval-between-checks ] [ -j ] [
-J journal-options ] [ -m reserved-blocks-percentage ] [ -o [^]mount-options[,...] ] [ -r reserved-blocks-
count ] [ -s sparse-super-flag ] [ -u user ] [ -g group ] [ -C mount-count ] [ -E extended-options ] [ -L vol‐
ume-name ] [ -M last-mounted-directory ] [ -O [^]feature[,...] ] [ -Q quota-options ] [ -T time-last-checked
] [ -U UUID ] device
DESCRIPTION
tune2fs allows the system administrator to adjust various tunable filesystem parameters on Linux ext2, ext3,
or ext4 filesystems. The current values of these options can be displayed by using the -l option to
tune2fs(8) program, or by using the dumpe2fs(8) program.
The device specifier can either be a filename (i.e., /dev/sda1), or a LABEL or UUID specifier: "LABEL=volume-
name" or "UUID=uuid". (i.e., LABEL=home or UUID=e40486c6-84d5-4f2f-b99c-032281799c9d).
OPTIONS
-c max-mount-counts
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) and
the kernel.
Staggering the mount-counts at which filesystems are forcibly checked will avoid all filesystems being
checked at one time when using journaled filesystems.
You should strongly consider the consequences of disabling mount-count-dependent checking entirely.
Bad disk drives, cables, memory, and kernel bugs could all corrupt a filesystem without marking the
filesystem dirty or in error. If you are using journaling on your filesystem, your filesystem will
never be marked dirty, so it will not normally be checked. A filesystem error detected by the kernel
will still force an fsck on the next reboot, but it may already be too late to prevent data loss at
that point.
See also the -i option for time-dependent checking.
-C mount-count
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 error-behavior
Change the behavior of the kernel code when errors are detected. In all cases, a filesystem error will
cause 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 extended-options
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_mmp
Reset the MMP block (if any) back to the clean state. Use only if absolutely certain the
single disk, which can hurt the performance. It may also be used by block allocator.
stripe_width=stripe-width
Configure 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 of
the parity in a RAID stripe if possible when the data is written.
hash_alg=hash-alg
Set the default hash algorithm used for filesystems with hashed b-tree directories. Valid
algorithms accepted are: legacy, half_md4, and tea.
mount_opts=mount_option_string
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,
mount_option_string 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 options, and then
parse 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 and
ext3 file system drivers.
test_fs
Set a flag in the filesystem superblock indicating that it may be mounted using experimen‐
tal kernel code, such as the ext4dev filesystem.
^test_fs
Clear the test_fs flag, indicating the filesystem should only be mounted using production-
level filesystem code.
-f Force the tune2fs operation to complete even in the face of errors. This option is useful when remov‐
ing the has_journal filesystem feature from a filesystem which has an external journal (or is corrupted
such that it appears to have an external journal), but that external journal is not available. If the
filesystem appears to require journal replay, the -f flag must be specified twice to proceed.
WARNING: Removing an external journal from a filesystem which was not cleanly unmounted without first
replaying the external journal can result in severe data loss and filesystem corruption.
-g group
Set the group which can use the reserved filesystem 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.
-i interval-between-checks[d|m|w]
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.
It is strongly recommended that either -c (mount-count-dependent) or -i (time-dependent) checking be
enabled to force periodic full e2fsck(8) checking of the filesystem. Failure to do so may lead to
filesystem corruption (due to bad disks, cables, memory, or kernel bugs) going unnoticed, ultimately
reserved journal inode. For all filesystems except for the root filesystem, this should happen auto‐
matically and naturally during the next reboot cycle. Since the root filesystem 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 automati‐
cally convert an ext2 root filesystem to ext3 if the /etc/fstab file specifies the ext3 filesystem for
the root filesystem in order to avoid requiring the use of a rescue floppy to add an ext3 journal to
the root filesystem.
