NAME

       fstrim - discard unused blocks on a mounted filesystem

SYNOPSIS

       fstrim [-Aa] [-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 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, --fstab
              Trim all mounted  filesystems  mentioned  in  /etc/fstab  on  devices  that  support  the  discard
              operation.   The  root  filesystem  is determined from kernel command line if missing in the file.
              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, read-only devices and
              read-only filesystems 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, read-only devices and read-only filesystems
              are silently ignored.

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

       -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 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 and fstrim
              will  adjust  the  minimum  if  it's  smaller  than  the  device's  minimum,   and   report   that
              (fstrim_range.minlen)  back  to  userspace.   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).

       --quiet
              Suppress error messages.  This option is meant to be used in  systemd  service  file  or  in  cron
              scripts to hide warnings that are result of known problems, such as NTFS driver reporting Bad file
              descriptor when device is mounted read-only, or lack of file system support for ioctl FITRIM call.

       -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@redhat.com>
       Karel Zak <kzak@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                                          May 2019                                           FSTRIM(8)