Options may be specified either on the command line or in a
configuration file. Not all command line options can be
specified in configuration files; only the command line options
followed by a [section] label can be used in a configuration
file.
Options that can be used in configuration files are grouped into
related sections containing multiple options. The command line
options and configuration files use the same option sections and
grouping. Configuration file section names are listed in the
command line option sections below. Option names and values are
the same for both command line and configuration file
specification.
Options specified are the combined set of command line parameters
and configuration file parameters. Duplicated options will
result in a respecification error, regardless of the location
they were specified at.
-c configuration_file_option
This option specifies the files that mkfs configuration
will be obtained from. The valid
configuration_file_option is:
options=name
The configuration options will be sourced from
the file specified by the name option string.
This option can be use either an absolute or
relative path to the configuration file to be
read.
-b block_size_options
Section Name: [block]
This option specifies the fundamental block size of the
filesystem. The valid block_size_option is:
size=value
The filesystem block size is specified with a
value in bytes. The default value is 4096
bytes (4 KiB), the minimum is 512, and the
maximum is 65536 (64 KiB).
Although mkfs.xfs will accept any of these
values and create a valid filesystem, XFS on
Linux can only mount filesystems with pagesize
or smaller blocks.
-m global_metadata_options
Section Name: [metadata]
These options specify metadata format options that either
apply to the entire filesystem or aren't easily
characterised by a specific functionality group. The valid
global_metadata_options are:
bigtime=value
This option enables filesystems that can
handle inode timestamps from December 1901 to
July 2486, and quota timer expirations from
January 1970 to July 2486. The value is
either 0 to disable the feature, or 1 to
enable large timestamps.
If this feature is not enabled, the filesystem
can only handle timestamps from December 1901
to January 2038, and quota timers from January
1970 to February 2106.
By default, mkfs.xfs will not enable this
feature. If the option -m crc=0 is used, the
large timestamp feature is not supported and
is disabled.
crc=value
This is used to create a filesystem which
maintains and checks CRC information in all
metadata objects on disk. The value is either
0 to disable the feature, or 1 to enable the
use of CRCs.
CRCs enable enhanced error detection due to
hardware issues, whilst the format changes
also improves crash recovery algorithms and
the ability of various tools to validate and
repair metadata corruptions when they are
found. The CRC algorithm used is CRC32c, so
the overhead is dependent on CPU architecture
as some CPUs have hardware acceleration of
this algorithm. Typically the overhead of
calculating and checking the CRCs is not
noticeable in normal operation.
By default, mkfs.xfs will enable metadata
CRCs.
Formatting a filesystem without CRCs selects
the V4 format, which is deprecated and will be
removed from upstream in September 2030.
Distributors may choose to withdraw support
for the V4 format earlier than this date.
Several other options, noted below, are only
tunable on V4 formats, and will be removed
along with the V4 format itself.
finobt=value
This option enables the use of a separate free
inode btree index in each allocation group.
The value is either 0 to disable the feature,
or 1 to create a free inode btree in each
allocation group.
The free inode btree mirrors the existing
allocated inode btree index which indexes both
used and free inodes. The free inode btree
does not index used inodes, allowing faster,
more consistent inode allocation performance
as filesystems age.
By default, mkfs.xfs will create free inode
btrees for filesystems created with the
(default) -m crc=1 option set. When the option
-m crc=0 is used, the free inode btree feature
is not supported and is disabled.
inobtcount=value
This option causes the filesystem to record
the number of blocks used by the inode btree
and the free inode btree. This can be used to
reduce mount times when the free inode btree
is enabled.
By default, mkfs.xfs will not enable this
option. This feature is only available for
filesystems created with the (default) -m
finobt=1 option set. When the option -m
finobt=0 is used, the inode btree counter
feature is not supported and is disabled.
uuid=value
Use the given value as the filesystem UUID for
the newly created filesystem. The default is
to generate a random UUID.
rmapbt=value
This option enables the creation of a reverse-
mapping btree index in each allocation group.
