.\" -*- nroff -*-
.TH FALLOCATE 1 "July 2009" "util-linux" "User Commands"
.SH NAME
fallocate \- preallocate space to a file
.SH SYNOPSIS
.B fallocate
.RB [ \-n ]
.RB [ \-o
.IR offset ]
.B \-l
.IR length
.I filename
.SH DESCRIPTION
.B 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.
.PP
As of the Linux Kernel v2.6.31, the fallocate system call is supported by the
btrfs, ext4, ocfs2, and xfs filesystems.
.PP
The exit code returned by
.B fallocate
is 0 on success and 1 on failure.
.PP
.SH OPTIONS
The \fIlength\fR and \fIoffset\fR arguments may be followed by binary (2^N)
suffixes KiB, MiB, GiB, TiB, PiB and EiB (the "iB" is optional, e.g. "K" has the
same meaning as "KiB") or decimal (10^N) suffixes KB, MB, GB, PB and EB.
.IP "\fB\-h, \-\-help\fP"
Print help and exit.
.IP "\fB\-n, \-\-keep-size\fP"
Do not modify the apparent length of the file. This may effectively allocate
blocks past EOF, which can be removed with a truncate.
.IP "\fB\-o, \-\-offset\fP \fIoffset\fP
Specifies the beginning offset of the allocation, in bytes.
.IP "\fB\-l, \-\-length\fP \fIlength\fP
Specifies the length of the allocation, in bytes.
.SH AUTHORS
.nf
Eric Sandeen <sandeen@redhat.com>
Karel Zak <kzak@redhat.com>
.fi
.SH SEE ALSO
.BR fallocate (2),
.BR posix_fallocate (3),
.BR truncate (1)
.SH AVAILABILITY
The fallocate command is part of the util-linux package and is available from
ftp://ftp.kernel.org/pub/linux/utils/util-linux/.