From Linux Man Pages
tune2fs - adjust tunable filesystem parameters on ext2/ext3 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 ] [ -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
filesystems.
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.
-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 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 postfix 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-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 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 natu-
rally 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 argu-
ment 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 exter-
nal 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 jour-
nal 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.
-L volume-label
Set the volume label of the filesystem. Ext2 filesystem labels can be at most 16 characters long; if vol-
ume-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 reserved filesystem blocks.
-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 overrid-
den 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 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 pre-
fixed 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 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 com-
mitted 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 through-
put, 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 fea-
ture 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 char-
acter 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.
has_journal
Use a journal to ensure filesystem consistency even across unclean shutdowns. Setting the
filesystem feature is equivalent to using the -j option.
sparse_super
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 necessary. 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 features.
-r reserved-blocks-count
Set the number of reserved filesystem blocks.
-s [0|1]
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.
-T time-last-checked
Set the time the filesystem was last checked using e2fsck. This can be useful in scripts which use a Log-
ical 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. YYYYM-
MDD[[HHMM]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-gener-
ated UUID.
BUGS
We haven't found any bugs yet. That doesn't mean there aren't any...
AVAILABILITY
tune2fs is part of the e2fsprogs package and is available from http://e2fsprogs.sourceforge.net.
RELATED
dumpe2fs(8), e2fsck(8), mke2fs(8)
CATEGORY