FSTRIM(8) System Administration FSTRIM(8)
fstrim - discard unused blocks on a mounted filesystem
fstrim [-a] [-o offset] [-l length] [-m minimum-size] [-v] mountpoint
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
The mountpoint argument is the pathname of the directory where the
filesystem is mounted.
Running fstrim frequently, or even using mount -o discard, might nega-
tively affect the lifetime of poor-quality SSD devices. For most desk-
top 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.
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.
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
-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 filesys-
-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.
Verbose execution. With this option fstrim will output the num-
ber of bytes passed from the filesystem down the block stack to
the device for potential discard. This number is a maximum dis-
card 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).
Display version information and exit.
Display help text and exit.
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).
Lukas Czerner <email@example.com>
Karel Zak <firstname.lastname@example.org>
The fstrim command is part of the util-linux package and is available
util-linux July 2014 FSTRIM(8)
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