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 volume-name ] [ -M
last-mounted-directory ] [ -O [^]feature[,...] ] [ -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.
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 argument using the equals ('=')
sign. The following extended options are supported:
stride=stride-size
Configure the filesystem for a RAID array with
stride-size filesystem blocks. This is the number of
blocks read or written to disk before moving to next
disk. This mostly affects placement of filesystem
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.
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.
test_fs
Set a flag in the filesystem superblock indicating
that it may be mounted using experimental 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 removing 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.
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 interval-between-checks as
days, m as months, and w as weeks. A value of zero will disable
the time-dependent 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
resulting in data loss or corruption.
-j Add an ext3 journal to the filesystem. If the -J option is not
specified, the default journal parameters will be used to create
an appropriately sized journal (given the size of the
filesystem) stored within the filesystem. Note that you must be
using 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
filesystem, an immutable file, .journal, will be created in the
top-level directory of the filesystem, as it is the only safe
way to create the journal inode while the filesystem is mounted.
While the ext3 journal is visible, it is not safe to delete it,
or modify it while the filesystem is mounted; for this reason
the file is marked immutable. While checking unmounted
filesystems, e2fsck(8) will automatically move .journal files to
the invisible, reserved journal inode. For all filesystems
except for the root filesystem, this should happen
automatically 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 automatically 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 external 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 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
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 fragmentation, 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
Set the last-mounted directory for the filesystem.
-o [^]mount-option[,...]
Set or clear the indicated default mount options in the
filesystem. 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 filesystem's superblock;
mount options without 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.
bsdgroups
Emulate BSD behaviour when creating new files: they
will take the group-id of the directory in which
they were created. The standard System V behaviour
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.
-O [^]feature[,...]
Set or clear the indicated filesystem features (options) in the
filesystem. More than one filesystem feature can be cleared or
set by separating features with commas. Filesystem features
prefixed with a caret character ('^') will be cleared in the
filesystem's superblock; filesystem features without a prefix
character or prefixed with a plus character ('+') will be added
to the filesystem.
The following filesystem features can be set or cleared using
tune2fs:
dir_index
Use hashed b-trees to speed up lookups in large
directories.
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 bitmaps, as mke2fs(8) will do when it
creates a freshly formated 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.
large_file
Filesystem can contain files that are greater than
2GB. (Modern kernels set this feature automatically
when a file > 2GB is created.)
resize_inode
Reserve space so the block group descriptor table
may grow in the future. Tune2fs only supports
clearing this filesystem 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 and keep a high watermark 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.
-r reserved-blocks-count
Set the number of reserved filesystem blocks.
-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 consistent 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 <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 manual page was written by Christian Kuhtz
<chk@data-hh.Hanse.DE>. Time-dependent checking was added by Uwe Ohse
<uwe@tirka.gun.de>.
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)