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.
By default, 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.
The mountpoint argument is the pathname of the directory where the
filesystem is mounted.
Running fstrim more frequently or even using mount -o discard might
affect lifetime of the poor quality SSD devices. The usual sufficient
frequency is once a week for most desktop and server systems. Note
that not all devices support queued trim, so each trim command incur
a performance penalty to whatever else might be trying to use the
disk at the time.
The offset, length, and minimum-free-extent 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.
Trim all mounted filesystems on devices that support the
discard operation. The other supplied options, like --offset,
--length and --minimum, are applied to all these devices.
Errors from filesystems that do not support the discard
operation are silently ignored.
Display help text and exit.
-o, --offset offset
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.
-l, --length length
Number of bytes after starting point to search for free blocks
to discard. If the specified value extends past the end of
the filesystem, fstrim will stop at the filesystem size
boundary. Default value extends to the end of the filesystem.
-m, --minimum minimum-free-extent
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.
Verbose execution. When specified 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 FITRIM ioctl called repeated will keep sending the
same sectors for discard repeatedly.
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 --length option).
This page is part of the util-linux (a random collection of Linux
utilities) project. Information about the project can be found at
⟨https://www.kernel.org/pub/linux/utils/util-linux/⟩. If you have a
bug report for this manual page, send it to
email@example.com. This page was obtained from the
project's upstream Git repository
2014-07-09. If you discover any rendering problems in this HTML ver‐
sion of the page, or you believe there is a better or more up-to-date
source for the page, or you have corrections or improvements to the
information in this COLOPHON (which is not part of the original man‐
ual page), send a mail to firstname.lastname@example.org
util-linux November 2010 FSTRIM(8)