.\" -*- nroff -*-
.TH FSTRIM 8 "November 2010" "util-linux" "System Administration"
.SH NAME
fstrim \- discard unused blocks on a mounted filesystem
.SH SYNOPSIS
.B fstrim
.RB [ \-o
.IR offset ]
.RB [ \-l
.IR length ]
.RB [ \-m
.IR minimum-free-extent ]
.RB [ \-v ]
.I mountpoint
.SH DESCRIPTION
.B fstrim
is used on a mounted filesystem to discard (or "trim") blocks which are not in
use by the filesystem. This is useful for solid-state drives (SSDs) and
thinly-provisioned storage.
.PP
By default,
.B fstrim
will discard all unused blocks in the filesystem. Options may be used to
modify this behavior based on range or size, as explained below.
.PP
The
.I mountpoint
argument is the pathname of the directory where the filesystem
is mounted.
.SH OPTIONS
The \fIoffset\fR, \fIlength\fR, and \fIminimum-free-extent\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\-h, \-\-help\fP"
Display help text and exit.
.IP "\fB\-o, \-\-offset\fP \fIoffset\fP"
Byte offset in filesystem from which to begin searching for free blocks
to discard. Default value is zero, starting at the beginning of the
filesystem.
.IP "\fB\-l, \-\-length\fP \fIlength\fP"
Number of bytes after starting point to search for free blocks to discard.
If the specified value extends past the end of the filesystem,
.B fstrim
will stop at the filesystem size boundary. Default value extends to the end
of the filesystem.
.IP "\fB\-m, \-\-minimum\fP \fIminimum-free-extent\fP"
Minimum contiguous free range to discard, in bytes. (This value is internally
rounded up to a multiple of the filesystem block size). Free ranges smaller
than this will be ignored. By increasing this value, the fstrim operation
will complete more quickly for filesystems with badly fragmented freespace,
although not all blocks will be discarded. Default value is zero, discard
every free block.
.IP "\fB\-v, \-\-verbose\fP"
Verbose execution. When specified
.B fstrim
will output the number of bytes passed from the filesystem
down the block stack to the device for potential discard. This number is a
maximum discard amount from the storage device's perspective, because
.I FITRIM
ioctl called repeated will keep sending the same sectors for discard repeatedly.
.B fstrim
will report the same potential discard bytes each time, but only sectors which
had been written to between the discards would actually be discarded by the
storage device. Further, the kernel block layer reserves the right to adjust
the discard ranges to fit raid stripe geometry, non-trim capable devices in a
LVM setup, etc. These reductions would not be reflected in fstrim_range.len
(the
.B --length
option).
.SH AUTHOR
.nf
Lukas Czerner <lczerner@redhat.com>
Karel Zak <kzak@redhat.com>
.fi
.SH SEE ALSO
.BR mount (8)
.SH AVAILABILITY
The fstrim command is part of the util-linux package and is available from
ftp://ftp.kernel.org/pub/linux/utils/util-linux/.