The value is either 0 to disable the feature,
or 1 to create the btree.
The reverse mapping btree maps filesystem
blocks to the owner of the filesystem block.
Most of the mappings will be to an inode
number and an offset, though there will also
be mappings to filesystem metadata. This
secondary metadata can be used to validate the
primary metadata or to pinpoint exactly which
data has been lost when a disk error occurs.
By default, mkfs.xfs will not create reverse
mapping btrees. This feature is only
available for filesystems created with the
(default) -m crc=1 option set. When the option
-m crc=0 is used, the reverse mapping btree
feature is not supported and is disabled.
reflink=value
This option enables the use of a separate
reference count btree index in each allocation
group. The value is either 0 to disable the
feature, or 1 to create a reference count
btree in each allocation group.
The reference count btree enables the sharing
of physical extents between the data forks of
different files, which is commonly known as
"reflink". Unlike traditional Unix
filesystems which assume that every inode and
logical block pair map to a unique physical
block, a reflink-capable XFS filesystem
removes the uniqueness requirement, allowing
up to four billion arbitrary inode/logical
block pairs to map to a physical block. If a
program tries to write to a multiply-
referenced block in a file, the write will be
redirected to a new block, and that file's
logical-to-physical mapping will be changed to
the new block ("copy on write"). This feature
enables the creation of per-file snapshots and
deduplication. It is only available for the
data forks of regular files.
By default, mkfs.xfs will create reference
count btrees and therefore will enable the
reflink feature. This feature is only
available for filesystems created with the
(default) -m crc=1 option set. When the option
-m crc=0 is used, the reference count btree
feature is not supported and reflink is
disabled.
Note: the filesystem DAX mount option ( -o dax
) is incompatible with reflink-enabled XFS
filesystems. To use filesystem DAX with XFS,
specify the -m reflink=0 option to mkfs.xfs to
disable the reflink feature.
-d data_section_options
Section Name: [data]
These options specify the location, size, and other
parameters of the data section of the filesystem. The
valid data_section_options are:
agcount=value
This is used to specify the number of
allocation groups. The data section of the
filesystem is divided into allocation groups
to improve the performance of XFS. More
allocation groups imply that more parallelism
can be achieved when allocating blocks and
inodes. The minimum allocation group size is
16 MiB; the maximum size is just under 1 TiB.
The data section of the filesystem is divided
into value allocation groups (default value is
scaled automatically based on the underlying
device size).
agsize=value
This is an alternative to using the agcount
suboption. The value is the desired size of
the allocation group expressed in bytes
(usually using the m or g suffixes). This
value must be a multiple of the filesystem
block size, and must be at least 16MiB, and no
more than 1TiB, and may be automatically
adjusted to properly align with the stripe
geometry. The agcount and agsize suboptions
are mutually exclusive.
cowextsize=value
Set the copy-on-write extent size hint on all
inodes created by mkfs.xfs. The value must be
provided in units of filesystem blocks. If
the value is zero, the default value
(currently 32 blocks) will be used.
Directories will pass on this hint to newly
created regular files and directories.
name=value
This can be used to specify the name of the
special file containing the filesystem. In
this case, the log section must be specified
as internal (with a size, see the -l option
below) and there can be no real-time section.
file[=value]
This is used to specify that the file given by
the name suboption is a regular file. The
value is either 0 or 1, with 1 signifying that
the file is regular. This suboption is used
only to make a filesystem image. If the value
is omitted then 1 is assumed.
size=value
This is used to specify the size of the data
section. This suboption is required if -d
file[=1] is given. Otherwise, it is only
needed if the filesystem should occupy less
space than the size of the special file.
sunit=value
This is used to specify the stripe unit for a
RAID device or a logical volume. The value has
to be specified in 512-byte block units. Use
the su suboption to specify the stripe unit
size in bytes. This suboption ensures that
data allocations will be stripe unit aligned
when the current end of file is being extended
and the file size is larger than 512KiB. Also
inode allocations and the internal log will be
stripe unit aligned.
su=value
This is an alternative to using sunit. The su
suboption is used to specify the stripe unit
for a RAID device or a striped logical volume.
