1FSTRIM(8)                   System Manager's Manual                  FSTRIM(8)
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NAME

6       fstrim - discard unused blocks on a mounted filesystem
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SYNOPSIS

9       fstrim [-o offset] [-l length] [-m minimum-free-extent] [-v] mountpoint
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DESCRIPTION

13       fstrim  is  used  on a mounted filesystem to discard (or "trim") blocks
14       which are not in use by the filesystem.  This is useful for solid-state
15       drives (SSDs) and thinly-provisioned storage.
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17       By  default,  fstrim  will discard all unused blocks in the filesystem.
18       Options may be used to modify this behavior based on range or size,  as
19       explained below.
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21       The  mountpoint  argument  is  the  pathname of the directory where the
22       filesystem is mounted.
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OPTIONS

26       The offset, length, and minimum-free-extent arguments may  be  followed
27       by  binary  (2^N) suffixes KiB, MiB, GiB, TiB, PiB and EiB (the "iB" is
28       optional, e.g. "K" has the same meaning as  "KiB")  or  decimal  (10^N)
29       suffixes KB, MB, GB, PB and EB.
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31       -h, --help
32              Print help and exit.
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34       -o, --offset offset
35              Byte offset in filesystem from which to begin searching for free
36              blocks to discard.  Default  value  is  zero,  starting  at  the
37              beginning of the filesystem.
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39       -l, --length length
40              Number  of  bytes after starting point to search for free blocks
41              to discard.  If the specified value extends past the end of  the
42              filesystem,  fstrim  will  stop at the filesystem size boundary.
43              Default value extends to the end of the filesystem.
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45       -m, --minimum minimum-free-extent
46              Minimum contiguous free range to discard, in bytes. (This  value
47              is  internally  rounded up to a multiple of the filesystem block
48              size).  Free ranges smaller  than  this  will  be  ignored.   By
49              increasing  this  value, the fstrim operation will complete more
50              quickly  for  filesystems  with  badly   fragmented   freespace,
51              although  not  all  blocks  will be discarded.  Default value is
52              zero, discard every free block.
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54       -v, --verbose
55              Verbose execution. When specified fstrim will output the  number
56              of  bytes passed from the filesystem down the block stack to the
57              device for potential discard. This number is a  maximum  discard
58              amount  from  the  storage  device's perspective, because FITRIM
59              ioctl called repeated will keep sending  the  same  sectors  for
60              discard repeatedly.
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62              fstrim  will  report the same potential discard bytes each time,
63              but only sectors which had been written to between the  discards
64              would actually be discarded by the storage device.  Further, the
65              kernel block layer reserves the  right  to  adjust  the  discard
66              ranges  to fit raid stripe geometry, non-trim capable devices in
67              a LVM setup, etc.  These reductions would not  be  reflected  in
68              fstrim_range.len (the --length option).
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AUTHOR

72       Lukas Czerner <lczerner@redhat.com>
73       Karel Zak <kzak@redhat.com>
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SEE ALSO

76       mount(8)
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AVAILABILITY

79       The  fstrim  command is part of the util-linux-ng package and is avail‐
80       able from ftp://ftp.kernel.org/pub/linux/utils/util-linux-ng/.
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84                                   Nov 2010                          FSTRIM(8)