FSTRIM(8)		     System Administration		     FSTRIM(8)

NAME
       fstrim - discard unused blocks on a mounted filesystem

SYNOPSIS
       fstrim [-v] [-o offset] [-l length] [-m minimum-size] -A|-a|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 and is required when -A, -a, --fstab, or --all
       are unspecified.

       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, autofs and
	   read-only filesystems are silently ignored. Filesystems with
	   "X-fstrim.notrim" mount option are skipped.

       -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.

       -I, --listed-in list
	   Specifies a colon-separated list of files in fstab or kernel
	   mountinfo format. All missing or empty files are silently ignored.
	   The evaluation of the list stops after first non-empty file. For
	   example:

	   --listed-in /etc/fstab:/proc/self/mountinfo.

	   Filesystems with "X-fstrim.notrim" mount option in fstab are
	   skipped.

       -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.

       -t, --types list
	   Specifies allowed or forbidden filesystem types when used with
	   --all or --fstab.  The list is a comma-separated list of the
	   filesystem names. The list follows how mount -t evaluates type
	   patterns. Only specified filesystem types are allowed. All
	   specified types are forbidden if the list is prefixed by "no" or
	   each filesystem prefixed by "no" is forbidden. If the option is not
	   used, then all filesystems (except "autofs") are allowed.

       -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-unsupported
	   Suppress error messages if trim operation (ioctl) is unsupported.
	   This option is meant to be used in systemd service file or in
	   cron(8) 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. This option also cleans exit status when unsupported
	   filesystem specified on fstrim command line.

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

       -V, --version
	   Display version and exit.

EXIT STATUS
       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).

AUTHORS
       Lukas Czerner <lczerner@redhat.com>, Karel Zak <kzak@redhat.com>

SEE ALSO
       blkdiscard(8), mount(8)

REPORTING BUGS
       For bug reports, use the issue tracker
       <https://github.com/util-linux/util-linux/issues>.

AVAILABILITY
       The fstrim command is part of the util-linux package which can be
       downloaded from Linux Kernel Archive
       <https://www.kernel.org/pub/linux/utils/util-linux/>.

util-linux 2.41.2		  2025-09-22			     FSTRIM(8)