.\" Revision 1.0 93/06/3 23:00 chk .\" Initial revision .\" .\" .TH TUNE2FS 8 "@E2FSPROGS_MONTH@ @E2FSPROGS_YEAR@" "E2fsprogs version @E2FSPROGS_VERSION@" .SH NAME tune2fs \- adjust tunable filesystem parameters on ext2/ext3 filesystems .SH SYNOPSIS .B tune2fs [ .B \-l ] [ .B \-c .I max-mount-counts ] [ .B \-e .I errors-behavior ] [ .B \-f ] [ .B \-i .I interval-between-checks ] [ .B \-j ] [ .B \-J .I journal-options ] [ .B \-m .I reserved-blocks-percentage ] [ .B \-o .RI [^]mount-options [,...] ] [ .B \-r .I reserved-blocks-count ] [ .B \-s .I sparse-super-flag ] [ .B \-u .I user ] [ .B \-g .I group ] [ .B \-C .I mount-count ] [ .B \-E .I extended-options ] [ .B \-L .I volume-name ] [ .B \-M .I last-mounted-directory ] [ .B \-O .RI [^] feature [,...] ] [ .B \-T .I time-last-checked ] [ .B \-U .I UUID ] device .SH DESCRIPTION .BI tune2fs allows the system administrator to adjust various tunable filesystem parameters on Linux ext2/ext3 filesystems. .SH OPTIONS .TP .BI \-c " max-mount-counts" Adjust the number of mounts after which the filesystem will be checked by .BR e2fsck (8). If .I max-mount-counts is 0 or \-1, the number of times the filesystem is mounted will be disregarded by .BR e2fsck (8) and the kernel. .sp Staggering the mount-counts at which filesystems are forcibly checked will avoid all filesystems being checked at one time when using journaled filesystems. .sp 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 .B 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. .sp See also the .B \-i option for time-dependent checking. .TP .BI \-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 .B \-c option, .BR e2fsck (8) will check the filesystem at the next reboot. .TP .BI \-e " error-behavior" Change the behavior of the kernel code when errors are detected. In all cases, a filesystem error will cause .BR e2fsck (8) to check the filesystem on the next boot. .I error-behavior can be one of the following: .RS 1.2i .TP 1.2i .B continue Continue normal execution. .TP .B remount-ro Remount filesystem read-only. .TP .B panic Cause a kernel panic. .RE .TP .BI \-E " extended-options" 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: .RS 1.2i .TP .BI stride= stride-size Configure the filesystem for a RAID array with .I stride-size filesystem blocks. This is the number of blocks read or written to disk before moving to next disk. This mostly affects placement of filesystem metadata like bitmaps at .BR mke2fs (2) time to avoid placing them on a single disk, which can hurt the performanace. It may also be used by block allocator. .TP .BI stripe-width= stripe-width Configure the filesystem for a RAID array with .I stripe-width filesystem blocks per stripe. This is typically be stride-size * N, where N is the number of data disks in the RAID (e.g. RAID 5 N+1, RAID 6 N+2). This allows the block allocator to prevent read-modify-write of the parity in a RAID stripe if possible when the data is written. .TP .B test_fs Set a flag in the filesystem superblock indicating that it may be mounted using experimental kernel code, such as the ext4dev filesystem. .TP .B ^test_fs Clear the test_fs flag, indicating the filesystem should only be mounted using production-level filesystem code. .RE .TP .B \-f Force the tune2fs operation to complete even in the face of errors. This option is useful when removing the .B 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. .sp .B 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. .TP .BI \-g " group" Set the group which can use the reserved filesystem blocks. The .I 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. .TP .B \-i " \fIinterval-between-checks\fR[\fBd\fR|\fBm\fR|\fBw\fR]" Adjust the maximal time between two filesystem checks. No postfix or .B d result in days, .B m in months, and .B w in weeks. A value of zero will disable the time-dependent checking. .sp It is strongly recommended that either .B \-c (mount-count-dependent) or .B \-i (time-dependent) checking be enabled to force periodic full .BR e2fsck (8) checking of the filesystem. Failure to do so may lead to filesystem corruption (due to bad disks, cables, memory, or kernel bugs) going unnoticed, ultimately resulting in data loss or corruption. .TP .B \-j Add an ext3 journal to the filesystem. If the .B \-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. .IP If this option is used to create a journal on a mounted filesystem, an immutable file, .BR .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, .BR e2fsck (8) will automatically move .B .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, .BR e2fsck (8) must be run from a rescue floppy in order to effect this transition. .IP 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 .BR /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. .TP .BR \-J " journal-options" 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: .RS 1.2i .TP .BI size= journal-size Create a journal stored in the filesystem of size .I 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. @JDEV@.TP @JDEV@.BI device= external-journal @JDEV@Attach the filesystem to the journal block device located on @JDEV@.IR external-journal . @JDEV@The external @JDEV@journal must have been already created using the command @JDEV@.IP @JDEV@.B mke2fs -O journal_dev @JDEV@.I external-journal @JDEV@.IP @JDEV@Note that @JDEV@.I external-journal @JDEV@must be formatted with the same block @JDEV@size as filesystems which will be using it. @JDEV@In addition, while there is support for attaching @JDEV@multiple filesystems to a single external journal, @JDEV@the Linux kernel and @JDEV@.BR e2fsck (8) @JDEV@do not currently support shared external journals yet. @JDEV@.IP @JDEV@Instead of specifying a device name