util-linux (2.39)
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VersionsFALLOCATE(1) User Commands FALLOCATE(1)
NAME
fallocate - preallocate or deallocate space to a file
SYNOPSIS
fallocate [-c|-p|-z] [-o offset] -l length [-n] filename
fallocate -d [-o offset] [-l length] filename
fallocate -x [-o offset] -l length filename
DESCRIPTION
fallocate is used to manipulate the allocated disk space for a file, either to deallocate or preallocate it. For
filesystems which support the fallocate(2) system call, preallocation is done quickly by allocating blocks and
marking them as uninitialized, requiring no IO to the data blocks. This is much faster than creating a file by
filling it with zeroes.
The exit status returned by fallocate is 0 on success and 1 on failure.
OPTIONS
The length and offset arguments may be followed by the multiplicative suffixes KiB (=1024), MiB (=1024*1024), and
so on for GiB, TiB, PiB, EiB, ZiB, and YiB (the "iB" is optional, e.g., "K" has the same meaning as "KiB") or the
suffixes KB (=1000), MB (=1000*1000), and so on for GB, TB, PB, EB, ZB, and YB.
The options --collapse-range, --dig-holes, --punch-hole, and --zero-range are mutually exclusive.
-c, --collapse-range
Removes a byte range from a file, without leaving a hole. The byte range to be collapsed starts at offset and
continues for length bytes. At the completion of the operation, the contents of the file starting at the
location offset+length will be appended at the location offset, and the file will be length bytes smaller.
The option --keep-size may not be specified for the collapse-range operation.
Available since Linux 3.15 for ext4 (only for extent-based files) and XFS.
A filesystem may place limitations on the granularity of the operation, in order to ensure efficient
implementation. Typically, offset and length must be a multiple of the filesystem logical block size, which
varies according to the filesystem type and configuration. If a filesystem has such a requirement, the
operation will fail with the error EINVAL if this requirement is violated.
-d, --dig-holes
Detect and dig holes. This makes the file sparse in-place, without using extra disk space. The minimum size
of the hole depends on filesystem I/O block size (usually 4096 bytes). Also, when using this option,
--keep-size is implied. If no range is specified by --offset and --length, then the entire file is analyzed
for holes.
You can think of this option as doing a "cp --sparse" and then renaming the destination file to the original,
without the need for extra disk space.
See --punch-hole for a list of supported filesystems.
-i, --insert-range
Insert a hole of length bytes from offset, shifting existing data.
-l, --length length
Specifies the length of the range, in bytes.
-n, --keep-size
Do not modify the apparent length of the file. This may effectively allocate blocks past EOF, which can be
removed with a truncate.
-o, --offset offset
Specifies the beginning offset of the range, in bytes.
-p, --punch-hole
Deallocates space (i.e., creates a hole) in the byte range starting at offset and continuing for length
bytes. Within the specified range, partial filesystem blocks are zeroed, and whole filesystem blocks are
removed from the file. After a successful call, subsequent reads from this range will return zeroes. This
option may not be specified at the same time as the --zero-range option. Also, when using this option,
--keep-size is implied.
Supported for XFS (since Linux 2.6.38), ext4 (since Linux 3.0), Btrfs (since Linux 3.7), tmpfs (since Linux
3.5) and gfs2 (since Linux 4.16).
-v, --verbose
Enable verbose mode.
-x, --posix
Enable POSIX operation mode. In that mode allocation operation always completes, but it may take longer time
when fast allocation is not supported by the underlying filesystem.
-z, --zero-range
Zeroes space in the byte range starting at offset and continuing for length bytes. Within the specified
range, blocks are preallocated for the regions that span the holes in the file. After a successful call,
subsequent reads from this range will return zeroes.
Zeroing is done within the filesystem preferably by converting the range into unwritten extents. This
approach means that the specified range will not be physically zeroed out on the device (except for partial
blocks at the either end of the range), and I/O is (otherwise) required only to update metadata.
Option --keep-size can be specified to prevent file length modification.
Available since Linux 3.14 for ext4 (only for extent-based files) and XFS.
-h, --help
Display help text and exit.
-V, --version
Print version and exit.
AUTHORS
[34mEric Sandeen <sandeen@redhat.com>, [34mKarel Zak <kzak@redhat.com>
SEE ALSO
truncate(1), fallocate(2), posix_fallocate(3)
REPORTING BUGS
For bug reports, use the issue tracker at [34mhttps://github.com/util-linux/util-linux/issues.
