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TUNE2FS(8) TUNE2FS(8)
NAME
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 param-
eters on Linux ext2/ext3 filesystems.
OPTIONS
-c max-mount-counts
Adjust the maximal mounts count between two filesystem checks. 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 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.
-C mount-count
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.
-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) check-
ing 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 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 sep-
arated, and may take an argument using the equals (’=’) sign. The follow-
ing 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.
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.
-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 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 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 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 fea-
tures 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.
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 con-
sistent state. Tune2fs will print a message requesting that the system
administrator run e2fsck(8) if necessary. After setting the dir_index fea-
ture, 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 sup-
port 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 fea-
ture in order to have a valid filesystem.
-T time-last-checked
Set the time the filesystem was last checked using e2fsck. This can be use-
ful in scripts which use a Logical Volume Manager to make a consistent snap-
shot 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-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 AT linux.org>. It is currently being
maintained by Theodore Ts’o <tytso AT alum.edu>. tune2fs uses the ext2fs library
written by Theodore Ts’o <tytso AT mit.edu>. This manual page was written by Chris-
tian Kuhtz <chk AT data-hh.DE>. Time-dependent checking was added by Uwe Ohse
<uwe AT tirka.de>.
AVAILABILITY
tune2fs is part of the e2fsprogs package and is available from
http://e2fsprogs.sourceforge.net.
SEE ALSO
dumpe2fs(8), e2fsck(8), mke2fs(8)
E2fsprogs version 1.38 June 2005 TUNE2FS(8)
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On Apache/1.3.41 (Unix) PHP/5.2.5 mod_perl/1.30 mod_gzip/1.3.26.1a
Under GNU General Public License
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