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 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.
remount-ro Remount filesystem read-only.
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.
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.
If this option is used to create a journal on a mounted filesystem, an immutable file, .journal, will be created in the toplevel 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.
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 using it.
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 tune2fs(8) .
Only one of the size or device options can be given for a filesystem.
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.
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.
Enable user-specified extended attributes.
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 committed to the journal.
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.
The following filesystem features can be set or cleared using tune2fs:
Use hashed b-trees to speed up lookups in large directories.
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 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.
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.
clear clear the filesystem UUID
random generate a new randomly-generated 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>. It is currently being maintained by Theodore Ts’o <email@example.com>. tune2fs uses the ext2fs library written by Theodore Ts’o <firstname.lastname@example.org>. This manual page was written by Christian Kuhtz <chk@data-hh.Hanse.DE>. Time-dependent checking was added by Uwe Ohse <email@example.com>.
tune2fs is part of the e2fsprogs package and is available from http://e2fsprogs.sourceforge.net.
dumpe2fs(8) , e2fsck(8) , mke2fs(8)
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