directly, @JDEV@.I external-journal @JDEV@can also be specified by either @JDEV@.BI LABEL= label @JDEV@or @JDEV@.BI UUID= UUID @JDEV@to locate the external journal by either the volume label or UUID @JDEV@stored in the ext2 superblock at the start of the journal. Use @JDEV@.BR dumpe2fs (8) @JDEV@to display a journal device's volume label and UUID. See also the @JDEV@.B -L @JDEV@option of @JDEV@.BR tune2fs (8). .RE @JDEV@.IP @JDEV@Only one of the @JDEV@.BR size " or " device @JDEV@options can be given for a filesystem. .TP .B \-l List the contents of the filesystem superblock. .TP .BI \-L " volume-label" Set the volume label of the filesystem. Ext2 filesystem labels can be at most 16 characters long; if .I volume-label is longer than 16 characters, .B tune2fs will truncate it and print a warning. The volume label can be used by .BR mount (8), .BR fsck (8), and .BR /etc/fstab (5) (and possibly others) by specifying .BI LABEL= volume_label instead of a block special device name like .BR /dev/hda5 . .TP .BI \-m " reserved-blocks-percentage" 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 .BR 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%. .TP .BI \-M " last-mounted-directory" Set the last-mounted directory for the filesystem. .TP .BR \-o " [^]\fImount-option\fR[,...]" Set or clear the indicated default mount options in the filesystem. Default mount options can be overridden by mount options specified either in .BR /etc/fstab (5) or on the command line arguments to .BR 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. .IP 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. .IP The following mount options can be set or cleared using .BR tune2fs : .RS 1.2i .TP .B debug Enable debugging code for this filesystem. .TP .B 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 a directory itself. .TP .B user_xattr Enable user-specified extended attributes. .TP .B acl Enable Posix Access Control Lists. .TP .B uid16 Disables 32-bit UIDs and GIDs. This is for interoperability with older kernels which only store and expect 16-bit values. .TP .B 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. .TP .B 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. .TP .B 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. .RE .TP .BR \-O " [^]\fIfeature\fR[,...]" 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. .IP The following filesystem features can be set or cleared using .BR tune2fs : .RS 1.2i .TP .B large_file Filesystem can contain files that are greater than 2GB. (Modern kernels set this feature automatically when a file > 2GB is created.) .TP .B dir_index Use hashed b-trees to speed up lookups in large directories. .TP .B filetype Store file type information in directory entries. .TP .B has_journal Use a journal to ensure filesystem consistency even across unclean shutdowns. Setting the filesystem feature is equivalent to using the .B \-j option. .TP .B sparse_super Limit the number of backup superblocks to save space on large filesystems. .TP .B resize_inode Reserve space so the block group descriptor table may grow in the future. .B Tune2fs only supports clearing this filesystem feature. .TP .B uninit_groups Allow the kernel to initialize bitmaps and inode tables and keep a high watermark for the unused inodes in a filesystem, to reduce .BR e2fsck (8) time. .RE .IP After setting or clearing .BR sparse_super , .BR uninit_groups , .BR filetype , or .B resize_inode filesystem features, .BR e2fsck (8) must be run on the filesystem to return the filesystem to a consistent state. .B Tune2fs will print a message requesting that the system administrator run .BR e2fsck (8) if necessary. After setting the .B dir_index feature, .B e2fsck -D can be run to convert existing directories to the hashed B-tree format. .TP .BI \-r " reserved-blocks-count" Set the number of reserved filesystem blocks. .TP .BI \-T " time-last-checked" Set the time the filesystem was last checked using .BR 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 .I time-last-checked is the international date format, with an optional time specifier, i.e. YYYYMMDD[HH[MM[SS]]]. The keyword .B now is also accepted, in which case the last checked time will be set to the current time. .TP .BI \-u " user" Set the user who can use the reserved filesystem blocks. .I 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. .TP .BI \-U " UUID" Set the universally unique identifier (UUID) of the filesystem to .IR UUID . The format of the UUID is a series of hex digits separated by hyphens, like this: "c1b9d5a2-f162-11cf-9ece-0020afc76f16". The .I UUID parameter may also be one of the following: .RS 1.2i .TP .I clear clear the filesystem UUID .TP .I random generate a new randomly-generated UUID .TP .I time generate a new time-based UUID .RE .IP The UUID may be used by .BR mount (8), .BR fsck (8), and .BR /etc/fstab (5) (and possibly others) by specifying .BI UUID= uuid instead of a block special device name like .BR /dev/hda1 . .IP See .BR uuidgen (8) for more information. If the system does not have a good random number generator such as .I /dev/random or .IR /dev/urandom , .B tune2fs will automatically use a time-based UUID instead of a randomly-generated UUID. .SH BUGS We haven't found any bugs yet. That doesn't mean there aren't any... .SH AUTHOR .B tune2fs was written by Remy Card . It is currently being maintained by Theodore Ts'o . .B tune2fs uses the ext2fs library written by Theodore Ts'o . This manual page was written by Christian Kuhtz . Time-dependent checking was added by Uwe Ohse . .SH AVAILABILITY .B tune2fs is part of the e2fsprogs package and is available from http://e2fsprogs.sourceforge.net. .SH SEE ALSO .BR debugfs (8), .BR dumpe2fs (8), .BR e2fsck (8), .BR mke2fs (8)