The value has to be specified in bytes,
(usually using the m or g suffixes). This
value must be a multiple of the filesystem
block size.
swidth=value
This is used to specify the stripe width for a
RAID device or a striped logical volume. The
value has to be specified in 512-byte block
units. Use the sw suboption to specify the
stripe width size in bytes. This suboption is
required if -d sunit has been specified and it
has to be a multiple of the -d sunit
suboption.
sw=value
suboption is an alternative to using swidth.
The sw suboption is used to specify the stripe
width for a RAID device or striped logical
volume. The value is expressed as a multiplier
of the stripe unit, usually the same as the
number of stripe members in the logical volume
configuration, or data disks in a RAID device.
When a filesystem is created on a logical
volume device, mkfs.xfs will automatically
query the logical volume for appropriate sunit
and swidth values.
noalign
This option disables automatic geometry
detection and creates the filesystem without
stripe geometry alignment even if the
underlying storage device provides this
information.
rtinherit=value
If value is set to 1, all inodes created by
mkfs.xfs will be created with the realtime
flag set. The default is 0. Directories will
pass on this flag to newly created regular
files and directories.
projinherit=value
All inodes created by mkfs.xfs will be
assigned the project quota id provided in
value. Directories will pass on the project
id to newly created regular files and
directories.
extszinherit=value
All inodes created by mkfs.xfs will have this
value extent size hint applied. The value
must be provided in units of filesystem
blocks. Directories will pass on this hint to
newly created regular files and directories.
daxinherit=value
If value is set to 1, all inodes created by
mkfs.xfs will be created with the DAX flag
set. The default is 0. Directories will pass
on this flag to newly created regular files
and directories. By default, mkfs.xfs will
not enable DAX mode.
-f Force overwrite when an existing filesystem is detected on
the device. By default, mkfs.xfs will not write to the
device if it suspects that there is a filesystem or
partition table on the device already.
-i inode_options
Section Name: [inode]
This option specifies the inode size of the filesystem,
and other inode allocation parameters. The XFS inode
contains a fixed-size part and a variable-size part. The
variable-size part, whose size is affected by this option,
can contain: directory data, for small directories;
attribute data, for small attribute sets; symbolic link
data, for small symbolic links; the extent list for the
file, for files with a small number of extents; and the
root of a tree describing the location of extents for the
file, for files with a large number of extents.
The valid inode_options are:
size=value | perblock=value
The inode size is specified either as a value
in bytes with size= or as the number fitting
in a filesystem block with perblock=. The
minimum (and default) value is 256 bytes
without crc, 512 bytes with crc enabled. The
maximum value is 2048 (2 KiB) subject to the
restriction that the inode size cannot exceed
one half of the filesystem block size.
XFS uses 64-bit inode numbers internally;
however, the number of significant bits in an
inode number is affected by filesystem
geometry. In practice, filesystem size and
inode size are the predominant factors. The
Linux kernel (on 32 bit hardware platforms)
and most applications cannot currently handle
inode numbers greater than 32 significant
bits, so if no inode size is given on the
command line, mkfs.xfs will attempt to choose
a size such that inode numbers will be < 32
bits. If an inode size is specified, or if a
filesystem is sufficiently large, mkfs.xfs
will warn if this will create inode numbers >
32 significant bits.
maxpct=value
This specifies the maximum percentage of space
in the filesystem that can be allocated to
inodes. The default value is 25% for
filesystems under 1TB, 5% for filesystems
under 50TB and 1% for filesystems over 50TB.
In the default inode allocation mode, inode
blocks are chosen such that inode numbers will
not exceed 32 bits, which restricts the inode
blocks to the lower portion of the filesystem.