AVAILABILITY
The fallocate command is part of the util-linux package which can be downloaded from [34mLinux Kernel Archive
<https://www.kernel.org/pub/linux/utils/util-linux/>.
util-linux 2.39 2022-05-11 FALLOCATE(1)
NAME
fallocate - preallocate or deallocate space to a file
SYNOPSIS
fallocate [-c|-p|-z] [-o offset] -l length [-n] filename
fallocate -d [-o offset] [-l length] filename
fallocate -x [-o offset] -l length filename
DESCRIPTION
fallocate is used to manipulate the allocated disk space for a file, either to deallocate or preallocate it. For
filesystems which support the fallocate(2) system call, preallocation is done quickly by allocating blocks and
marking them as uninitialized, requiring no IO to the data blocks. This is much faster than creating a file by
filling it with zeroes.
The exit status returned by fallocate is 0 on success and 1 on failure.
OPTIONS
The length and offset arguments may be followed by the multiplicative suffixes KiB (=1024), MiB (=1024*1024), and
so on for GiB, TiB, PiB, EiB, ZiB, and YiB (the "iB" is optional, e.g., "K" has the same meaning as "KiB") or the
suffixes KB (=1000), MB (=1000*1000), and so on for GB, TB, PB, EB, ZB, and YB.
The options --collapse-range, --dig-holes, --punch-hole, and --zero-range are mutually exclusive.
-c, --collapse-range
Removes a byte range from a file, without leaving a hole. The byte range to be collapsed starts at offset and
continues for length bytes. At the completion of the operation, the contents of the file starting at the
location offset+length will be appended at the location offset, and the file will be length bytes smaller.
The option --keep-size may not be specified for the collapse-range operation.
Available since Linux 3.15 for ext4 (only for extent-based files) and XFS.
A filesystem may place limitations on the granularity of the operation, in order to ensure efficient
implementation. Typically, offset and length must be a multiple of the filesystem logical block size, which
varies according to the filesystem type and configuration. If a filesystem has such a requirement, the
operation will fail with the error EINVAL if this requirement is violated.
-d, --dig-holes
Detect and dig holes. This makes the file sparse in-place, without using extra disk space. The minimum size
of the hole depends on filesystem I/O block size (usually 4096 bytes). Also, when using this option,
--keep-size is implied. If no range is specified by --offset and --length, then the entire file is analyzed
for holes.
You can think of this option as doing a "cp --sparse" and then renaming the destination file to the original,
without the need for extra disk space.
See --punch-hole for a list of supported filesystems.
-i, --insert-range
Insert a hole of length bytes from offset, shifting existing data.
-l, --length length
Specifies the length of the range, in bytes.
-n, --keep-size
Do not modify the apparent length of the file. This may effectively allocate blocks past EOF, which can be
removed with a truncate.
-o, --offset offset
Specifies the beginning offset of the range, in bytes.
-p, --punch-hole
Deallocates space (i.e., creates a hole) in the byte range starting at offset and continuing for length
bytes. Within the specified range, partial filesystem blocks are zeroed, and whole filesystem blocks are
removed from the file. After a successful call, subsequent reads from this range will return zeroes. This
option may not be specified at the same time as the --zero-range option. Also, when using this option,
--keep-size is implied.
Supported for XFS (since Linux 2.6.38), ext4 (since Linux 3.0), Btrfs (since Linux 3.7), tmpfs (since Linux
3.5) and gfs2 (since Linux 4.16).
-v, --verbose
Enable verbose mode.
-x, --posix
Enable POSIX operation mode. In that mode allocation operation always completes, but it may take longer time
when fast allocation is not supported by the underlying filesystem.
-z, --zero-range
Zeroes space in the byte range starting at offset and continuing for length bytes. Within the specified
range, blocks are preallocated for the regions that span the holes in the file. After a successful call,
subsequent reads from this range will return zeroes.
Zeroing is done within the filesystem preferably by converting the range into unwritten extents. This
approach means that the specified range will not be physically zeroed out on the device (except for partial
blocks at the either end of the range), and I/O is (otherwise) required only to update metadata.
Option --keep-size can be specified to prevent file length modification.
Available since Linux 3.14 for ext4 (only for extent-based files) and XFS.
-h, --help
Display help text and exit.
-V, --version
Print version and exit.
AUTHORS
[34mEric Sandeen <sandeen@redhat.com>, [34mKarel Zak <kzak@redhat.com>
SEE ALSO
truncate(1), fallocate(2), posix_fallocate(3)
REPORTING BUGS
For bug reports, use the issue tracker at [34mhttps://github.com/util-linux/util-linux/issues.
AVAILABILITY
The fallocate command is part of the util-linux package which can be downloaded from [34mLinux Kernel Archive
<https://www.kernel.org/pub/linux/utils/util-linux/>.
util-linux 2.39 2022-05-11 FALLOCATE(1)