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 frequently, or even using mount -o discard, might
negatively affect the lifetime of poor-quality SSD devices. For most
desktop and server systems the sufficient trimming frequency is once
a week. Note that not all devices support a queued trim, so each
trim command incurs a performance penalty on whatever else might be
trying to use the disk at the time.
The offset, length, and minimum-size 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.
-o, --offset offset
Byte offset in the filesystem from which to begin searching
for free blocks to discard. The default value is zero,
starting at the beginning of the filesystem.
-l, --length length
The number of bytes (after the 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. The default value extends to the end of the
-m, --minimum minimum-size
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. With this option 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).
Display version information and exit.
Display help text and exit.
This page is part of the util-linux (a random collection of Linux
utilities) project. Information about the project can be found at
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2015-08-08. If you discover any rendering problems in this HTML ver‐
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util-linux July 2014 FSTRIM(8)