The data block allocator will avoid these low
blocks to accommodate the specified maxpct, so
a high value may result in a filesystem with
nothing but inodes in a significant portion of
the lower blocks of the filesystem. (This
restriction is not present when the filesystem
is mounted with the inode64 option on 64-bit
platforms).
Setting the value to 0 means that essentially
all of the filesystem can become inode blocks,
subject to inode32 restrictions.
This value can be modified with xfs_growfs(8).
align[=value]
This is used to specify that inode allocation
is or is not aligned. The value is either 0 or
1, with 1 signifying that inodes are allocated
aligned. If the value is omitted, 1 is
assumed. The default is that inodes are
aligned. Aligned inode access is normally
more efficient than unaligned access;
alignment must be established at the time the
filesystem is created, since inodes are
allocated at that time. This option can be
used to turn off inode alignment when the
filesystem needs to be mountable by a version
of IRIX that does not have the inode alignment
feature (any release of IRIX before 6.2, and
IRIX 6.2 without XFS patches).
This option is only tunable on the deprecated
V4 format.
attr=value
This is used to specify the version of
extended attribute inline allocation policy to
be used. By default, this is 2, which uses an
efficient algorithm for managing the available
inline inode space between attribute and
extent data.
The previous version 1, which has fixed
regions for attribute and extent data, is kept
for backwards compatibility with kernels older
than version 2.6.16.
This option is only tunable on the deprecated
V4 format.
projid32bit[=value]
This is used to enable 32bit quota project
identifiers. The value is either 0 or 1, with
1 signifying that 32bit projid are to be
enabled. If the value is omitted, 1 is
assumed. (This default changed in release
version 3.2.0.)
This option is only tunable on the deprecated
V4 format.
sparse[=value]
Enable sparse inode chunk allocation. The
value is either 0 or 1, with 1 signifying that
sparse allocation is enabled. If the value is
omitted, 1 is assumed. Sparse inode allocation
is disabled by default. This feature is only
available for filesystems formatted with -m
crc=1.
When enabled, sparse inode allocation allows
the filesystem to allocate smaller than the
standard 64-inode chunk when free space is
severely limited. This feature is useful for
filesystems that might fragment free space
over time such that no free extents are large
enough to accommodate a chunk of 64 inodes.
Without this feature enabled, inode
allocations can fail with out of space errors
under severe fragmented free space conditions.
-l log_section_options
Section Name: [log]
These options specify the location, size, and other
parameters of the log section of the filesystem. The valid
log_section_options are:
agnum=value
If the log is internal, allocate it in this
AG.
internal[=value]
This is used to specify that the log section
is a piece of the data section instead of
being another device or logical volume. The
value is either 0 or 1, with 1 signifying that
the log is internal. If the value is omitted,
1 is assumed.
logdev=device
This is used to specify that the log section
should reside on the device separate from the
data section. The internal=1 and logdev
options are mutually exclusive.
size=value
This is used to specify the size of the log
section.
If the log is contained within the data
section and size isn't specified, mkfs.xfs
will try to select a suitable log size
depending on the size of the filesystem. The
actual logsize depends on the filesystem block
size and the directory block size.
Otherwise, the size suboption is only needed
if the log section of the filesystem should
occupy less space than the size of the special
file. The value is specified in bytes or
blocks, with a b suffix meaning multiplication
by the filesystem block size, as described
above. The overriding minimum value for size
is 512 blocks. With some combinations of
filesystem block size, inode size, and
directory block size, the minimum log size is
larger than 512 blocks.
version=value
This specifies the version of the log. The
current default is 2, which allows for larger
log buffer sizes, as well as supporting
stripe-aligned log writes (see the sunit and
su options, below).
The previous version 1, which is limited to
32k log buffers and does not support stripe-
aligned writes, is kept for backwards
compatibility with very old 2.4 kernels.
This option is only tunable on the deprecated
V4 format.
sunit=value
This specifies the alignment to be used for
log writes. The value has to be specified in
512-byte block units. Use the su suboption to
specify the log stripe unit size in bytes.
