FSTRIM(8)                   System Administration                  FSTRIM(8)

NAME         top

       fstrim - discard unused blocks on a mounted filesystem

SYNOPSIS         top

       fstrim [-Aa] [-o offset] [-l length] [-m minimum-size] [-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 frequently, or even using mount -o discard, might
       negatively affect the lifetime of poor-quality SSD devices.  For most
       desktop 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         top

       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, --fstab
              Trim all mounted filesystems mentioned in /etc/fstab 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.

       -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.

       -n, --dry-run
              This option does everything apart from actually call FITRIM

       -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

       -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
              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).

       -V, --version
              Display version information and exit.

       -h, --help
              Display help text and exit.

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 succeeded), 32 (all failed)
       or 64 (some failed, some succeeded).

AUTHOR         top

       Lukas Czerner <>
       Karel Zak <>

SEE ALSO         top

       blkdiscard(8), mount(8)

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 
       ⟨⟩.  If you have a
       bug report for this manual page, send it to  This page was obtained from the
       project's upstream Git repository
       ⟨git://⟩ on
       2018-10-29.  (At that time, the date of the most recent commit that
       was found in the repository was 2018-10-24.)  If you discover any
       rendering problems in this HTML version of the page, or you believe
       there is a better or more up-to-date source for the page, or you have
       corrections or improvements to the information in this COLOPHON
       (which is not part of the original manual page), send a mail to

util-linux                        July 2014                        FSTRIM(8)

Pages that refer to this page: blkdiscard(8)