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 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 code 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.
-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 effec‐ tively 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) and tmpfs (since Linux 3.5).
-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 alloca‐ tion 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 preal‐ located 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 modi‐ fication.
Available since Linux 3.14 for ext4 (only for extent-based files) and XFS.
-V, version Display version information and exit.
-h, help Display help text and exit. AUTHORS Eric Sandeen ⟨sandeen@redhat.com⟩ Karel Zak ⟨kzak@redhat.com⟩ SEE ALSO truncate(1), fallocate(2), posixfallocate(3) AVAILABILITY
The fallocate command is part of the util-linux package and is avail‐ able from Linux Kernel Archive ⟨https://www.kernel.org/pub/linux/utils
/util-linux/⟩.
util-linux April 2014 FALLOCATE(1)