Log writes will be aligned on this boundary,
and rounded up to this boundary. This gives
major improvements in performance on some
configurations such as software RAID5 when the
sunit is specified as the filesystem block
size. The equivalent byte value must be a
multiple of the filesystem block size. Version
2 logs are automatically selected if the log
sunit suboption is specified.
The su suboption is an alternative to using
sunit.
su=value
This is used to specify the log stripe. The
value has to be specified in bytes, (usually
using the s or b suffixes). This value must be
a multiple of the filesystem block size.
Version 2 logs are automatically selected if
the log su suboption is specified.
lazy-count=value
This changes the method of logging various
persistent counters in the superblock. Under
metadata intensive workloads, these counters
are updated and logged frequently enough that
the superblock updates become a serialization
point in the filesystem. The value can be
either 0 or 1.
With lazy-count=1, the superblock is not
modified or logged on every change of the
persistent counters. Instead, enough
information is kept in other parts of the
filesystem to be able to maintain the
persistent counter values without needed to
keep them in the superblock. This gives
significant improvements in performance on
some configurations. The default value is 1
(on) so you must specify lazy-count=0 if you
want to disable this feature for older kernels
which don't support it.
This option is only tunable on the deprecated
V4 format.
-n naming_options
Section Name: [naming]
These options specify the version and size parameters for
the naming (directory) area of the filesystem. The valid
naming_options are:
size=value
The directory block size is specified with a
value in bytes. The block size must be a
power of 2 and cannot be less than the
filesystem block size. The default size value
for version 2 directories is 4096 bytes (4
KiB), unless the filesystem block size is
larger than 4096, in which case the default
value is the filesystem block size. For
version 1 directories the block size is the
same as the filesystem block size.
version=value
The naming (directory) version value can be
either 2 or 'ci', defaulting to 2 if
unspecified. With version 2 directories, the
directory block size can be any power of 2
size from the filesystem block size up to
65536.
The version=ci option enables ASCII only case-
insensitive filename lookup and version 2
directories. Filenames are case-preserving,
that is, the names are stored in directories
using the case they were created with.
Note: Version 1 directories are not supported.
ftype=value
This feature allows the inode type to be
stored in the directory structure so that the
readdir(3) and getdents(2) do not need to look
up the inode to determine the inode type.
The value is either 0 or 1, with 1 signifying
that filetype information will be stored in
the directory structure. The default value is
1.
When CRCs are enabled (the default), the ftype
functionality is always enabled, and cannot be
turned off.
In other words, this option is only tunable on
the deprecated V4 format.
-p protofile
If the optional -p protofile argument is given, mkfs.xfs
uses protofile as a prototype file and takes its
directions from that file. The blocks and inodes
specifiers in the protofile are provided for backwards
compatibility, but are otherwise unused. The syntax of
the protofile is defined by a number of tokens separated
by spaces or newlines. Note that the line numbers are not
part of the syntax but are meant to help you in the
following discussion of the file contents.
1 /stand/diskboot
2 4872 110
3 d--777 3 1
4 usr d--777 3 1
5 sh ---755 3 1 /bin/sh
6 ken d--755 6 1
7 $
8 b0 b--644 3 1 0 0
9 c0 c--644 3 1 0 0
10 fifo p--644 3 1
11 slink l--644 3 1 /a/symbolic/link
12 : This is a comment line
13 $
14 $
Line 1 is a dummy string. (It was formerly the
bootfilename.) It is present for backward compatibility;
boot blocks are not used on SGI systems.
Note that some string of characters must be present as the
first line of the proto file to cause it to be parsed
correctly; the value of this string is immaterial since it
is ignored.
Line 2 contains two numeric values (formerly the numbers
of blocks and inodes). These are also merely for backward
compatibility: two numeric values must appear at this
point for the proto file to be correctly parsed, but their
values are immaterial since they are ignored.
