TUNE2FS(8) System Manager's Manual TUNE2FS(8)
tune2fs - adjust tunable filesystem parameters on ext2/ext3 filesystems
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 ] [ -L volume-name ] [ -M last-mounted-directory ] [
-O [^]feature[,...] ] [ -T time-last-checked ] [ -U UUID ] device
tune2fs allows the system administrator to adjust various tunable
filesystem parameters on Linux ext2/ext3 filesystems.
Adjust the maximal mounts count between two filesystem checks.
If max-mount-counts is 0 or -1, the number of times the filesys-
tem 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 filesys-
tem 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.
Set the number of times the filesystem has been mounted. Can be
used in conjunction with -c to force an fsck on the filesystem
at the next reboot.
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
continue Continue normal execution.
remount-ro Remount filesystem read-only.
panic Cause a kernel panic.
-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 jour-
nal (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 corrup-
Set the group which can use 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.
Adjust the maximal time between two filesystem checks. No post-
fix or d result in days, m in months, and w in weeks. A value
of zero will disable the time-dependent checking.
It is strongly recommended that either -c (mount-count-depen-
dent) or -i (time-dependent) checking be enabled to force peri-
odic 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 to go unnoticed until they cause 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 filesys-
tem) stored within the filesystem. Note that you must be using
a kernel which has ext3 support in order to actually make use of
If this option is used to create a journal on a mounted filesys-
tem, 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 invisi-
ble, 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
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:
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.
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
Instead of specifying a device name directly, exter-
nal-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
Only one of the size or device options can be given for a
-l List the contents of the filesystem superblock.
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 warn-
ing. The volume label can be used by mount(8), fsck(8), and
/etc/fstab(5) (and possibly others) by specifying LABEL=vol-
ume_label instead of a block special device name like /dev/hda5.
Set the percentage of reserved filesystem blocks.
Set the last-mounted directory for the filesystem.
Set or clear the indicated default mount options in the filesys-
tem. Default mount options can be overriden by mount options
specified either in /etc/fstab(5) or on the command line argu-
ments to mount(8). Older kernels may not support this feature;
in particular, kernels which predate 2.4.20 will almost cer-
tainly 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 char-
acter ('^') 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.
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 direc-
try 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 directory itself.
Enable user-specified extended attributes.
acl Enable Posix Access Control Lists.
uid16 Disables 32-bit UIDs and GIDs. This is for interop-
erability with older kernels which only store and
expect 16-bit values.
When the filesystem is mounted with journalling
enabled, all data (not just metadata) is committed
into the journal prior to being written into the
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
When the filesystem is mounted with journalling
enabled, data may be written into the main filesys-
tem 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.
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
Use hashed b-trees to speed up lookups in large
Store file type information in directory entries.
Use a journal to ensure filesystem consistency even
across unclean shutdowns. Setting the filesystem
feature is equivalent to using the -j option.
Limit the number of backup superblocks to save space
on large filesystems.
After setting or clearing sparse_super and filetype 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 neces-
sary. After setting the dir_index feature, e2fsck -D can be run
to convert existing directories to the hashed B-tree format.
Warning: Linux kernels before 2.0.39 and many 2.1 series kernels
do not support the filesystems that use any of these features.
Enabling certain filesystem features may prevent the filesystem
from being mounted by kernels which do not support those fea-
Set the number of reserved filesystem blocks.
Turn the sparse super feature off or on. Turning this feature
on saves space on really big filesystems. This is the same as
using the -O sparse_super option.
Warning: Linux kernels before 2.0.39 do not support this fea-
ture. Neither do all Linux 2.1 kernels; please don't use this
unless you know what you're doing! You need to run e2fsck(8) on
the filesystem after changing this feature in order to have a
Set the time the filesystem was last checked using e2fsck. 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 cor-
rupted 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[[HHMM]SS]. The keyword now is also accepted, in
which case the last checked time will be set to the current
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
Set the universally unique identifier (UUID) of the filesystem
to UUID. The format of the UUID is a series of hex digits sepa-
rated 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.
We haven't found any bugs yet. That doesn't mean there aren't any...
tune2fs was written by Remy Card <Remy.CardATlinux.org>. It is cur-
rently being maintained by Theodore Ts'o <tytsoATalum.edu>. tune2fs
uses the ext2fs library written by Theodore Ts'o <tytsoATmit.edu>. This
manual page was written by Christian Kuhtz <chkATdata-hh.DE>.
Time-dependent checking was added by Uwe Ohse <uweATtirka.de>.
tune2fs is part of the e2fsprogs package and is available from
dumpe2fs(8), e2fsck(8), mke2fs(8)
E2fsprogs version 1.37 March 2005 TUNE2FS(8)