Provided by: util-linux_2.20.1-5.1ubuntu20.9_amd64 bug


       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

       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)
       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

              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).


       Lukas Czerner <>
       Karel Zak <>




       The  fstrim  command  is  part  of  the  util-linux  package   and   is   available   from