The lines 3 through 11 specify the files and directories
you want to include in this filesystem. Line 3 defines the
root directory. Other directories and files that you want
in the filesystem are indicated by lines 4 through 6 and
lines 8 through 10. Line 11 contains symbolic link syntax.
Notice the dollar sign ($) syntax on line 7. This syntax
directs the mkfs.xfs command to terminate the branch of
the filesystem it is currently on and then continue from
the directory specified by the next line, in this case
line 8. It must be the last character on a line. The
colon on line 12 introduces a comment; all characters up
until the following newline are ignored. Note that this
means you cannot have a file in a prototype file whose
name contains a colon. The $ on lines 13 and 14 end the
process, since no additional specifications follow.
File specifications provide the following:
* file mode
* user ID
* group ID
* the file's beginning contents
A 6-character string defines the mode for a file. The
first character of this string defines the file type. The
character range for this first character is -bcdpl. A
file may be a regular file, a block special file, a
character special file, directory files, named pipes
(first-in, first out files), and symbolic links. The
second character of the mode string is used to specify
setuserID mode, in which case it is u. If setuserID mode
is not specified, the second character is -. The third
character of the mode string is used to specify the
setgroupID mode, in which case it is g. If setgroupID
mode is not specified, the third character is -. The
remaining characters of the mode string are a three digit
octal number. This octal number defines the owner, group,
and other read, write, and execute permissions for the
file, respectively. For more information on file
permissions, see the chmod(1) command.
Following the mode character string are two decimal number
tokens that specify the user and group IDs of the file's
owner.
In a regular file, the next token specifies the pathname
from which the contents and size of the file are copied.
In a block or character special file, the next token are
two decimal numbers that specify the major and minor
device numbers. When a file is a symbolic link, the next
token specifies the contents of the link.
When the file is a directory, the mkfs.xfs command creates
the entries dot (.) and dot-dot (..) and then reads the
list of names and file specifications in a recursive
manner for all of the entries in the directory. A scan of
the protofile is always terminated with the dollar ( $ )
token.
-q Quiet option. Normally mkfs.xfs prints the parameters of
the filesystem to be constructed; the -q flag suppresses
this.
-r realtime_section_options
Section Name: [realtime]
These options specify the location, size, and other
parameters of the real-time section of the filesystem. The
valid realtime_section_options are:
rtdev=device
This is used to specify the device which
should contain the real-time section of the
filesystem. The suboption value is the name
of a block device.
extsize=value
This is used to specify the size of the blocks
in the real-time section of the filesystem.
This value must be a multiple of the
filesystem block size. The minimum allowed
size is the filesystem block size or 4 KiB
(whichever is larger); the default size is the
stripe width for striped volumes or 64 KiB for
non-striped volumes; the maximum allowed size
is 1 GiB. The real-time extent size should be
carefully chosen to match the parameters of
the physical media used.
size=value
This is used to specify the size of the real-
time section. This suboption is only needed
if the real-time section of the filesystem
should occupy less space than the size of the
partition or logical volume containing the
section.
noalign
This option disables stripe size detection,
enforcing a realtime device with no stripe
geometry.
-s sector_size_options
Section Name: [sector]
This option specifies the fundamental sector size of the
filesystem. The valid sector_size_option is:
size=value
The sector size is specified with a value in
bytes. The default sector_size is 512 bytes.
The minimum value for sector size is 512; the
maximum is 32768 (32 KiB). The sector_size
must be a power of 2 size and cannot be made
larger than the filesystem block size.
-L label
Set the filesystem label. XFS filesystem labels can be at
most 12 characters long; if label is longer than 12
characters, mkfs.xfs will not proceed with creating the
filesystem. Refer to the mount(8) and xfs_admin(8) manual
entries for additional information.
-N Causes the file system parameters to be printed out
without really creating the file system.
-K Do not attempt to discard blocks at mkfs time.
-V Prints the version number and exits.
