tune2fs - adjust tunable filesystem parameters on second extended filesystems
tune2fs [ -l ] [ -c max-mount-counts ] [ -e errors-behavior ] [ -f ] [ -i interval-
between-checks ] [ -j ] [ -J journal-options ] [ -m reserved-blocks-percentage ] [ -o
[ -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 adjusts tunable filesystem parameters on a Linux second extended filesystem.
Adjust the maximal mounts count between two filesystem checks. If max-mount-counts
is 0 then 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 cor-
rupt 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.
Set the number of times the filesystem has been mounted. Can be used in conjunc-
tion 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 the following:
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 journal (or is corrupted such that it appears to have an external jour-
nal), 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.
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 postfix or d result in
days, m in months, and w in weeks. A value of zero will disable the time-dependent
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 to go unnoticed until they cause data loss or cor-
-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
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
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.
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
Only one of the size or device options can be given for a filesystem.
-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 trun-
cate 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.
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 filesystem. Default mount
options can be overriden by mount options specified either in /etc/fstab(5) or on
the command line arguments to mount(8). Older kernels may not support this fea-
ture; 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 com-
mas. 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.
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 crrent process, unless the directry 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 interoperability 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 main filesystem.
When the filesystem is mounted with journalling enabled, all data is
forced directly out to the main file system prior to its metadata being
commutted to the journal.
When the filesystem is mounted with journalling enabled, data may be
written into the main filesystem after its metadata has been commutted
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 com-
mas. Filesystem features prefixed with a caret character ('^') will be cleared in
the filesystem's superblock; filesystem features without a prefix character or pre-
fixed with a plus character ('+') will be added to the filesystem.
The following filesystem features can be set or cleared using tune2fs:
Limit the number of backup superblocks to save space on large filesys-
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
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)
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
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 feature. 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 valid filesystem.
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 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[[HHMM]SS]. The keyword now is also accepted, in
which case the last checked time will be set to the current time.
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.
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
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.Card@linux.org>. tune2fs uses the ext2fs library
written by Theodore Ts'o <email@example.com>. This manual page was written by Christian Kuhtz
<chk@data-hh.Hanse.DE>. Time-dependent checking was added by Uwe Ohse <firstname.lastname@example.org>.
tune2fs is part of the e2fsprogs package and is available from http://e2fsprogs.source-
dumpe2fs(8), e2fsck(8), mke2fs(8)
E2fsprogs version 1.32 November 2002 TUNE2FS(8)