-J journal-options
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 filesystem of size journal-size megabytes. The size of the
journal must be at least 1024 filesystem blocks (i.e., 1MB if using 1k blocks, 4MB if using
4k blocks, etc.) and may be no more than 102,400 filesystem blocks. There must be enough
free space in the filesystem to create a journal of that size.
device=external-journal
Attach the filesystem to the journal block device located on external-journal. The exter‐
nal journal must have been already created using the command
mke2fs -O journal_dev external-journal
Note that external-journal must be formatted with the same block size as filesystems which
will be using it. In addition, while there is support for attaching multiple filesystems
to a single external journal, the Linux kernel and e2fsck(8) do not currently support
shared external journals 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 journal by either the volume label
or 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 List the contents of the filesystem superblock, including the current values of the parameters that can
be set via this program.
-L volume-label
Set the volume label of the filesystem. Ext2 filesystem 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.
-m reserved-blocks-percentage
Set the percentage of the filesystem which may only be allocated by privileged processes. Reserving
some 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 of
reserved blocks is 5%.
-M last-mounted-directory
The following mount options can be set or cleared using tune2fs:
debug Enable debugging code for this filesystem.
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 behavior 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.
user_xattr
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.
journal_data
When the filesystem is mounted with journalling enabled, all data (not just metadata) is
committed into the journal prior to being written into the main filesystem.
journal_data_ordered
When the filesystem is mounted with journalling enabled, all data is forced directly out to
the main file system prior to its metadata being committed to the journal.
journal_data_writeback
When the filesystem is mounted with journalling enabled, data may be written into the main
filesystem 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 system driver in 2.6.35+ kernels.)
block_validity
The file system will be mounted with the block_validity option enabled, which causes extra
checks 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 inode
table 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.)
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+ ker‐
nels.)
nodelalloc
dir_index
Use hashed b-trees to speed up lookups for large directories.
dir_nlink
Allow more than 65000 subdirectories per directory.
extent Enable the use of extent trees to store the location of data blocks in inodes.
extra_isize
Enable the extended inode fields used by ext4.
filetype
Store file type information in directory entries.
flex_bg
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 bit‐
maps, as mke2fs(8) will do when it creates a freshly formatted file system with flex_bg
enabled.
has_journal
Use a journal to ensure filesystem consistency even across unclean shutdowns. Setting the
filesystem feature is equivalent to using the -j option.
huge_file
Support files larger than 2 terabytes in size.
large_file
Filesystem can contain files that are greater than 2GB.
resize_inode
Reserve space so the block group descriptor table may grow in the future. Tune2fs only
supports clearing this filesystem feature.
mmp Enable or disable multiple mount protection (MMP) feature.
sparse_super
Limit the number of backup superblocks to save space on large filesystems.
uninit_bg
Allow 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. This 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.
After setting or clearing sparse_super, uninit_bg, filetype, or resize_inode filesystem features,
e2fsck(8) must be run on the filesystem 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 B-tree format.
Enabling certain filesystem features may prevent the filesystem from being mounted by kernels which do
not support those features. In particular, the uninit_bg and flex_bg features are only supported by
the ext4 filesystem.
[^]grpquota
Sets/clears group quota inode in the superblock.
-T time-last-checked
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't
been corrupted due to hardware problems, etc. If the filesystem was clean, then this option can be
used to set the last checked time on the original filesystem. The format of time-last-checked is the
international 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.
-u user
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 UUID
Set the universally unique identifier (UUID) of the filesystem 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 filesystem 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.
BUGS
We haven't found any bugs yet. That doesn't mean there aren't any...
AUTHOR
tune2fs was written by Remy Card <[email protected]>. It is currently being maintained by Theodore Ts'o
<[email protected]>. tune2fs uses the ext2fs library written by Theodore Ts'o <[email protected]>. This manual
page was written by Christian Kuhtz <[email protected]>. Time-dependent checking was added by Uwe Ohse
<[email protected]>.
AVAILABILITY
tune2fs is part of the e2fsprogs package and is available from http://e2fsprogs.sourceforge.net.
SEE ALSO
debugfs(8), dumpe2fs(8), e2fsck(8), mke2fs(8), ext4(5)
E2fsprogs version 1.42.9 December 2013 TUNE2FS(8)
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