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FSTRIM(8)                    System Administration                   FSTRIM(8)
NAME
       fstrim - discard unused blocks on a mounted filesystem
SYNOPSIS
       fstrim [-a] [-o offset] [-l length] [-m minimum-size] [-v] mountpoint
DESCRIPTION
       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  nega-
       tively affect the lifetime of poor-quality SSD devices.  For most desk-
       top and server systems a 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.
OPTIONS
       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.
       -a, --all
              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  filesys-
              tem.
       -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.  The default value is
              zero, discarding every free block.
       -v, --verbose
              Verbose execution.  With this option fstrim will output the num-
              ber of bytes passed from the filesystem down the block stack  to
              the device for potential discard.  This number is a maximum dis-
              card 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).
       -V, --version
              Display version information and exit.
       -h, --help
              Display help text and exit.
RETURN CODES
       0      success
       1      failure
       32     all failed
       64     some filesystem discards have succeeded, some failed
       The command fstrim --all returns 0 (all succeeded), 32 (all failed)  or
       64 (some failed, some succeeded).
AUTHOR
       Lukas Czerner <lczerner AT redhat.com>
       Karel Zak <kzak AT redhat.com>
SEE ALSO
       blkdiscard(8), mount(8)
AVAILABILITY
       The  fstrim  command is part of the util-linux package and is available
       from https://www.kernel.org/pub/linux/utils/util-linux/.
util-linux                         July 2014                         FSTRIM(8)