fallocate(1) - Linux man page

Name

fallocate - preallocate space to a file.

Synopsis

fallocate [-n] [-o offset] -l length filename

Description

fallocate is used to preallocate blocks to a file. For filesystems which support the fallocate system call, this 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 zeros.

As of the Linux Kernel v2.6.31, the fallocate system call is supported by the btrfs, ext4, ocfs2, and xfs filesystems.

The exit code returned by fallocate is 0 on success and 1 on failure.

Options

-h, --help
Print help and exit.
-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 allocation, in bytes. Suffixes of k, m, g, t, p, e may be specified to denote KiB, MiB, GiB, etc.
-l, --length length
Specifies the length of the allocation, in bytes. Suffixes of k, m, g, t, p, e may be specified to denote KiB, MiB, GiB, etc.

Authors

Eric Sandeen <sandeen@redhat.com>
Karel Zak <kzak@redhat.com>

See Also

fallocate(2), posix_fallocate(3), truncate(1)

Availability

The fallocate command is part of the util-linux-ng package and is available from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.

Referenced By

virt-resize(1), virt-sparsify(1)