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fstrim [-o offset] [-l length] [-m minimum-free-extent] [-v] mountpoint
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
The mountpoint argument is the pathname of the directory where the
filesystem is mounted.
The offset, length, and minimum-free-extent 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.
Print help 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
The fstrim command is part of the util-linux-ng package and is avail-
able from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.
Nov 2010 FSTRIM(8)