chattr.1.in: Clarify man page.

[thirdparty/e2fsprogs.git] / misc / tune2fs.8.in

.\" 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 \-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 maximal mounts count between two filesystem checks.  If 
.I max-mount-counts
is 0 then 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.
Can be used in conjunction with -c to force an fsck on
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
.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 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 to go
unnoticed until they cause 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.
.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@.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 reserved filesystem blocks.
.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 overriden 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 directry 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.
.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 commutted 
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 commutted
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 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.
.RE
.IP
After setting or clearing 
.B sparse_super
and 
.B filetype 
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.
.IP
.B 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.
.TP
.BI \-r " reserved-blocks-count"
Set the number of reserved filesystem blocks.
.TP
.BR \-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
.B "\-O sparse_super"
option.
.IP
.B 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
.BR e2fsck (8)
on the filesystem after changing this feature in order to have a valid
filesystem.
.TP
.BI \-T " time-last-checked"
Set the time the filesystem was last checked using
.BR  e2fsck .
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[[HHMM]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 <Remy.Card@linux.org>.  It is currently being
maintained by Theodore Ts'o <tytso@alum.mit.edu>.
.B tune2fs
uses the ext2fs library written by Theodore Ts'o <tytso@mit.edu>.
This manual page was written by Christian Kuhtz <chk@data-hh.Hanse.DE>.
Time-dependent checking was added by Uwe Ohse <uwe@tirka.gun.de>.
.SH AVAILABILITY
.B tune2fs
is part of the e2fsprogs package and is available from 
http://e2fsprogs.sourceforge.net.
.SH SEE ALSO
.BR dumpe2fs (8),
.BR e2fsck (8),
.BR mke2fs (8)