fstrim - discard unused blocks on a mounted filesystem
fstrim [-o offset] [-l length] [-m minimum-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
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.
The offset, length, and minimum-free-extent arguments may be followed by binary (2^N) suf-
fixes 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 discard repeat-
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 set-
up, etc. These reductions would not be reflected in fstrim_range.len (the --length
Lukas Czerner <email@example.com>
Karel Zak <firstname.lastname@example.org>
The fstrim command is part of the util-linux package and is available from ftp://ftp.ker-
Nov 2010 FSTRIM(8)