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FSTRIM(8)                                                            FSTRIM(8)

       fstrim - discard unused blocks on a mounted filesystem

       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 behav-
       ior 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) 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.

       -h, --help
              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.

       -v, --verbose
              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

       Lukas Czerner <>
       Karel Zak <>


       The  fstrim  command  is  part  of  the  util-linux-ng   package   and   is   available   from   ftp://ftp.ker-

                                   Nov 2010                          FSTRIM(8)