.\" -*- nroff -*-
.TH FALLOCATE 1 "September 2011" "util-linux" "User Commands"
.SH NAME
fallocate \- preallocate or deallocate space to a file
.SH SYNOPSIS
.B fallocate
.RB [ \-n ]
.RB [ \-p ]
.RB [ \-o
.IR offset ]
.B \-l
.IR length
.I filename
.PP
.B fallocate
.RB \-d
.RB [ \-o
.IR offset ]
.RB [ \-l
.IR length ]
.I filename
.SH DESCRIPTION
.B 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 zeros.
.PP
As of the Linux Kernel v2.6.31, the fallocate system call is supported by the
btrfs, ext4, ocfs2, and xfs filesystems. Support for options needed to run with
\fI\-\-punch-hole\fR or \fI\-\-detect-holes\fR was added in Linux 2.6.38.
.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 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.
.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\-p, \-\-punch-hole\fP"
Punch holes in the file, the range should not exceed the length of the file.
.IP "\fB\-d, \-\-dig-holes\fP"
Detect and dig holes. Makes the file sparse in-place, without using extra disk
space. The minimal size of the hole depends on filesystem I/O block size
(usually 4096 bytes). Also, when using this option, \fI\-\-keep-size\fP is
implied.
.PP
.IP
You can think of this as doing a "\fBcp --sparse\fP" and
renaming the dest file as the original, without the need for extra disk space.
.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.
.IP "\fB\-h, \-\-help\fP"
Display help text and exit.
.IP "\fB-v, \-\-verbose"
Enable verbose mode.
.IP "\fB-V, \-\-version"
Display version information and exit.
.SH AUTHORS
.UR sandeen@redhat.com
Eric Sandeen
.UE
.br
.UR kzak@redhat.com
Karel Zak
.UE
.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
.UR ftp://\:ftp.kernel.org\:/pub\:/linux\:/utils\:/util-linux/
Linux Kernel Archive
.UE .
