FSTRIM(8) System Administration FSTRIM(8)
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 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.
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 de-
termined 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 filesys-
tem.
-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 mini-
mum, 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 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).
--quiet
Suppress trim operation (ioctl) 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)