FSTRIM(8)                   System Administration                  FSTRIM(8)

NAME         top

       fstrim - discard unused blocks on a mounted filesystem

SYNOPSIS         top

       fstrim [-a] [-o offset] [-l length] [-m minimum-free-extent] [-v]

DESCRIPTION         top

       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 more frequently or even using mount -o discard might
       affect lifetime of the poor quality SSD devices. The usual sufficient
       frequency is once a week for most desktop and server systems. Note
       that not all devices support queued trim, so each trim command incur
       a performance penalty to whatever else might be trying to use the
       disk at the time.

OPTIONS         top

       The offset, length, and minimum-free-extent 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.

       -h, --help
              Display help text 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 option).

RETURN CODES         top

       0      success

       1      failure

       32     all failed

       64     some filesystem discards have succeeded, some failed

       The command fstrim --all returns 0 (all success), 32 (all failed) or
       64 (some failed, some success).

AUTHOR         top

       Lukas Czerner <>
       Karel Zak <>

SEE ALSO         top


AVAILABILITY         top

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

COLOPHON         top

       This page is part of the util-linux (a random collection of Linux
       utilities) project.  Information about the project can be found at 
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util-linux                      November 2010                      FSTRIM(8)