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  negatively  affect  the
       lifetime  of poor-quality SSD devices.  For most desktop and server systems the 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  suf‐
       fixes  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 dis‐
              card.  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 dis‐
              card.  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
              filesystem.

       -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.  Default value is zero, discard 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 repeat‐
              edly.

              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 set‐
              up, 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
       mount(8)

AVAILABILITY
       The fstrim command is part of the util-linux package and is available from  ftp://ftp.ker‐
       nel.org/pub/linux/utils/util-linux/.



util-linux                                  July 2014                                   FSTRIM(8)