E2fsprogs version 1.46-WIP
tune2fs - adjust tunable filesystem parameters on ext2/ext3/ext4 filesystems
tune2fs [ -l ] [ -c max-mount-counts ] [ -e errors-behavior ] [ -f ] [ -i interval-between-checks ] [ -I new_inode_size ] [ -j ] [ -J journal-options ] [ -m reserved-blocks-percentage ] [ -o [^]mount-options[,...] ] [ -r reserved-blocks-count ] [ -u user ] [ -g group ] [ -C mount-count ] [ -E extended-options ] [ -L volume-label ] [ -M last-mounted-directory ] [ -O [^]feature[,...] ] [ -Q quota-options ] [ -T time-last-checked ] [ -U UUID ] [ -z undo_file ] device
tune2fs allows the system administrator to adjust various tunable filesystem parameters on Linux ext2, ext3, or ext4 filesystems. The current values of these options can be displayed by using the -l option to tune2fs(8) program, or by using the dumpe2fs(8) program.
The device specifier can either be a filename (i.e., /dev/sda1), or a LABEL or UUID specifier: "LABEL=volume-label" or "UUID=uuid". (i.e., LABEL=home or UUID=e40486c6-84d5-4f2f-b99c-032281799c9d).
|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.
Mount-count-dependent checking is disabled by default to avoid unanticipated long reboots while e2fsck does its work. However, you may wish to 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.
|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.|
|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:|
|Set extended options for the filesystem. Extended options are comma separated, and may take an argument using the equals (’=’) sign. The following extended options are supported:|
|-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. If the filesystem appears to require journal replay, the -f flag must be specified twice to proceed.
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 the 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 suffix or d will interpret the number interval-between-checks as days, m as months, and w as weeks. A value of zero will disable the time-dependent checking.
There are pros and cons to disabling these periodic checks; see the discussion under the -c (mount-count-dependent check) option for details.
|-I||Change the inode size used by the file system. This requires rewriting the inode table, so it requires that the file system is checked for consistency first using e2fsck(8). This operation can also take a while and the file system can be corrupted and data lost if it is interrupted while in the middle of converting the file system.|
|-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.|
|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:|
|Only one of the size or device options can be given for a filesystem.|
|-l||List the contents of the filesystem superblock, including the current values of the parameters that can be set via this program.|
|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.|
|Set the percentage of the filesystem which may only be allocated by privileged processes. Reserving some number of filesystem blocks for use by privileged processes is done to avoid filesystem fragmentation, and to allow system daemons, such as syslogd(8), to continue to function correctly after non-privileged processes are prevented from writing to the filesystem. Normally, the default percentage of reserved blocks is 5%.|
|Set the last-mounted directory for the filesystem.|
|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:|
|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. For a detailed description of the file system features, please see the man page ext4(5).|
|The following filesystem features can be set or cleared using tune2fs:|
|After setting or clearing sparse_super, uninit_bg, filetype, or resize_inode filesystem features, the file system may require being checked using e2fsck(8) 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. Enabling certain filesystem features may prevent the filesystem from being mounted by kernels which do not support those features. In particular, the uninit_bg and flex_bg features are only supported by the ext4 filesystem.|
|Set the number of reserved filesystem blocks.|
|Sets ’quota’ feature on the superblock and works on the quota files for the given quota type. Quota options could be one or more of the following:|
|Set the time the filesystem was last checked using e2fsck. The time is interpreted using the current (local) timezone. 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[HH[MM[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:|
|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.|
|-z undo_file||Before overwriting a file system block, write the old contents of the block to an undo file. This undo file can be used with e2undo(8) to restore the old contents of the file system should something go wrong. If the empty string is passed as the undo_file argument, the undo file will be written to a file named tune2fs-device.e2undo in the directory specified via the E2FSPROGS_UNDO_DIR environment variable.
WARNING: The undo file cannot be used to recover from a power or system crash.
We haven’t found any bugs yet. That doesn’t mean there aren’t any...
tune2fs is part of the e2fsprogs package and is available from http://e2fsprogs.sourceforge.net.